[clang] Fix range for forward-declared enums

This used to span just the `[[enum foo]] : bar;` in the absence of a
body. This patch expands the range to cover the base specifier, so that the
various consumers can detect the full range of the decl.

Differential Revision: https://reviews.llvm.org/D111259

clang/include/clang/AST/Decl.h

@@ -3701,6 +3701,10 @@ class EnumDecl : public TagDecl {
                           bool IsFixed);
   static EnumDecl *CreateDeserialized(ASTContext &C, unsigned ID);
 
+  /// Overrides to provide correct range when there's an enum-base specifier
+  /// with forward declarations.
+  SourceRange getSourceRange() const override LLVM_READONLY;
+
   /// When created, the EnumDecl corresponds to a
   /// forward-declared enum. This method is used to mark the
   /// declaration as being defined; its enumerators have already been

clang/lib/AST/Decl.cpp

@@ -4524,6 +4524,17 @@ unsigned EnumDecl::getODRHash() {
   return ODRHash;
 }
 
+SourceRange EnumDecl::getSourceRange() const {
+  auto Res = TagDecl::getSourceRange();
+  // Set end-point to enum-base, e.g. enum foo : ^bar
+  if (auto *TSI = getIntegerTypeSourceInfo()) {
+    // TagDecl doesn't know about the enum base.
+    if (!getBraceRange().getEnd().isValid())
+      Res.setEnd(TSI->getTypeLoc().getEndLoc());
+  }
+  return Res;
+}
+
 //===----------------------------------------------------------------------===//
 // RecordDecl Implementation
 //===----------------------------------------------------------------------===//

clang/unittests/AST/DeclTest.cpp

@@ -10,14 +10,17 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/AST/Decl.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Mangle.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Lex/Lexer.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/Testing/Support/Annotations.h"
 #include "gtest/gtest.h"
 
 using namespace clang::ast_matchers;
@@ -138,3 +141,19 @@ TEST(Decl, MangleDependentSizedArray) {
   ASSERT_TRUE(0 == MangleA.compare("_ZTSA_i"));
   ASSERT_TRUE(0 == MangleB.compare("_ZTSAT0__T_"));
 }
+
+TEST(Decl, EnumDeclRange) {
+  llvm::Annotations Code(R"(
+    typedef int Foo;
+    [[enum Bar : Foo]];)");
+  auto AST = tooling::buildASTFromCodeWithArgs(Code.code(), /*Args=*/{});
+  ASTContext &Ctx = AST->getASTContext();
+  const auto &SM = Ctx.getSourceManager();
+
+  const auto *Bar =
+      selectFirst<TagDecl>("Bar", match(enumDecl().bind("Bar"), Ctx));
+  auto BarRange =
+      Lexer::getAsCharRange(Bar->getSourceRange(), SM, Ctx.getLangOpts());
+  EXPECT_EQ(SM.getFileOffset(BarRange.getBegin()), Code.range().Begin);
+  EXPECT_EQ(SM.getFileOffset(BarRange.getEnd()), Code.range().End);
+}