diff --git a/toolchain/check/import_cpp.cpp b/toolchain/check/import_cpp.cpp
index 6894fa440905..b9e2c9da5f6c 100644
--- a/toolchain/check/import_cpp.cpp
+++ b/toolchain/check/import_cpp.cpp
@@ -8,7 +8,7 @@
 #include <optional>
 #include <string>
 
-#include "clang/Frontend/TextDiagnosticPrinter.h"
+#include "clang/Frontend/TextDiagnostic.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Tooling/Tooling.h"
 #include "common/raw_string_ostream.h"
@@ -44,6 +44,87 @@ static auto GenerateCppIncludesHeaderCode(
   return code;
 }
 
+namespace {
+
+// Used to convert Clang diagnostics to Carbon diagnostics.
+class CarbonClangDiagnosticConsumer : public clang::DiagnosticConsumer {
+ public:
+  // Creates an instance with the location that triggers calling Clang.
+  // `context` must not be null.
+  explicit CarbonClangDiagnosticConsumer(Context* context, SemIRLoc loc)
+      : context_(context), loc_(loc) {}
+
+  // Generates a Carbon warning for each Clang warning and a Carbon error for
+  // each Clang error or fatal.
+  auto HandleDiagnostic(clang::DiagnosticsEngine::Level diag_level,
+                        const clang::Diagnostic& info) -> void override {
+    DiagnosticConsumer::HandleDiagnostic(diag_level, info);
+
+    llvm::SmallString<256> message;
+    info.FormatDiagnostic(message);
+
+    RawStringOstream diagnostics_stream;
+    clang::TextDiagnostic text_diagnostic(
+        diagnostics_stream,
+        // TODO: Consider allowing setting `LangOptions` or use
+        // `ASTContext::getLangOptions()`.
+        clang::LangOptions(),
+        // TODO: Consider allowing setting `DiagnosticOptions` or use
+        // `ASTUnit::getDiagnostics().::getLangOptions().getDiagnosticOptions()`.
+        new clang::DiagnosticOptions());
+    text_diagnostic.emitDiagnostic(
+        clang::FullSourceLoc(info.getLocation(), info.getSourceManager()),
+        diag_level, message, info.getRanges(), info.getFixItHints());
+
+    std::string diagnostics_str = diagnostics_stream.TakeStr();
+
+    switch (diag_level) {
+      case clang::DiagnosticsEngine::Ignored:
+      case clang::DiagnosticsEngine::Note:
+      case clang::DiagnosticsEngine::Remark: {
+        context_->TODO(
+            loc_, llvm::formatv(
+                      "Unsupported: C++ diagnostic level for diagnostic\n{0}",
+                      diagnostics_str));
+        return;
+      }
+      case clang::DiagnosticsEngine::Warning:
+      case clang::DiagnosticsEngine::Error:
+      case clang::DiagnosticsEngine::Fatal: {
+        // TODO: Adjust diagnostics to drop the Carbon file here, and then
+        // remove the "C++:\n" prefix.
+        CARBON_DIAGNOSTIC(CppInteropParseWarning, Warning, "C++:\n{0}",
+                          std::string);
+        CARBON_DIAGNOSTIC(CppInteropParseError, Error, "C++:\n{0}",
+                          std::string);
+        // TODO: This should be part of the location, instead of added as a note
+        // here.
+        CARBON_DIAGNOSTIC(InCppImport, Note, "in `Cpp` import");
+
+        // TODO: Use a more specific location.
+        context_->emitter()
+            .Build(SemIR::LocId::None,
+                   diag_level == clang::DiagnosticsEngine::Warning
+                       ? CppInteropParseWarning
+                       : CppInteropParseError,
+                   diagnostics_str)
+            .Note(loc_, InCppImport)
+            .Emit();
+        return;
+      }
+    }
+  }
+
+ private:
+  // The type-checking context in which we're running Clang.
+  Context* context_;
+
+  // The location that triggered calling Clang.
+  SemIRLoc loc_;
+};
+
+}  // namespace
+
 // Returns an AST for the C++ imports and a bool that represents whether
 // compilation errors where encountered or the generated AST is null due to an
 // error.
@@ -59,10 +140,8 @@ static auto GenerateAst(Context& context, llvm::StringRef importing_file_path,
   std::string diagnostics_str;
   llvm::raw_string_ostream diagnostics_stream(diagnostics_str);
 
-  llvm::IntrusiveRefCntPtr<clang::DiagnosticOptions> diagnostic_options(
-      new clang::DiagnosticOptions());
-  clang::TextDiagnosticPrinter diagnostics_consumer(diagnostics_stream,
-                                                    diagnostic_options.get());
+  CarbonClangDiagnosticConsumer diagnostics_consumer(&context, loc);
+
   // TODO: Share compilation flags with ClangRunner.
   auto ast = clang::tooling::buildASTFromCodeWithArgs(
       GenerateCppIncludesHeaderCode(context, imports),
@@ -74,28 +153,7 @@ static auto GenerateAst(Context& context, llvm::StringRef importing_file_path,
   // Remove link to the diagnostics consumer before its deletion.
   ast->getDiagnostics().setClient(nullptr);
 
-  // TODO: Implement and use a DynamicRecursiveASTVisitor to traverse the AST.
-  int num_errors = diagnostics_consumer.getNumErrors();
-  int num_warnings = diagnostics_consumer.getNumWarnings();
-  int num_imports = imports.size();
-  if (num_errors > 0) {
-    // TODO: Remove the warnings part when there are no warnings.
-    CARBON_DIAGNOSTIC(
-        CppInteropParseError, Error,
-        "{0} error{0:s} and {1} warning{1:s} in {2} `Cpp` import{2:s}:\n{3}",
-        Diagnostics::IntAsSelect, Diagnostics::IntAsSelect,
-        Diagnostics::IntAsSelect, std::string);
-    context.emitter().Emit(loc, CppInteropParseError, num_errors, num_warnings,
-                           num_imports, diagnostics_str);
-  } else if (num_warnings > 0) {
-    CARBON_DIAGNOSTIC(CppInteropParseWarning, Warning,
-                      "{0} warning{0:s} in `Cpp` {1} import{1:s}:\n{2}",
-                      Diagnostics::IntAsSelect, Diagnostics::IntAsSelect,
-                      std::string);
-    context.emitter().Emit(loc, CppInteropParseWarning, num_warnings,
-                           num_imports, diagnostics_str);
-  }
-  return {std::move(ast), !ast || num_errors > 0};
+  return {std::move(ast), !ast || diagnostics_consumer.getNumErrors() > 0};
 }
 
 // Adds a namespace for the `Cpp` import and returns its `NameScopeId`.
diff --git a/toolchain/check/testdata/interop/cpp/no_prelude/bad_import.carbon b/toolchain/check/testdata/interop/cpp/no_prelude/bad_import.carbon
index 5d2210e80d50..237a50c7a7e6 100644
--- a/toolchain/check/testdata/interop/cpp/no_prelude/bad_import.carbon
+++ b/toolchain/check/testdata/interop/cpp/no_prelude/bad_import.carbon
@@ -29,14 +29,15 @@ library "[[@TEST_NAME]]";
 import Cpp library "";
 
 // --- fail_import_cpp_library_file_with_quotes.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_import_cpp_library_file_with_quotes.carbon:[[@LINE+8]]:1: error: 1 error and 0 warnings in 1 `Cpp` import:
+// CHECK:STDERR: fail_import_cpp_library_file_with_quotes.carbon: error: C++:
 // CHECK:STDERR: fail_import_cpp_library_file_with_quotes.carbon.generated.cpp_imports.h:1:10: fatal error: '\"foo.h\"' file not found
 // CHECK:STDERR:     1 | #include "\"foo.h\""
 // CHECK:STDERR:       |          ^~~~~~~~~~~
 // CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_cpp_library_file_with_quotes.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "\"foo.h\"";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
diff --git a/toolchain/check/testdata/interop/cpp/no_prelude/cpp_diagnostics.carbon b/toolchain/check/testdata/interop/cpp/no_prelude/cpp_diagnostics.carbon
index f0d0b47c2194..e86f0573173c 100644
--- a/toolchain/check/testdata/interop/cpp/no_prelude/cpp_diagnostics.carbon
+++ b/toolchain/check/testdata/interop/cpp/no_prelude/cpp_diagnostics.carbon
@@ -13,15 +13,16 @@
 #error "error1"
 
 // --- fail_import_cpp_file_with_one_error.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_import_cpp_file_with_one_error.carbon:[[@LINE+9]]:1: error: 1 error and 0 warnings in 1 `Cpp` import:
+// CHECK:STDERR: fail_import_cpp_file_with_one_error.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_cpp_file_with_one_error.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_error.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
 // CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_cpp_file_with_one_error.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "one_error.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -33,18 +34,26 @@ import Cpp library "one_error.h";
 #error "error2"
 
 // --- fail_import_cpp_file_with_multiple_errors.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors.carbon:[[@LINE+12]]:1: error: 2 errors and 0 warnings in 1 `Cpp` import:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors.carbon: error: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors.h:3:2: error: "error2"
 // CHECK:STDERR:     3 | #error "error2"
 // CHECK:STDERR:       |  ^
 // CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "multiple_errors.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -55,15 +64,16 @@ import Cpp library "multiple_errors.h";
 #warning "warning1"
 
 // --- import_cpp_file_with_one_warning.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: import_cpp_file_with_one_warning.carbon:[[@LINE+9]]:1: warning: 1 warning in `Cpp` 1 import:
+// CHECK:STDERR: import_cpp_file_with_one_warning.carbon: warning: C++:
 // CHECK:STDERR: In file included from import_cpp_file_with_one_warning.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_warning.h:2:2: warning: "warning1"
 // CHECK:STDERR:     2 | #warning "warning1"
 // CHECK:STDERR:       |  ^
 // CHECK:STDERR:  [CppInteropParseWarning]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: import_cpp_file_with_one_warning.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "one_warning.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -76,21 +86,36 @@ import Cpp library "one_warning.h";
 #warning "warning3"
 
 // --- import_cpp_file_with_multiple_warnings.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon:[[@LINE+15]]:1: warning: 3 warnings in `Cpp` 1 import:
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon: warning: C++:
 // CHECK:STDERR: In file included from import_cpp_file_with_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_warnings.h:2:2: warning: "warning1"
 // CHECK:STDERR:     2 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon:[[@LINE+24]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from import_cpp_file_with_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_warnings.h:3:2: warning: "warning2"
 // CHECK:STDERR:     3 | #warning "warning2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from import_cpp_file_with_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_warnings.h:4:2: warning: "warning3"
 // CHECK:STDERR:     4 | #warning "warning3"
 // CHECK:STDERR:       |  ^
 // CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: import_cpp_file_with_multiple_warnings.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "multiple_warnings.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -102,18 +127,26 @@ import Cpp library "multiple_warnings.h";
 #warning "warning1"
 
 // --- fail_import_cpp_file_with_one_error_and_one_warning.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_import_cpp_file_with_one_error_and_one_warning.carbon:[[@LINE+12]]:1: error: 1 error and 1 warning in 1 `Cpp` import:
+// CHECK:STDERR: fail_import_cpp_file_with_one_error_and_one_warning.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_cpp_file_with_one_error_and_one_warning.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_error_and_one_warning.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_cpp_file_with_one_error_and_one_warning.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "one_error_and_one_warning.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_one_error_and_one_warning.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_one_error_and_one_warning.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_error_and_one_warning.h:3:2: warning: "warning1"
 // CHECK:STDERR:     3 | #warning "warning1"
 // CHECK:STDERR:       |  ^
-// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_cpp_file_with_one_error_and_one_warning.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "one_error_and_one_warning.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -128,93 +161,227 @@ import Cpp library "one_error_and_one_warning.h";
 #warning "warning3"
 
