diff --git a/toolchain/check/check.cpp b/toolchain/check/check.cpp
index ce5577cd9707..f1835605fe97 100644
--- a/toolchain/check/check.cpp
+++ b/toolchain/check/check.cpp
@@ -36,10 +36,11 @@ class SemIRDiagnosticConverter : public DiagnosticConverter<SemIRLocation> {
       const SemIR::File* sem_ir)
       : node_converters_(node_converters), sem_ir_(sem_ir) {}
 
-  auto ConvertLocation(SemIRLocation loc) const -> DiagnosticLocation override {
+  auto ConvertLocation(SemIRLocation loc, ContextFnT context_fn) const
+      -> DiagnosticLocation override {
     // Parse nodes always refer to the current IR.
     if (!loc.is_inst_id) {
-      return ConvertLocationInFile(sem_ir_, loc.node_location);
+      return ConvertLocationInFile(sem_ir_, loc.node_location, context_fn);
     }
 
     const auto* cursor_ir = sem_ir_;
@@ -48,14 +49,19 @@ class SemIRDiagnosticConverter : public DiagnosticConverter<SemIRLocation> {
       // If the parse node is valid, use it for the location.
       if (auto node_id = cursor_ir->insts().GetNodeId(cursor_inst_id);
           node_id.is_valid()) {
-        return ConvertLocationInFile(cursor_ir, node_id);
+        return ConvertLocationInFile(cursor_ir, node_id, context_fn);
       }
 
       // If the parse node was invalid, recurse through import references when
       // possible.
       if (auto import_ref = cursor_ir->insts().TryGetAs<SemIR::AnyImportRef>(
               cursor_inst_id)) {
-        cursor_ir = cursor_ir->import_irs().Get(import_ref->ir_id);
+        const auto& import_ir = cursor_ir->import_irs().Get(import_ref->ir_id);
+        auto context_loc =
+            ConvertLocationInFile(cursor_ir, import_ir.node_id, context_fn);
+        CARBON_DIAGNOSTIC(InImport, Note, "In import.");
+        context_fn(context_loc, InImport);
+        cursor_ir = import_ir.sem_ir;
         cursor_inst_id = import_ref->inst_id;
         continue;
       }
@@ -71,7 +77,8 @@ class SemIRDiagnosticConverter : public DiagnosticConverter<SemIRLocation> {
       }
 
       // Invalid parse node but not an import; just nothing to point at.
-      return ConvertLocationInFile(cursor_ir, Parse::NodeId::Invalid);
+      return ConvertLocationInFile(cursor_ir, Parse::NodeId::Invalid,
+                                   context_fn);
     }
   }
 
@@ -91,11 +98,12 @@ class SemIRDiagnosticConverter : public DiagnosticConverter<SemIRLocation> {
 
  private:
   auto ConvertLocationInFile(const SemIR::File* sem_ir,
-                             Parse::NodeLocation node_location) const
+                             Parse::NodeLocation node_location,
+                             ContextFnT context_fn) const
       -> DiagnosticLocation {
     auto it = node_converters_->find(sem_ir);
     CARBON_CHECK(it != node_converters_->end());
-    return it->second->ConvertLocation(node_location);
+    return it->second->ConvertLocation(node_location, context_fn);
   }
 
   const llvm::DenseMap<const SemIR::File*, Parse::NodeLocationConverter*>*
@@ -191,7 +199,7 @@ static auto InitPackageScopeAndImports(Context& context, UnitInfo& unit_info)
     for (const auto& import : self_import->second.imports) {
       const auto& import_sem_ir = **import.unit_info->unit->sem_ir;
       ImportLibraryFromCurrentPackage(context, namespace_type_id,
-                                      import_sem_ir);
+                                      import.names.node_id, import_sem_ir);
       error_in_import |= import_sem_ir.name_scopes()
                              .Get(SemIR::NameScopeId::Package)
                              .has_error;
@@ -216,13 +224,14 @@ static auto InitPackageScopeAndImports(Context& context, UnitInfo& unit_info)
       continue;
     }
 
-    llvm::SmallVector<const SemIR::File*> sem_irs;
+    llvm::SmallVector<SemIR::ImportIR> import_irs;
     for (auto import : package_imports.imports) {
-      sem_irs.push_back(&**import.unit_info->unit->sem_ir);
+      import_irs.push_back({.node_id = import.names.node_id,
+                            .sem_ir = &**import.unit_info->unit->sem_ir});
     }
     ImportLibrariesFromOtherPackage(context, namespace_type_id,
                                     package_imports.node_id, package_id,
-                                    sem_irs, package_imports.has_load_error);
+                                    import_irs, package_imports.has_load_error);
   }
 
   CARBON_CHECK(context.import_irs().size() == num_irs)
diff --git a/toolchain/check/context.cpp b/toolchain/check/context.cpp
index 8a055777d7c7..bdb3a61c2542 100644
--- a/toolchain/check/context.cpp
+++ b/toolchain/check/context.cpp
@@ -137,7 +137,7 @@ auto Context::ReplaceInstBeforeConstantUse(
 auto Context::AddImportRef(SemIR::ImportIRId ir_id, SemIR::InstId inst_id)
     -> SemIR::InstId {
   auto import_ref_id =
-      AddPlaceholderInstInNoBlock(SemIR::ImportRefUnused{ir_id, inst_id});
+      AddPlaceholderInstInNoBlock({SemIR::ImportRefUnused{ir_id, inst_id}});
 
   // We can't insert this instruction into whatever block we happen to be in,
   // because this function is typically called by name lookup in the middle of
@@ -303,7 +303,8 @@ static auto LookupInImportIRScopes(Context& context, SemIRLocation loc,
     // Determine the NameId in the import IR.
     SemIR::NameId import_name_id = name_id;
     if (identifier_id.is_valid()) {
-      auto import_identifier_id = import_ir->identifiers().Lookup(identifier);
+      auto import_identifier_id =
+          import_ir.sem_ir->identifiers().Lookup(identifier);
       if (!import_identifier_id.is_valid()) {
         // Name doesn't exist in the import IR.
         continue;
@@ -312,7 +313,8 @@ static auto LookupInImportIRScopes(Context& context, SemIRLocation loc,
     }
 
     // Look up the name in the import scope.
-    const auto& import_scope = import_ir->name_scopes().Get(import_scope_id);
+    const auto& import_scope =
+        import_ir.sem_ir->name_scopes().Get(import_scope_id);
     auto it = import_scope.names.find(import_name_id);
     if (it == import_scope.names.end()) {
       // Name doesn't exist in the import scope.
@@ -742,7 +744,7 @@ class TypeCompleter {
   auto BuildImportRefUsedValueRepr(SemIR::TypeId type_id,
                                    SemIR::ImportRefUsed import_ref) const
       -> SemIR::ValueRepr {
-    const auto& import_ir = context_.import_irs().Get(import_ref.ir_id);
+    const auto& import_ir = context_.import_irs().Get(import_ref.ir_id).sem_ir;
     auto import_inst = import_ir->insts().Get(import_ref.inst_id);
     CARBON_CHECK(import_inst.kind() != SemIR::InstKind::ImportRefUsed)
         << "If ImportRefUsed can point at another, this would be recursive.";
diff --git a/toolchain/check/import.cpp b/toolchain/check/import.cpp
index 1425e640436e..68ae266d76df 100644
--- a/toolchain/check/import.cpp
+++ b/toolchain/check/import.cpp
@@ -130,12 +130,11 @@ static auto CacheCopiedNamespace(
 // name conflicts, but that won't change the result because namespaces supersede
 // other names in conflicts.
 static auto CopySingleNameScopeFromImportIR(
-    Context& context,
+    Context& context, SemIR::TypeId namespace_type_id,
     llvm::DenseMap<SemIR::NameScopeId, SemIR::NameScopeId>& copied_namespaces,
     SemIR::ImportIRId ir_id, SemIR::InstId import_inst_id,
     SemIR::NameScopeId import_scope_id, SemIR::NameScopeId enclosing_scope_id,
-    SemIR::NameId name_id, SemIR::TypeId namespace_type_id)
-    -> SemIR::NameScopeId {
+    SemIR::NameId name_id) -> SemIR::NameScopeId {
   // Produce the namespace for the entry.
   auto make_import_id = [&]() {
     return context.AddInst(SemIR::ImportRefUsed{.type_id = namespace_type_id,
@@ -199,8 +198,8 @@ static auto CopyEnclosingNameScopesFromImportIR(
     auto name_id =
         CopyNameFromImportIR(context, import_sem_ir, import_scope.name_id);
     scope_cursor = CopySingleNameScopeFromImportIR(
-        context, copied_namespaces, ir_id, import_scope.inst_id,
-        import_scope_id, scope_cursor, name_id, namespace_type_id);
+        context, namespace_type_id, copied_namespaces, ir_id,
+        import_scope.inst_id, import_scope_id, scope_cursor, name_id);
   }
 
   return scope_cursor;
@@ -208,8 +207,10 @@ static auto CopyEnclosingNameScopesFromImportIR(
 
 auto ImportLibraryFromCurrentPackage(Context& context,
                                      SemIR::TypeId namespace_type_id,
+                                     Parse::ImportDirectiveId node_id,
                                      const SemIR::File& import_sem_ir) -> void {
-  auto ir_id = context.import_irs().Add(&import_sem_ir);
+  auto ir_id =
+      context.import_irs().Add({.node_id = node_id, .sem_ir = &import_sem_ir});
   context.import_ir_constant_values()[ir_id.index].Set(
       SemIR::InstId::PackageNamespace,
       context.constant_values().Get(SemIR::InstId::PackageNamespace));
@@ -236,9 +237,8 @@ auto ImportLibraryFromCurrentPackage(Context& context,
       // Namespaces are always imported because they're essential for
       // qualifiers, and the type is simple.
       CopySingleNameScopeFromImportIR(
-          context, copied_namespaces, ir_id, import_inst_id,
-          import_namespace_inst->name_scope_id, enclosing_scope_id, name_id,
-          namespace_type_id);
+          context, namespace_type_id, copied_namespaces, ir_id, import_inst_id,
+          import_namespace_inst->name_scope_id, enclosing_scope_id, name_id);
     } else {
       // Leave a placeholder that the inst comes from the other IR.
       auto target_id = context.AddImportRef(ir_id, import_inst_id);
@@ -260,9 +260,9 @@ auto ImportLibrariesFromOtherPackage(Context& context,
                                      SemIR::TypeId namespace_type_id,
                                      Parse::ImportDirectiveId node_id,
                                      IdentifierId package_id,
-                                     llvm::ArrayRef<const SemIR::File*> sem_irs,
+                                     llvm::ArrayRef<SemIR::ImportIR> import_irs,
                                      bool has_load_error) -> void {
-  CARBON_CHECK(has_load_error || !sem_irs.empty())
+  CARBON_CHECK(has_load_error || !import_irs.empty())
       << "There should be either a load error or at least one IR.";
 
   auto name_id = SemIR::NameId::ForIdentifier(package_id);
@@ -273,8 +273,8 @@ auto ImportLibrariesFromOtherPackage(Context& context,
 
   auto& scope = context.name_scopes().Get(namespace_scope_id);
   scope.is_closed_import = !is_duplicate;
-  for (const auto* sem_ir : sem_irs) {
-    auto ir_id = context.import_irs().Add(sem_ir);
+  for (auto import_ir : import_irs) {
+    auto ir_id = context.import_irs().Add(import_ir);
     scope.import_ir_scopes.push_back({ir_id, SemIR::NameScopeId::Package});
     context.import_ir_constant_values()[ir_id.index].Set(
         SemIR::InstId::PackageNamespace, namespace_const_id);
diff --git a/toolchain/check/import.h b/toolchain/check/import.h
index 5f4849d92650..e680a3f31545 100644
--- a/toolchain/check/import.h
+++ b/toolchain/check/import.h
@@ -6,6 +6,7 @@
 #define CARBON_TOOLCHAIN_CHECK_IMPORT_H_
 
 #include "toolchain/check/context.h"
+#include "toolchain/parse/node_ids.h"
 #include "toolchain/sem_ir/file.h"
 
 namespace Carbon::Check {
@@ -15,6 +16,7 @@ namespace Carbon::Check {
 // though they are several layers deep.
 auto ImportLibraryFromCurrentPackage(Context& context,
                                      SemIR::TypeId namespace_type_id,
+                                     Parse::ImportDirectiveId node_id,
                                      const SemIR::File& import_sem_ir) -> void;
 
 // Adds another package's imports to name lookup, with all libraries together.
@@ -22,13 +24,13 @@ auto ImportLibraryFromCurrentPackage(Context& context,
 // will resolve, and will provide a name scope that can be used for further
 // qualified name lookups.
 //
-// sem_irs will all be non-null, and may be empty. has_load_error is used to
-// indicate if any library in the package failed to import correctly.
+// import_irs may be empty. has_load_error is used to indicate if any library in
+// the package failed to import correctly.
 auto ImportLibrariesFromOtherPackage(Context& context,
                                      SemIR::TypeId namespace_type_id,
                                      Parse::ImportDirectiveId node_id,
                                      IdentifierId package_id,
-                                     llvm::ArrayRef<const SemIR::File*> sem_irs,
+                                     llvm::ArrayRef<SemIR::ImportIR> import_irs,
                                      bool has_load_error) -> void;
 
