Remove offsets from InstId formatting, trying to name more (#4645)

The offsets were originally added to deal with churn from builtins in
the raw semir. In textual semir, we mostly see instruction IDs for
imports, and builtins have also settled down more.

On imports, where possible, use the `EntityNameId` for an import instead
of printing an instruction. Next, show the source location if we have a
node. Only show the instruction if there's no location.

This also exposes `Parse::Tree` and `TokenizedBuffer`, so that we can
pass a `SemIR::File` without the component parts. In particular this
allows us to get the `TokenizedBuffer` for import IRs without
substantial structural modifications. We may want to make these optional
for serialized `SemIR` later, but the nodes/tokens contain source
location, which we'd need for debug information -- so it's not clear how
much we can really make them optional without substantial information
loss.

Reduce arguments to just `File` in a few spots, as a result of the
accompanying `TokenizedBuffer` and `Parse::Tree`. Also updates style to
pass around `const File*` where the reference is maintained, instead of
`const File&`.

I was considering keeping a direct reference to the tree and tokens on
`Context`, but initially my thought was it wouldn't make much
difference. I can re-add those if desired, just as direct caching of the
`File` fields.

toolchain/check/check.cpp

@@ -63,6 +63,11 @@ struct UnitInfo {
         err_tracker(*unit.consumer),
         emitter(*unit.node_converter, err_tracker) {}
 
+  auto parse_tree() -> const Parse::Tree& { return unit->sem_ir->parse_tree(); }
+  auto source() -> const SourceBuffer& {
+    return parse_tree().tokens().source();
+  }
+
   SemIR::CheckIRId check_ir_id;
   Unit* unit;
 
@@ -485,11 +490,10 @@ static auto CheckParseTree(UnitInfo& unit_info, int total_ir_count,
   // We can safely mark this as checked at the start.
   unit_info.is_checked = true;
 
-  SemIR::File& sem_ir = *unit_info.unit->sem_ir;
+  SemIR::File* sem_ir = unit_info.unit->sem_ir;
   Context::DiagnosticEmitter emitter(*unit_info.unit->sem_ir_converter,
                                      unit_info.err_tracker);
-  Context context(*unit_info.unit->tokens, emitter, *unit_info.unit->parse_tree,
-                  unit_info.unit->get_parse_tree_and_subtrees, sem_ir,
+  Context context(&emitter, unit_info.unit->get_parse_tree_and_subtrees, sem_ir,
                   vlog_stream);
   PrettyStackTraceFunction context_dumper(
       [&](llvm::raw_ostream& output) { context.PrintForStackDump(output); });
@@ -515,11 +519,11 @@ static auto CheckParseTree(UnitInfo& unit_info, int total_ir_count,
 
   context.VerifyOnFinish();
 
-  sem_ir.set_has_errors(unit_info.err_tracker.seen_error());
+  sem_ir->set_has_errors(unit_info.err_tracker.seen_error());
 
 #ifndef NDEBUG
-  if (auto verify = sem_ir.Verify(); !verify.ok()) {
-    CARBON_FATAL("{0}Built invalid semantics IR: {1}\n", sem_ir,
+  if (auto verify = sem_ir->Verify(); !verify.ok()) {
+    CARBON_FATAL("{0}Built invalid semantics IR: {1}\n", *sem_ir,
                  verify.error());
   }
 #endif
@@ -566,7 +570,7 @@ static auto TrackImport(Map<ImportKey, UnitInfo*>& api_map,
                         Map<ImportKey, Parse::NodeId>* explicit_import_map,
                         UnitInfo& unit_info, Parse::Tree::PackagingNames import)
     -> void {
-  const auto& packaging = unit_info.unit->parse_tree->packaging_decl();
+  const auto& packaging = unit_info.parse_tree().packaging_decl();
 
   IdentifierId file_package_id =
       packaging ? packaging->names.package_id : IdentifierId::Invalid;
@@ -712,7 +716,7 @@ static auto BuildApiMapAndDiagnosePackaging(
     llvm::MutableArrayRef<UnitInfo> unit_infos) -> Map<ImportKey, UnitInfo*> {
   Map<ImportKey, UnitInfo*> api_map;
   for (auto& unit_info : unit_infos) {
-    const auto& packaging = unit_info.unit->parse_tree->packaging_decl();
+    const auto& packaging = unit_info.parse_tree().packaging_decl();
     // An import key formed from the `package` or `library` declaration. Or, for
     // Main//default, a placeholder key.
     auto import_key = packaging ? GetImportKey(unit_info, IdentifierId::Invalid,
@@ -749,7 +753,7 @@ static auto BuildApiMapAndDiagnosePackaging(
       auto insert_result = api_map.Insert(import_key, &unit_info);
       if (!insert_result.is_inserted()) {
         llvm::StringRef prev_filename =
-            insert_result.value()->unit->tokens->source().filename();
+            insert_result.value()->source().filename();
         if (packaging) {
           CARBON_DIAGNOSTIC(DuplicateLibraryApi, Error,
                             "library's API previously provided by `{0}`",
@@ -770,8 +774,8 @@ static auto BuildApiMapAndDiagnosePackaging(
     // Validate file extensions. Note imports rely the packaging declaration,
     // not the extension. If the input is not a regular file, for example
     // because it is stdin, no filename checking is performed.
-    if (unit_info.unit->tokens->source().is_regular_file()) {
-      auto filename = unit_info.unit->tokens->source().filename();
+    if (unit_info.source().is_regular_file()) {
+      auto filename = unit_info.source().filename();
       static constexpr llvm::StringLiteral ApiExt = ".carbon";
       static constexpr llvm::StringLiteral ImplExt = ".impl.carbon";
       bool is_api_with_impl_ext = !is_impl && filename.ends_with(ImplExt);
@@ -814,7 +818,7 @@ auto CheckParseTrees(llvm::MutableArrayRef<Unit> units, bool prelude_import,
   llvm::SmallVector<UnitInfo*> ready_to_check;
   ready_to_check.reserve(units.size());
   for (auto& unit_info : unit_infos) {
-    const auto& packaging = unit_info.unit->parse_tree->packaging_decl();
+    const auto& packaging = unit_info.parse_tree().packaging_decl();
     if (packaging && packaging->is_impl) {
       // An `impl` has an implicit import of its `api`.
       auto implicit_names = packaging->names;
@@ -838,7 +842,7 @@ auto CheckParseTrees(llvm::MutableArrayRef<Unit> units, bool prelude_import,
                    .library_id = prelude_id});
     }
 
-    for (const auto& import : unit_info.unit->parse_tree->imports()) {
+    for (const auto& import : unit_info.parse_tree().imports()) {
       TrackImport(api_map, &explicit_import_map, unit_info, import);
     }