 // --- fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+21]]:1: error: 2 errors and 3 warnings in 1 `Cpp` import:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+44]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon: error: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:3:2: error: "error2"
 // CHECK:STDERR:     3 | #error "error2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+34]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:4:2: warning: "warning1"
 // CHECK:STDERR:     4 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+24]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:5:2: warning: "warning2"
 // CHECK:STDERR:     5 | #warning "warning2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:6:2: warning: "warning3"
 // CHECK:STDERR:     6 | #warning "warning3"
 // CHECK:STDERR:       |  ^
-// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_cpp_file_with_multiple_errors_and_multiple_warnings.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
 import Cpp library "multiple_errors_and_multiple_warnings.h";
 
 // --- import_multiple_cpp_files_with_warnings.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp library "one_warning.h";
-// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon:[[@LINE+19]]:1: warning: 4 warnings in `Cpp` 2 imports:
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon: warning: C++:
 // CHECK:STDERR: In file included from import_multiple_cpp_files_with_warnings.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_warning.h:2:2: warning: "warning1"
 // CHECK:STDERR:     2 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "one_warning.h";
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon:[[@LINE+34]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon: warning: C++:
 // CHECK:STDERR: In file included from import_multiple_cpp_files_with_warnings.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_warnings.h:2:2: warning: "warning1"
 // CHECK:STDERR:     2 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon:[[@LINE+24]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from import_multiple_cpp_files_with_warnings.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_warnings.h:3:2: warning: "warning2"
 // CHECK:STDERR:     3 | #warning "warning2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon: warning: C++:
+// CHECK:STDERR: In file included from import_multiple_cpp_files_with_warnings.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_warnings.h:4:2: warning: "warning3"
 // CHECK:STDERR:     4 | #warning "warning3"
 // CHECK:STDERR:       |  ^
 // CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: import_multiple_cpp_files_with_warnings.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "multiple_warnings.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
 import Cpp library "multiple_warnings.h";
 
 // --- fail_import_multiple_cpp_files_with_warnings_and_errors.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp library "one_error_and_one_warning.h";
-// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+28]]:1: error: 3 errors and 4 warnings in 2 `Cpp` imports:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_error_and_one_warning.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "one_error_and_one_warning.h";
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+64]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:1:
 // CHECK:STDERR: ./one_error_and_one_warning.h:3:2: warning: "warning1"
 // CHECK:STDERR:     3 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+54]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: error: C++:
 // CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:2:2: error: "error1"
 // CHECK:STDERR:     2 | #error "error1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+44]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: error: C++:
+// CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:3:2: error: "error2"
 // CHECK:STDERR:     3 | #error "error2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+34]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:4:2: warning: "warning1"
 // CHECK:STDERR:     4 | #warning "warning1"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+24]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:5:2: warning: "warning2"
 // CHECK:STDERR:     5 | #warning "warning2"
 // CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+14]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon: warning: C++:
+// CHECK:STDERR: In file included from fail_import_multiple_cpp_files_with_warnings_and_errors.carbon.generated.cpp_imports.h:2:
 // CHECK:STDERR: ./multiple_errors_and_multiple_warnings.h:6:2: warning: "warning3"
 // CHECK:STDERR:     6 | #warning "warning3"
 // CHECK:STDERR:       |  ^
-// CHECK:STDERR:  [CppInteropParseError]
+// CHECK:STDERR:  [CppInteropParseWarning]
+// CHECK:STDERR: fail_import_multiple_cpp_files_with_warnings_and_errors.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "multiple_errors_and_multiple_warnings.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
 import Cpp library "multiple_errors_and_multiple_warnings.h";
 