 }  // namespace Carbon::Check
diff --git a/toolchain/check/import_ref.cpp b/toolchain/check/import_ref.cpp
index e77c4757f179..492bdff7f526 100644
--- a/toolchain/check/import_ref.cpp
+++ b/toolchain/check/import_ref.cpp
@@ -57,7 +57,7 @@ class ImportRefResolver {
   explicit ImportRefResolver(Context& context, SemIR::ImportIRId import_ir_id)
       : context_(context),
         import_ir_id_(import_ir_id),
-        import_ir_(*context_.import_irs().Get(import_ir_id)),
+        import_ir_(*context_.import_irs().Get(import_ir_id).sem_ir),
         import_ir_constant_values_(
             context_.import_ir_constant_values()[import_ir_id.index]) {}
 
@@ -912,7 +912,8 @@ auto TryResolveImportRefUnused(Context& context, SemIR::InstId inst_id)
     return;
   }
 
-  const SemIR::File& import_ir = *context.import_irs().Get(import_ref->ir_id);
+  const SemIR::File& import_ir =
+      *context.import_irs().Get(import_ref->ir_id).sem_ir;
   auto import_inst = import_ir.insts().Get(import_ref->inst_id);
 
   ImportRefResolver resolver(context, import_ref->ir_id);
diff --git a/toolchain/check/testdata/class/cross_package_import.carbon b/toolchain/check/testdata/class/cross_package_import.carbon
index b8844eaaf66a..b185436797e1 100644
--- a/toolchain/check/testdata/class/cross_package_import.carbon
+++ b/toolchain/check/testdata/class/cross_package_import.carbon
@@ -45,17 +45,11 @@ library "extern" api;
 
 import Other library "extern";
 
-// CHECK:STDERR: fail_extern.carbon:[[@LINE+11]]:8: ERROR: Variable has incomplete type `C`.
+// CHECK:STDERR: fail_extern.carbon:[[@LINE+5]]:8: ERROR: Variable has incomplete type `C`.
 // CHECK:STDERR: var c: Other.C = {};
 // CHECK:STDERR:        ^~~~~~~
 // CHECK:STDERR: fail_extern.carbon: Class was forward declared here.
 // CHECK:STDERR:
-// CHECK:STDERR: other_extern.carbon:5:1: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: class C;
-// CHECK:STDERR: ^~~~~~~~
-// CHECK:STDERR: other_define.carbon:4:1: Name is previously declared here.
-// CHECK:STDERR: class C {}
-// CHECK:STDERR: ^~~~~~~~~
 var c: Other.C = {};
 
 // --- fail_merge_define_extern.carbon
@@ -63,18 +57,24 @@ var c: Other.C = {};
 library "fail_merge_define_extern" api;
 
 import Other library "define";
-import Other library "extern";
-
-// CHECK:STDERR: fail_merge_define_extern.carbon:[[@LINE+10]]:8: In name lookup for `C`.
-// CHECK:STDERR: var c: Other.C = {};
-// CHECK:STDERR:        ^~~~~~~
-// CHECK:STDERR:
-// CHECK:STDERR: other_conflict.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: fn C() {}
+// CHECK:STDERR: fail_merge_define_extern.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import Other library "extern";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_extern.carbon:5:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: class C;
 // CHECK:STDERR: ^~~~~~~~
+// CHECK:STDERR: fail_merge_define_extern.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import Other library "define";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: other_define.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: class C {}
 // CHECK:STDERR: ^~~~~~~~~
+import Other library "extern";
+
+// CHECK:STDERR: fail_merge_define_extern.carbon:[[@LINE+4]]:8: In name lookup for `C`.
+// CHECK:STDERR: var c: Other.C = {};
+// CHECK:STDERR:        ^~~~~~~
+// CHECK:STDERR:
 var c: Other.C = {};
 
 // --- fail_conflict.carbon
@@ -82,6 +82,18 @@ var c: Other.C = {};
 library "conflict" api;
 
 import Other library "define";
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import Other library "conflict";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_conflict.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fn C() {}
+// CHECK:STDERR: ^~~~~~~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import Other library "define";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_define.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: class C {}
+// CHECK:STDERR: ^~~~~~~~~
 import Other library "conflict";
 
 // CHECK:STDERR: fail_conflict.carbon:[[@LINE+3]]:8: In name lookup for `C`.
@@ -201,7 +213,7 @@ var c: Other.C = {};
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @__global_init() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %.loc17: {} = struct_literal ()
+// CHECK:STDOUT:   %.loc11: {} = struct_literal ()
 // CHECK:STDOUT:   assign file.%c.var, <error>
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
@@ -243,10 +255,10 @@ var c: Other.C = {};
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @__global_init() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %.loc17_19.1: {} = struct_literal ()
-// CHECK:STDOUT:   %.loc17_19.2: init C = class_init (), file.%c.var [template = constants.%.4]
-// CHECK:STDOUT:   %.loc17_19.3: init C = converted %.loc17_19.1, %.loc17_19.2 [template = constants.%.4]
-// CHECK:STDOUT:   assign file.%c.var, %.loc17_19.3
+// CHECK:STDOUT:   %.loc23_19.1: {} = struct_literal ()
+// CHECK:STDOUT:   %.loc23_19.2: init C = class_init (), file.%c.var [template = constants.%.4]
+// CHECK:STDOUT:   %.loc23_19.3: init C = converted %.loc23_19.1, %.loc23_19.2 [template = constants.%.4]
+// CHECK:STDOUT:   assign file.%c.var, %.loc23_19.3
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -285,10 +297,10 @@ var c: Other.C = {};
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @__global_init() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %.loc10_19.1: {} = struct_literal ()
-// CHECK:STDOUT:   %.loc10_19.2: init C = class_init (), file.%c.var [template = constants.%.4]
-// CHECK:STDOUT:   %.loc10_19.3: init C = converted %.loc10_19.1, %.loc10_19.2 [template = constants.%.4]
-// CHECK:STDOUT:   assign file.%c.var, %.loc10_19.3
+// CHECK:STDOUT:   %.loc22_19.1: {} = struct_literal ()
+// CHECK:STDOUT:   %.loc22_19.2: init C = class_init (), file.%c.var [template = constants.%.4]
+// CHECK:STDOUT:   %.loc22_19.3: init C = converted %.loc22_19.1, %.loc22_19.2 [template = constants.%.4]
+// CHECK:STDOUT:   assign file.%c.var, %.loc22_19.3
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/class/fail_import_misuses.carbon b/toolchain/check/testdata/class/fail_import_misuses.carbon
index 62dee713bced..2edb61eec4eb 100644
--- a/toolchain/check/testdata/class/fail_import_misuses.carbon
+++ b/toolchain/check/testdata/class/fail_import_misuses.carbon
@@ -19,9 +19,12 @@ library "b" api;
 
 import library "a";
 
-// CHECK:STDERR: fail_b.carbon:[[@LINE+7]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_b.carbon:[[@LINE+10]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: class Empty {
 // CHECK:STDERR: ^~~~~~~~~~~~~
+// CHECK:STDERR: fail_b.carbon:[[@LINE-5]]:1: In import.
+// CHECK:STDERR: import library "a";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: a.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: class Empty {
 // CHECK:STDERR: ^~~~~~~~~~~~~
diff --git a/toolchain/check/testdata/class/fail_todo_import_forward_decl.carbon b/toolchain/check/testdata/class/fail_todo_import_forward_decl.carbon
index 005a5863393c..f33152fdcc7f 100644
--- a/toolchain/check/testdata/class/fail_todo_import_forward_decl.carbon
+++ b/toolchain/check/testdata/class/fail_todo_import_forward_decl.carbon
@@ -17,9 +17,12 @@ library "b" api;
 import library "a";
 
 // TODO: This should probably have a valid form.
-// CHECK:STDERR: fail_b.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_b.carbon:[[@LINE+9]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: class ForwardDecl {
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_b.carbon:[[@LINE-6]]:1: In import.
+// CHECK:STDERR: import library "a";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: a.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: class ForwardDecl;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
diff --git a/toolchain/check/testdata/function/definition/fail_todo_import_forward_decl.carbon b/toolchain/check/testdata/function/definition/fail_todo_import_forward_decl.carbon
index 1d89ea3f3a03..06008179cc44 100644
--- a/toolchain/check/testdata/function/definition/fail_todo_import_forward_decl.carbon
+++ b/toolchain/check/testdata/function/definition/fail_todo_import_forward_decl.carbon
@@ -18,9 +18,12 @@ import library "a";
 
 // TODO: This should be an error until we can be clear whether `a` or `b` should
 // own the definition, as there might be a separate definition in `a`'s impl.
-// CHECK:STDERR: fail_b.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_b.carbon:[[@LINE+9]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: fn Foo() {}
 // CHECK:STDERR: ^~~~~~~~~~
+// CHECK:STDERR: fail_b.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import library "a";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: a.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: fn Foo();
 // CHECK:STDERR: ^~~~~~~~~
@@ -44,7 +47,7 @@ fn Foo() {}
 // CHECK:STDOUT:     .Foo = %import_ref
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %import_ref: <function> = import_ref ir1, inst+1, used [template = imports.%Foo]
-// CHECK:STDOUT:   %.loc14: <function> = fn_decl @.1 [template] {}
+// CHECK:STDOUT:   %.loc17: <function> = fn_decl @.1 [template] {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @Foo();
diff --git a/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_first.carbon b/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_first.carbon
index 9b91dd6ebbdf..86a481fa02ef 100644
--- a/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_first.carbon
+++ b/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_first.carbon
@@ -16,9 +16,12 @@ package Example api;
 
 import library "namespace";
 
-// CHECK:STDERR: fail_conflict.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+9]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: fn NS();
 // CHECK:STDERR: ^~~~~~~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-5]]:1: In import.
+// CHECK:STDERR: import library "namespace";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: namespace.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: namespace NS;
 // CHECK:STDERR: ^~~~~~~~~~~~~
@@ -45,7 +48,7 @@ fn NS.Foo();
 // CHECK:STDOUT:   %NS: <namespace> = namespace %import_ref, [template] {
 // CHECK:STDOUT:     .Foo = %Foo
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %.loc12: <function> = fn_decl @.1 [template] {}
+// CHECK:STDOUT:   %.loc15: <function> = fn_decl @.1 [template] {}
 // CHECK:STDOUT:   %Foo: <function> = fn_decl @Foo [template] {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_second.carbon b/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_second.carbon
index 879b9e1d0dec..69a34bc18c04 100644
--- a/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_second.carbon
+++ b/toolchain/check/testdata/namespace/fail_conflict_imported_namespace_second.carbon
@@ -16,9 +16,12 @@ package Example api;
 
 import library "fn";
 
-// CHECK:STDERR: fail_conflict.carbon:[[@LINE+7]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+10]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: namespace NS;
 // CHECK:STDERR: ^~~~~~~~~~~~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-5]]:1: In import.
+// CHECK:STDERR: import library "fn";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: fn.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: fn NS();
 // CHECK:STDERR: ^~~~~~~~
@@ -51,8 +54,8 @@ fn NS.Foo();
 // CHECK:STDOUT:     .NS = %import_ref
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %import_ref: <function> = import_ref ir1, inst+1, used [template = imports.%NS]
-// CHECK:STDOUT:   %.loc13: <namespace> = namespace [template] {}
-// CHECK:STDOUT:   %.loc21: <function> = fn_decl @.1 [template] {}
+// CHECK:STDOUT:   %.loc16: <namespace> = namespace [template] {}
+// CHECK:STDOUT:   %.loc24: <function> = fn_decl @.1 [template] {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @NS();
diff --git a/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_first.carbon b/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_first.carbon
index d520e5be005d..9913595042dc 100644
--- a/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_first.carbon
+++ b/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_first.carbon
@@ -15,12 +15,6 @@ fn NS.Foo() {}
 
 package Example library "fn" api;
 
-// CHECK:STDERR: fn.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: fn NS() {}
-// CHECK:STDERR: ^~~~~~~~~
-// CHECK:STDERR: namespace.carbon:4:1: Name is previously declared here.
-// CHECK:STDERR: namespace NS;
-// CHECK:STDERR: ^~~~~~~~~~~~~
 fn NS() {}
 
 // --- fail_conflict.carbon
@@ -28,6 +22,18 @@ fn NS() {}
 package Example library "namespace_then_fn" api;
 
 import library "namespace";
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import library "fn";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: fn.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fn NS() {}
+// CHECK:STDERR: ^~~~~~~~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import library "namespace";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: namespace.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: namespace NS;
+// CHECK:STDERR: ^~~~~~~~~~~~~
 import library "fn";
 
 fn NS.Bar() {}
diff --git a/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_second.carbon b/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_second.carbon
index c43c641f1cef..0b013c38dcdb 100644
--- a/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_second.carbon
+++ b/toolchain/check/testdata/namespace/fail_conflict_in_imports_namespace_second.carbon
@@ -14,12 +14,6 @@ fn NS() {}
 
 package Example library "namespace" api;
 
