[clangd] Preserve qualified names in "override pure virtual methods" tweak (#163726)

Prevents the tweak from splitting **qualified names** (e.g.,
`foo::Type`) by incorrectly inserting a space around the scope
resolution (`::`).

**Before:**

```cpp
// input:
virtual foo::Type::func() = 0 
// output:
foo :: Type :: func()
```

**After:**

```cpp
// input:
virtual foo::Type::func() = 0 
// output:
foo::Type::func()
```

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

diff --git a/clang-tools-extra/clangd/refactor/tweaks/OverridePureVirtuals.cpp b/clang-tools-extra/clangd/refactor/tweaks/OverridePureVirtuals.cpp
index 16febec..b557066 100644
--- a/clang-tools-extra/clangd/refactor/tweaks/OverridePureVirtuals.cpp
+++ b/clang-tools-extra/clangd/refactor/tweaks/OverridePureVirtuals.cpp
@@ -79,7 +79,7 @@
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclCXX.h"
-#include "clang/AST/Type.h"
+#include "clang/AST/TypeBase.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/SourceLocation.h"
@@ -116,7 +116,8 @@
 
     DeclString += Tk.text();
     if (Tk.Kind != tok::l_paren && Next.Kind != tok::comma &&
-        Next.Kind != tok::r_paren && Next.Kind != tok::l_paren)
+        Next.Kind != tok::r_paren && Next.Kind != tok::l_paren &&
+        Tk.Kind != tok::coloncolon && Next.Kind != tok::coloncolon)
       DeclString += ' ';
   }
   // Trim the last whitespace.

clang-tools-extra/clangd/unittests/tweaks/OverridePureVirtualsTests.cpp

diff --git a/clang-tools-extra/clangd/unittests/tweaks/OverridePureVirtualsTests.cpp b/clang-tools-extra/clangd/unittests/tweaks/OverridePureVirtualsTests.cpp
index b7dcbee..72095ab 100644
--- a/clang-tools-extra/clangd/unittests/tweaks/OverridePureVirtualsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/tweaks/OverridePureVirtualsTests.cpp
@@ -715,6 +715,45 @@
   EXPECT_EQ(Expected, Applied) << "Applied result:\n" << Applied;
 }
 
+TEST_F(OverridePureVirtualsTests, QualifiedNames) {
+  constexpr auto Before = R"cpp(
+namespace foo { struct S{}; namespace bar { struct S2{}; } }
+
+class B {
+public:
+  virtual foo::S foo(int var = 0) = 0;
+  virtual foo::bar::S2 bar(int var = 0) = 0;
+};
+
+class ^D : public B {};
+)cpp";
+
+  constexpr auto Expected = R"cpp(
+namespace foo { struct S{}; namespace bar { struct S2{}; } }
+
+class B {
+public:
+  virtual foo::S foo(int var = 0) = 0;
+  virtual foo::bar::S2 bar(int var = 0) = 0;
+};
+
+class D : public B {
+public:
+  foo::S foo(int var = 0) override {
+    // TODO: Implement this pure virtual method.
+    static_assert(false, "Method `foo` is not implemented.");
+  }
+
+  foo::bar::S2 bar(int var = 0) override {
+    // TODO: Implement this pure virtual method.
+    static_assert(false, "Method `bar` is not implemented.");
+  }
+};
+)cpp";
+  auto Applied = apply(Before);
+  EXPECT_EQ(Expected, Applied) << "Applied result:\n" << Applied;
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang