[clangd] Define out-of-line qualify function name

Summary:
When moving function definitions to a different context, the function
name might need a different spelling, for example in the header it might be:

```
namespace a {
  void foo() {}
}
```

And we might want to move it into a context which doesn't have `namespace a` as
a parent, then we must re-spell the function name, i.e:
```
void a::foo() {}
```

This patch implements a version of this which ignores using namespace
declarations in the source file.

Reviewers: hokein

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D70656

clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp

@@ -136,7 +136,6 @@ getFunctionSourceAfterReplacements(const FunctionDecl *FD,
 // Contains function signature, body and template parameters if applicable.
 // No need to qualify parameters, as they are looked up in the context
 // containing the function/method.
-// FIXME: Qualify function name depending on the target context.
 llvm::Expected<std::string>
 getFunctionSourceCode(const FunctionDecl *FD, llvm::StringRef TargetNamespace) {
   auto &SM = FD->getASTContext().getSourceManager();
@@ -149,16 +148,17 @@ getFunctionSourceCode(const FunctionDecl *FD, llvm::StringRef TargetNamespace) {
   llvm::Error Errors = llvm::Error::success();
   tooling::Replacements QualifierInsertions;
 
-  // Finds the first unqualified name in function return type and qualifies it
-  // to be valid in TargetContext.
+  // Finds the first unqualified name in function return type and name, then
+  // qualifies those to be valid in TargetContext.
   findExplicitReferences(FD, [&](ReferenceLoc Ref) {
     // It is enough to qualify the first qualifier, so skip references with a
     // qualifier. Also we can't do much if there are no targets or name is
     // inside a macro body.
     if (Ref.Qualifier || Ref.Targets.empty() || Ref.NameLoc.isMacroID())
       return;
-    // Qualify return type
-    if (Ref.NameLoc != FD->getReturnTypeSourceRange().getBegin())
+    // Only qualify return type and function name.
+    if (Ref.NameLoc != FD->getReturnTypeSourceRange().getBegin() &&
+        Ref.NameLoc != FD->getLocation())
       return;
 
     for (const NamedDecl *ND : Ref.Targets) {
@@ -293,9 +293,7 @@ public:
     auto FuncDef =
         getFunctionSourceCode(Source, InsertionPoint->EnclosingNamespace);
     if (!FuncDef)
-      return llvm::createStringError(
-          llvm::inconvertibleErrorCode(),
-          "Couldn't get full source for function definition.");
+      return FuncDef.takeError();
 
     SourceManagerForFile SMFF(*CCFile, Contents);
     const tooling::Replacement InsertFunctionDef(

clang-tools-extra/clangd/unittests/TweakTests.cpp

@@ -2004,7 +2004,7 @@ TEST_F(DefineOutlineTest, QualifyReturnValue) {
             Bar foo() ;
           };
         })cpp",
-       "a::Foo::Bar foo() { return {}; }\n"},
+       "a::Foo::Bar a::Foo::foo() { return {}; }\n"},
       {R"cpp(
         class Foo;
         Foo fo^o() { return; })cpp",
@@ -2022,6 +2022,58 @@ TEST_F(DefineOutlineTest, QualifyReturnValue) {
   }
 }
 
+TEST_F(DefineOutlineTest, QualifyFunctionName) {
+  FileName = "Test.hpp";
+  struct {
+    llvm::StringRef TestHeader;
+    llvm::StringRef TestSource;
+    llvm::StringRef ExpectedHeader;
+    llvm::StringRef ExpectedSource;
+  } Cases[] = {
+      {
+          R"cpp(
+            namespace a {
+              namespace b {
+                class Foo {
+                  void fo^o() {}
+                };
+              }
+            })cpp",
+          "",
+          R"cpp(
+            namespace a {
+              namespace b {
+                class Foo {
+                  void foo() ;
+                };
+              }
+            })cpp",
+          "void a::b::Foo::foo() {}\n",
+      },
+      {
+          "namespace a { namespace b { void f^oo() {} } }",
+          "namespace a{}",
+          "namespace a { namespace b { void foo() ; } }",
+          "namespace a{void b::foo() {} }",
+      },
+      {
+          "namespace a { namespace b { void f^oo() {} } }",
+          "using namespace a;",
+          "namespace a { namespace b { void foo() ; } }",
+          // FIXME: Take using namespace directives in the source file into
+          // account. This can be spelled as b::foo instead.
+          "using namespace a;void a::b::foo() {} ",
+      },
+  };
+  llvm::StringMap<std::string> EditedFiles;
+  for (auto &Case : Cases) {
+    ExtraFiles["Test.cpp"] = Case.TestSource;
+    EXPECT_EQ(apply(Case.TestHeader, &EditedFiles), Case.ExpectedHeader);
+    EXPECT_THAT(EditedFiles, testing::ElementsAre(FileWithContents(
+                                 testPath("Test.cpp"), Case.ExpectedSource)))
+        << Case.TestHeader;
+  }
+}
 } // namespace
 } // namespace clangd
 } // namespace clang