-// CHECK:STDERR: namespace.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: namespace NS;
-// CHECK:STDERR: ^~~~~~~~~~~~~
-// CHECK:STDERR: fn.carbon:4:1: Name is previously declared here.
-// CHECK:STDERR: fn NS() {}
-// CHECK:STDERR: ^~~~~~~~~
 namespace NS;
 fn NS.Foo() {}
 
@@ -28,6 +22,18 @@ fn NS.Foo() {}
 package Example library "fn_then_namespace" api;
 
 import library "fn";
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import library "namespace";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: namespace.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: namespace NS;
+// CHECK:STDERR: ^~~~~~~~~~~~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import library "fn";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: fn.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: fn NS() {}
+// CHECK:STDERR: ^~~~~~~~~
 import library "namespace";
 
 fn NS.Bar() {}
diff --git a/toolchain/check/testdata/packages/cross_package_import.carbon b/toolchain/check/testdata/packages/cross_package_import.carbon
index f36bda608968..1d9e28be561a 100644
--- a/toolchain/check/testdata/packages/cross_package_import.carbon
+++ b/toolchain/check/testdata/packages/cross_package_import.carbon
@@ -19,12 +19,6 @@ fn F() {}
 package Other library "fn_extern" api;
 
 // TODO: Mark extern
-// CHECK:STDERR: other_fn_extern.carbon:[[@LINE+6]]:1: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: fn F();
-// CHECK:STDERR: ^~~~~~~
-// CHECK:STDERR: other_fn.carbon:4:1: Name is previously declared here.
-// CHECK:STDERR: fn F() {}
-// CHECK:STDERR: ^~~~~~~~
 fn F();
 
 // --- other_fn_conflict.carbon
@@ -66,19 +60,25 @@ fn Run() {
 library "use_other_extern" api;
 
 import Other library "fn";
+// CHECK:STDERR: fail_main_use_other_extern.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import Other library "fn_extern";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_fn_extern.carbon:5:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fn F();
+// CHECK:STDERR: ^~~~~~~
+// CHECK:STDERR: fail_main_use_other_extern.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import Other library "fn";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_fn.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: fn F() {}
+// CHECK:STDERR: ^~~~~~~~
 import Other library "fn_extern";
 
 fn Run() {
-  // CHECK:STDERR: fail_main_use_other_extern.carbon:[[@LINE+10]]:3: In name lookup for `F`.
+  // CHECK:STDERR: fail_main_use_other_extern.carbon:[[@LINE+4]]:3: In name lookup for `F`.
   // CHECK:STDERR:   Other.F();
   // CHECK:STDERR:   ^~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: other_fn_conflict.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
-  // CHECK:STDERR: fn F(x: i32) {}
-  // CHECK:STDERR: ^~~~~~~~~~~~~~
-  // CHECK:STDERR: other_fn.carbon:4:1: Name is previously declared here.
-  // CHECK:STDERR: fn F() {}
-  // CHECK:STDERR: ^~~~~~~~
   Other.F();
 }
 
@@ -94,6 +94,18 @@ import Other library "fn_conflict";
 library "use_other_ambiguous" api;
 
 import Other library "fn";
+// CHECK:STDERR: fail_main_use_other_ambiguous.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import Other library "fn_conflict";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_fn_conflict.carbon:4:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fn F(x: i32) {}
+// CHECK:STDERR: ^~~~~~~~~~~~~~
+// CHECK:STDERR: fail_main_use_other_ambiguous.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import Other library "fn";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: other_fn.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: fn F() {}
+// CHECK:STDERR: ^~~~~~~~
 import Other library "fn_conflict";
 
 fn Run() {
@@ -109,18 +121,24 @@ fn Run() {
 library "namespace_conflict" api;
 
 import library "other_ns";
-// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE+7]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE+10]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: import Other library "fn";
 // CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE-4]]:1: In import.
+// CHECK:STDERR: import library "other_ns";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: main_other_ns.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: namespace Other;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~
 // CHECK:STDERR:
 import Other library "fn";
 
-// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE+7]]:1: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE+10]]:1: ERROR: Duplicate name being declared in the same scope.
 // CHECK:STDERR: fn Other.F() {}
 // CHECK:STDERR: ^~~~~~~~~~~~~~
+// CHECK:STDERR: fail_main_namespace_conflict.carbon:[[@LINE-5]]:1: In import.
+// CHECK:STDERR: import Other library "fn";
+// CHECK:STDERR: ^~~~~~
 // CHECK:STDERR: other_fn.carbon:4:1: Name is previously declared here.
 // CHECK:STDERR: fn F() {}
 // CHECK:STDERR: ^~~~~~~~
@@ -277,7 +295,7 @@ fn Other.G() {}
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   %Other.ref: <namespace> = name_ref Other, file.%Other [template = file.%Other]
 // CHECK:STDOUT:   %F.ref: <function> = name_ref F, file.%import_ref.1 [template = imports.%F.1]
-// CHECK:STDOUT:   %.loc18: init () = call %F.ref()
+// CHECK:STDOUT:   %.loc24: init () = call %F.ref()
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -315,7 +333,7 @@ fn Other.G() {}
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   %Other.ref: <namespace> = name_ref Other, file.%Other [template = file.%Other]
 // CHECK:STDOUT:   %F.ref: <function> = name_ref F, file.%import_ref.1 [template = imports.%F.1]
-// CHECK:STDOUT:   %.loc12: init () = call %F.ref()
+// CHECK:STDOUT:   %.loc24: init () = call %F.ref()
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -332,7 +350,7 @@ fn Other.G() {}
 // CHECK:STDOUT:   %import_ref.1: <namespace> = import_ref ir1, inst+1, used
 // CHECK:STDOUT:   %Other: <namespace> = namespace %import_ref.1, [template] {}
 // CHECK:STDOUT:   %import_ref.2: <function> = import_ref ir2, inst+1, used [template = imports.%F]
-// CHECK:STDOUT:   %.loc21: <function> = fn_decl @.1 [template] {}
+// CHECK:STDOUT:   %.loc27: <function> = fn_decl @.1 [template] {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F();
diff --git a/toolchain/check/testdata/packages/fail_conflict_no_namespaces.carbon b/toolchain/check/testdata/packages/fail_conflict_no_namespaces.carbon
index feb2b8aec7b2..ad3927d9f082 100644
--- a/toolchain/check/testdata/packages/fail_conflict_no_namespaces.carbon
+++ b/toolchain/check/testdata/packages/fail_conflict_no_namespaces.carbon
@@ -14,12 +14,6 @@ fn Foo();
 
 package Example library "var" api;
 