+// --- indirect_error.h
+
+#include "one_error.h"
+
+// --- fail_import_indirect_error.carbon
+// CHECK:STDERR: fail_import_indirect_error.carbon: error: C++:
+// CHECK:STDERR: In file included from fail_import_indirect_error.carbon.generated.cpp_imports.h:1:
+// CHECK:STDERR: In file included from ./indirect_error.h:2:
+// CHECK:STDERR: ./one_error.h:2:2: error: "error1"
+// CHECK:STDERR:     2 | #error "error1"
+// CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_indirect_error.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "indirect_error.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+import Cpp library "indirect_error.h";
+
+// --- indirect_warning.h
+
+#include "one_warning.h"
+
+// --- import_indirect_warning.carbon
+// CHECK:STDERR: import_indirect_warning.carbon: warning: C++:
+// CHECK:STDERR: In file included from import_indirect_warning.carbon.generated.cpp_imports.h:1:
+// CHECK:STDERR: In file included from ./indirect_warning.h:2:
+// CHECK:STDERR: ./one_warning.h:2:2: warning: "warning1"
+// CHECK:STDERR:     2 | #warning "warning1"
+// CHECK:STDERR:       |  ^
+// CHECK:STDERR:  [CppInteropParseWarning]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: import_indirect_warning.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
+// CHECK:STDERR: import Cpp library "indirect_warning.h";
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+import Cpp library "indirect_warning.h";
+
 // CHECK:STDOUT: --- fail_import_cpp_file_with_one_error.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
@@ -358,3 +525,38 @@ import Cpp library "multiple_errors_and_multiple_warnings.h";
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_import_indirect_error.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:     has_error
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .Cpp = imports.%Cpp
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.import_cpp = import_cpp {
+// CHECK:STDOUT:     import Cpp "indirect_error.h"
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- import_indirect_warning.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .Cpp = imports.%Cpp
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.import_cpp = import_cpp {
+// CHECK:STDOUT:     import Cpp "indirect_warning.h"
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
diff --git a/toolchain/check/testdata/interop/cpp/no_prelude/file_not_found.carbon b/toolchain/check/testdata/interop/cpp/no_prelude/file_not_found.carbon
index 622b5e1083c2..40ea036cebbc 100644
--- a/toolchain/check/testdata/interop/cpp/no_prelude/file_not_found.carbon
+++ b/toolchain/check/testdata/interop/cpp/no_prelude/file_not_found.carbon
@@ -9,14 +9,15 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/no_prelude/file_not_found.carbon
 
 // --- fail_cpp_file_not_found.carbon
-
-library "[[@TEST_NAME]]";
-
-// CHECK:STDERR: fail_cpp_file_not_found.carbon:[[@LINE+8]]:1: error: 1 error and 0 warnings in 1 `Cpp` import:
+// CHECK:STDERR: fail_cpp_file_not_found.carbon: error: C++:
 // CHECK:STDERR: fail_cpp_file_not_found.carbon.generated.cpp_imports.h:1:10: fatal error: 'not_found.h' file not found
 // CHECK:STDERR:     1 | #include "not_found.h"
 // CHECK:STDERR:       |          ^~~~~~~~~~~~~
 // CHECK:STDERR:  [CppInteropParseError]
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_cpp_file_not_found.carbon:[[@LINE+4]]:1: note: in `Cpp` import [InCppImport]
 // CHECK:STDERR: import Cpp library "not_found.h";
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
diff --git a/toolchain/diagnostics/diagnostic_kind.def b/toolchain/diagnostics/diagnostic_kind.def
index 1168e3476fd5..794d13895572 100644
--- a/toolchain/diagnostics/diagnostic_kind.def
+++ b/toolchain/diagnostics/diagnostic_kind.def
@@ -157,6 +157,7 @@ CARBON_DIAGNOSTIC_KIND(RequirementEqualAfterNonDesignator)
 CARBON_DIAGNOSTIC_KIND(SemanticsTodo)
 
 // Location context.
+CARBON_DIAGNOSTIC_KIND(InCppImport)
 CARBON_DIAGNOSTIC_KIND(InImport)
 CARBON_DIAGNOSTIC_KIND(ResolvingSpecificHere)