-// CHECK:STDERR: var.carbon:[[@LINE+6]]:5: ERROR: Duplicate name being declared in the same scope.
-// CHECK:STDERR: var Foo: i32;
-// CHECK:STDERR:     ^~~
-// CHECK:STDERR: fn.carbon:4:1: Name is previously declared here.
-// CHECK:STDERR: fn Foo();
-// CHECK:STDERR: ^~~~~~~~~
 var Foo: i32;
 
 // --- fail_conflict.carbon
@@ -27,6 +21,18 @@ var Foo: i32;
 package Example library "conflict" api;
 
 import library "fn";
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE+12]]:1: In import.
+// CHECK:STDERR: import library "var";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: var.carbon:4:5: ERROR: Duplicate name being declared in the same scope.
+// CHECK:STDERR: var Foo: i32;
+// CHECK:STDERR:     ^~~
+// CHECK:STDERR: fail_conflict.carbon:[[@LINE-7]]:1: In import.
+// CHECK:STDERR: import library "fn";
+// CHECK:STDERR: ^~~~~~
+// CHECK:STDERR: fn.carbon:4:1: Name is previously declared here.
+// CHECK:STDERR: fn Foo();
+// CHECK:STDERR: ^~~~~~~~~
 import library "var";
 
 // CHECK:STDOUT: --- fn.carbon
diff --git a/toolchain/diagnostics/diagnostic_converter.h b/toolchain/diagnostics/diagnostic_converter.h
index ebc28e033e3f..e043ce56f9d3 100644
--- a/toolchain/diagnostics/diagnostic_converter.h
+++ b/toolchain/diagnostics/diagnostic_converter.h
@@ -15,9 +15,18 @@ namespace Carbon {
 template <typename LocationT>
 class DiagnosticConverter {
  public:
+  // Callback type used to report context messages from ConvertLocation.
+  // Note that the first parameter type is DiagnosticLocation rather than
+  // LocationT, because ConvertLocation must not recurse.
+  using ContextFnT = llvm::function_ref<void(
+      DiagnosticLocation, const Internal::DiagnosticBase<>&)>;
+
   virtual ~DiagnosticConverter() = default;
 
-  virtual auto ConvertLocation(LocationT loc) const -> DiagnosticLocation = 0;
+  // Converts a LocationT to a DiagnosticLocation. ConvertLocation may invoke
+  // context_fn to provide context messages.
+  virtual auto ConvertLocation(LocationT loc, ContextFnT context_fn) const
+      -> DiagnosticLocation = 0;
 
   // Converts arg types as needed. Not all uses require conversion, so the
   // default returns the argument unchanged.
diff --git a/toolchain/diagnostics/diagnostic_emitter.h b/toolchain/diagnostics/diagnostic_emitter.h
index c27ff91ad024..6ca20c3761b1 100644
--- a/toolchain/diagnostics/diagnostic_emitter.h
+++ b/toolchain/diagnostics/diagnostic_emitter.h
@@ -65,8 +65,7 @@ class DiagnosticEmitter {
               Internal::NoTypeDeduction<Args>... args) -> DiagnosticBuilder& {
       CARBON_CHECK(diagnostic_base.Level == DiagnosticLevel::Note)
           << static_cast<int>(diagnostic_base.Level);
-      AddMessage(emitter_, location, diagnostic_base,
-                 {emitter_->MakeAny<Args>(args)...});
+      AddMessage(location, diagnostic_base, {emitter_->MakeAny<Args>(args)...});
       return *this;
     }
 
@@ -89,18 +88,39 @@ class DiagnosticEmitter {
         const Internal::DiagnosticBase<Args...>& diagnostic_base,
         llvm::SmallVector<llvm::Any> args)
         : emitter_(emitter), diagnostic_({.level = diagnostic_base.Level}) {
-      AddMessage(emitter, location, diagnostic_base, std::move(args));
+      AddMessage(location, diagnostic_base, std::move(args));
       CARBON_CHECK(diagnostic_base.Level != DiagnosticLevel::Note);
     }
 
+    // Adds a message to the diagnostic, handling conversion of the location and
+    // arguments.
     template <typename... Args>
-    auto AddMessage(DiagnosticEmitter<LocationT>* emitter, LocationT location,
+    auto AddMessage(LocationT location,
                     const Internal::DiagnosticBase<Args...>& diagnostic_base,
                     llvm::SmallVector<llvm::Any> args) -> void {
+      AddMessageWithDiagnosticLocation(
+          emitter_->converter_->ConvertLocation(
+              location,
+              [&](DiagnosticLocation location,
+                  const Internal::DiagnosticBase<>& diagnostic_base) {
+                AddMessageWithDiagnosticLocation(location, diagnostic_base,
+                                                 args);
+              }),
+          diagnostic_base, args);
+    }
+
+    // Adds a message to the diagnostic, handling conversion of the arguments. A
+    // DiagnosticLocation must be provided instead of a LocationT in order to
+    // avoid potential recursion.
+    template <typename... Args>
+    auto AddMessageWithDiagnosticLocation(
+        DiagnosticLocation location,
+        const Internal::DiagnosticBase<Args...>& diagnostic_base,
+        llvm::SmallVector<llvm::Any> args) {
       diagnostic_.messages.emplace_back(DiagnosticMessage{
           .kind = diagnostic_base.Kind,
           .level = diagnostic_base.Level,
-          .location = emitter->converter_->ConvertLocation(location),
+          .location = location,
           .format = diagnostic_base.Format,
           .format_args = std::move(args),
           .format_fn = [](const DiagnosticMessage& message) -> std::string {
diff --git a/toolchain/diagnostics/diagnostic_emitter_test.cpp b/toolchain/diagnostics/diagnostic_emitter_test.cpp
index c689c62e157e..b68fdb0970fe 100644
--- a/toolchain/diagnostics/diagnostic_emitter_test.cpp
+++ b/toolchain/diagnostics/diagnostic_emitter_test.cpp
@@ -18,7 +18,8 @@ using ::Carbon::Testing::IsSingleDiagnostic;
 using testing::ElementsAre;
 
 struct FakeDiagnosticConverter : DiagnosticConverter<int> {
-  auto ConvertLocation(int n) const -> DiagnosticLocation override {
+  auto ConvertLocation(int n, ContextFnT /*context_fn*/) const
+      -> DiagnosticLocation override {
     return {.line_number = 1, .column_number = n};
   }
 };
diff --git a/toolchain/diagnostics/diagnostic_kind.def b/toolchain/diagnostics/diagnostic_kind.def
index 00823cb05966..728a77d7f8d4 100644
--- a/toolchain/diagnostics/diagnostic_kind.def
+++ b/toolchain/diagnostics/diagnostic_kind.def
@@ -127,6 +127,9 @@ CARBON_DIAGNOSTIC_KIND(ExpectedAliasInitializer)
 
 CARBON_DIAGNOSTIC_KIND(SemanticsTodo)
 
+// Location context.
+CARBON_DIAGNOSTIC_KIND(InImport)
+
 // Package/import checking diagnostics.
 CARBON_DIAGNOSTIC_KIND(IncorrectExtension)
 CARBON_DIAGNOSTIC_KIND(IncorrectExtensionImplNote)
diff --git a/toolchain/diagnostics/null_diagnostics.h b/toolchain/diagnostics/null_diagnostics.h
index c36dcd7cf3bc..5e9c6f8e3f45 100644
--- a/toolchain/diagnostics/null_diagnostics.h
+++ b/toolchain/diagnostics/null_diagnostics.h
@@ -11,8 +11,10 @@ namespace Carbon {
 
 template <typename LocationT>
 inline auto NullDiagnosticConverter() -> DiagnosticConverter<LocationT>& {
-  struct Converter : DiagnosticConverter<LocationT> {
-    auto ConvertLocation(LocationT /*loc*/) const
+  struct Converter : public DiagnosticConverter<LocationT> {
+    auto ConvertLocation(
+        LocationT /*loc*/,
+        DiagnosticConverter<LocationT>::ContextFnT /*context_fn*/) const
         -> DiagnosticLocation override {
       return {};
     }
diff --git a/toolchain/diagnostics/sorting_diagnostic_consumer_test.cpp b/toolchain/diagnostics/sorting_diagnostic_consumer_test.cpp
index ef237e3d4ba0..ba3337145c04 100644
--- a/toolchain/diagnostics/sorting_diagnostic_consumer_test.cpp
+++ b/toolchain/diagnostics/sorting_diagnostic_consumer_test.cpp
@@ -20,7 +20,7 @@ using ::testing::InSequence;
 CARBON_DIAGNOSTIC(TestDiagnostic, Error, "{0}", llvm::StringLiteral);
 
 struct FakeDiagnosticConverter : DiagnosticConverter<DiagnosticLocation> {
-  auto ConvertLocation(DiagnosticLocation loc) const
+  auto ConvertLocation(DiagnosticLocation loc, ContextFnT /*context_fn*/) const
       -> DiagnosticLocation override {
     return loc;
   }
diff --git a/toolchain/lex/test_helpers.h b/toolchain/lex/test_helpers.h
index 7d5d6418e3e2..2510a90ad7bd 100644
--- a/toolchain/lex/test_helpers.h
+++ b/toolchain/lex/test_helpers.h
@@ -24,7 +24,8 @@ class SingleTokenDiagnosticConverter : public DiagnosticConverter<const char*> {
   explicit SingleTokenDiagnosticConverter(llvm::StringRef token)
       : token_(token) {}
 
-  auto ConvertLocation(const char* pos) const -> DiagnosticLocation override {
+  auto ConvertLocation(const char* pos, ContextFnT /*context_fn*/) const
+      -> DiagnosticLocation override {
     CARBON_CHECK(StringRefContainsPointer(token_, pos))
         << "invalid diagnostic location";
     llvm::StringRef prefix = token_.take_front(pos - token_.begin());
diff --git a/toolchain/lex/tokenized_buffer.cpp b/toolchain/lex/tokenized_buffer.cpp
index 2af12fb3478d..65984170d463 100644
--- a/toolchain/lex/tokenized_buffer.cpp
+++ b/toolchain/lex/tokenized_buffer.cpp
@@ -346,7 +346,7 @@ auto TokenIterator::Print(llvm::raw_ostream& output) const -> void {
 }
 
 auto TokenizedBuffer::SourceBufferDiagnosticConverter::ConvertLocation(
-    const char* loc) const -> DiagnosticLocation {
+    const char* loc, ContextFnT /*context_fn*/) const -> DiagnosticLocation {
   CARBON_CHECK(StringRefContainsPointer(buffer_->source_->text(), loc))
       << "location not within buffer";
   int64_t offset = loc - buffer_->source_->text().begin();
@@ -390,7 +390,8 @@ auto TokenizedBuffer::SourceBufferDiagnosticConverter::ConvertLocation(
           .column_number = column_number + 1};
 }
 
-auto TokenDiagnosticConverter::ConvertLocation(TokenIndex token) const
+auto TokenDiagnosticConverter::ConvertLocation(TokenIndex token,
+                                               ContextFnT context_fn) const
     -> DiagnosticLocation {
   // Map the token location into a position within the source buffer.
   const auto& token_info = buffer_->GetTokenInfo(token);
@@ -403,7 +404,7 @@ auto TokenDiagnosticConverter::ConvertLocation(TokenIndex token) const
   // is a recovery token that doesn't correspond to the original source?
   DiagnosticLocation loc =
       TokenizedBuffer::SourceBufferDiagnosticConverter(buffer_).ConvertLocation(
-          token_start);
+          token_start, context_fn);
   loc.length = buffer_->GetTokenText(token).size();
   return loc;
 }
diff --git a/toolchain/lex/tokenized_buffer.h b/toolchain/lex/tokenized_buffer.h
index b5bafde87cd0..af30bc8d39f5 100644
--- a/toolchain/lex/tokenized_buffer.h
+++ b/toolchain/lex/tokenized_buffer.h
@@ -119,7 +119,8 @@ class TokenDiagnosticConverter : public DiagnosticConverter<TokenIndex> {
       : buffer_(buffer) {}
 
   // Map the given token into a diagnostic location.
-  auto ConvertLocation(TokenIndex token) const -> DiagnosticLocation override;
+  auto ConvertLocation(TokenIndex token, ContextFnT context_fn) const
+      -> DiagnosticLocation override;
 
  private:
   const TokenizedBuffer* buffer_;
@@ -255,7 +256,8 @@ class TokenizedBuffer : public Printable<TokenizedBuffer> {
 
     // Map the given position within the source buffer into a diagnostic
     // location.
-    auto ConvertLocation(const char* loc) const -> DiagnosticLocation override;
+    auto ConvertLocation(const char* loc, ContextFnT context_fn) const
+        -> DiagnosticLocation override;
 
    private:
     const TokenizedBuffer* buffer_;
diff --git a/toolchain/parse/tree_node_diagnostic_converter.h b/toolchain/parse/tree_node_diagnostic_converter.h
index a6b13019981e..546f3a4a487a 100644
--- a/toolchain/parse/tree_node_diagnostic_converter.h
+++ b/toolchain/parse/tree_node_diagnostic_converter.h
@@ -44,7 +44,7 @@ class NodeLocationConverter : public DiagnosticConverter<NodeLocation> {
         parse_tree_(parse_tree) {}
 
   // Map the given token into a diagnostic location.
-  auto ConvertLocation(NodeLocation node_location) const
+  auto ConvertLocation(NodeLocation node_location, ContextFnT context_fn) const
       -> DiagnosticLocation override {
     // Support the invalid token as a way to emit only the filename, when there
     // is no line association.
@@ -54,7 +54,7 @@ class NodeLocationConverter : public DiagnosticConverter<NodeLocation> {
 
     if (node_location.token_only()) {
       return token_converter_.ConvertLocation(
-          parse_tree_->node_token(node_location.node_id()));
+          parse_tree_->node_token(node_location.node_id()), context_fn);
     }
 
     // Construct a location that encompasses all tokens that descend from this
@@ -74,11 +74,12 @@ class NodeLocationConverter : public DiagnosticConverter<NodeLocation> {
       }
     }
     DiagnosticLocation start_loc =
-        token_converter_.ConvertLocation(start_token);
+        token_converter_.ConvertLocation(start_token, context_fn);
     if (start_token == end_token) {
       return start_loc;
     }
-    DiagnosticLocation end_loc = token_converter_.ConvertLocation(end_token);
+    DiagnosticLocation end_loc =
+        token_converter_.ConvertLocation(end_token, context_fn);
     // For multiline locations we simply return the rest of the line for now
     // since true multiline locations are not yet supported.
     if (start_loc.line_number != end_loc.line_number) {
diff --git a/toolchain/sem_ir/file.cpp b/toolchain/sem_ir/file.cpp
index 1b1ac0d78b37..549337aec3f5 100644
--- a/toolchain/sem_ir/file.cpp
+++ b/toolchain/sem_ir/file.cpp
@@ -9,6 +9,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "toolchain/base/value_store.h"
 #include "toolchain/base/yaml.h"
+#include "toolchain/parse/node_ids.h"
 #include "toolchain/sem_ir/builtin_kind.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/inst.h"
@@ -69,7 +70,8 @@ File::File(SharedValueStores& value_stores, std::string filename,
       inst_blocks_(allocator_),
       constants_(*this, allocator_) {
   CARBON_CHECK(builtins != nullptr);
-  auto builtins_id = import_irs_.Add(builtins);
+  auto builtins_id =
+      import_irs_.Add({.node_id = Parse::NodeId::Invalid, .sem_ir = builtins});
   CARBON_CHECK(builtins_id == ImportIRId::Builtins)
       << "Builtins must be the first IR";
 
@@ -105,8 +107,8 @@ File::File(SharedValueStores& value_stores, std::string filename,
         for (auto [i, inst] : llvm::enumerate(builtins->insts_.array_ref())) {
           // We can reuse the type_id from the builtin IR's inst because they're
           // special-cased values.
-          insts_.AddInNoBlock({ImportRefUsed{
-              inst.type_id(), ImportIRId::Builtins, SemIR::InstId(i)}});
+          insts_.AddInNoBlock(ImportRefUsed{
+              inst.type_id(), ImportIRId::Builtins, SemIR::InstId(i)});
         }
       }) {}
 
@@ -374,8 +376,9 @@ static auto StringifyTypeExprImpl(const SemIR::File& outer_sem_ir,
       }
       case ImportRefUsed::Kind: {
         auto import_ref = inst.As<ImportRefUsed>();
-        steps.push_back({.sem_ir = *sem_ir.import_irs().Get(import_ref.ir_id),
-                         .inst_id = import_ref.inst_id});
+        steps.push_back(
+            {.sem_ir = *sem_ir.import_irs().Get(import_ref.ir_id).sem_ir,
+             .inst_id = import_ref.inst_id});
         break;
       }
       case InterfaceType::Kind: {
@@ -556,7 +559,7 @@ auto GetExprCategory(const File& file, InstId inst_id) -> ExprCategory {
 
       case ImportRefUsed::Kind: {
         auto import_ref = inst.As<ImportRefUsed>();
-        ir = ir->import_irs().Get(import_ref.ir_id);
+        ir = ir->import_irs().Get(import_ref.ir_id).sem_ir;
         inst_id = import_ref.inst_id;
         continue;
       }
diff --git a/toolchain/sem_ir/file.h b/toolchain/sem_ir/file.h
index 21da089b019e..038d2d5abd2f 100644
--- a/toolchain/sem_ir/file.h
+++ b/toolchain/sem_ir/file.h
@@ -38,6 +38,17 @@ struct BindNameInfo : public Printable<BindNameInfo> {
   NameScopeId enclosing_scope_id;
 };
 
+class File;
+
+struct ImportIR : public Printable<ImportIR> {
+  auto Print(llvm::raw_ostream& out) const -> void { out << node_id; }
+
+  // The node ID for the import.
+  Parse::ImportDirectiveId node_id;
+  // The imported IR.
+  const File* sem_ir;
+};
+
 // Provides semantic analysis on a Parse::Tree.
 class File : public Printable<File> {
  public:
diff --git a/toolchain/sem_ir/ids.h b/toolchain/sem_ir/ids.h
index 1079e5e8157e..9bb6577165bc 100644
--- a/toolchain/sem_ir/ids.h
+++ b/toolchain/sem_ir/ids.h
@@ -20,6 +20,7 @@ class Inst;
 struct BindNameInfo;
 struct Class;
 struct Function;
+struct ImportIR;
 struct Interface;
 struct Impl;
 struct NameScope;
@@ -248,7 +249,7 @@ constexpr ImplId ImplId::Invalid = ImplId(InvalidIndex);
 
 // The ID of an imported IR.
 struct ImportIRId : public IdBase, public Printable<ImportIRId> {
-  using ValueType = const File*;
+  using ValueType = ImportIR;
 
   static const ImportIRId Builtins;
   using IdBase::IdBase;
diff --git a/toolchain/source/source_buffer.cpp b/toolchain/source/source_buffer.cpp
index c2887663c697..09248e2be823 100644
--- a/toolchain/source/source_buffer.cpp
+++ b/toolchain/source/source_buffer.cpp
@@ -12,7 +12,8 @@ namespace Carbon {
 
 namespace {
 struct FilenameConverter : DiagnosticConverter<llvm::StringRef> {
-  auto ConvertLocation(llvm::StringRef filename) const
+  auto ConvertLocation(llvm::StringRef filename,
+                       ContextFnT /*context_fn*/) const
       -> DiagnosticLocation override {
     return {.filename = filename};
   }