https://github.com/Lane0218 updated 
https://github.com/llvm/llvm-project/pull/189024

>From 04fa0e42a1ddb54251279f9e7224beb39db6e8a7 Mon Sep 17 00:00:00 2001
From: Lane0218 <[email protected]>
Date: Fri, 27 Mar 2026 23:15:04 +0800
Subject: [PATCH] [clang-format] Fix spacing before :: after non-macro
 identifiers

Preserve spaces before :: only for identifiers that likely name
object-like macros, and otherwise format identifier :: as identifier::.

This fixes clang-format leaving dependent nested name specifiers such as
&T :: member half-formatted as &T ::member.

Implement the macro heuristic as a shared FormatToken helper so both
QualifierAlignmentFixer and TokenAnnotator use the same logic. Allow the
TokenAnnotator call site to treat identifiers followed by :: as possible
macros for cases such as ALWAYS_INLINE ::std::string.

Add a regression test for the reported case while keeping the existing
ALWAYS_INLINE ::std::string coverage.

Fixes #188754
---
 clang/lib/Format/FormatToken.h                | 27 +++++++++++++++++
 clang/lib/Format/QualifierAlignmentFixer.cpp  | 29 ++-----------------
 clang/lib/Format/QualifierAlignmentFixer.h    |  3 --
 clang/lib/Format/TokenAnnotator.cpp           |  7 ++---
 clang/unittests/Format/FormatTest.cpp         |  2 ++
 clang/unittests/Format/QualifierFixerTest.cpp | 12 ++++----
 6 files changed, 40 insertions(+), 40 deletions(-)

diff --git a/clang/lib/Format/FormatToken.h b/clang/lib/Format/FormatToken.h
index ba9a95440f0c2..028ef440e689f 100644
--- a/clang/lib/Format/FormatToken.h
+++ b/clang/lib/Format/FormatToken.h
@@ -875,6 +875,33 @@ struct FormatToken {
     return Tok;
   }
 
+  /// Returns \c true if this token likely names an object-like macro.
+  ///
+  /// If \p AllowFollowingColonColon is \c true, a following \c :: does not
+  /// disqualify the token from being considered macro-like.
+  bool isPossibleMacro(bool AllowFollowingColonColon = false) const {
+    if (isNot(tok::identifier))
+      return false;
+
+    assert(!TokenText.empty());
+
+    // T, K, U, V likely could be template arguments.
+    if (TokenText.size() == 1)
+      return false;
+
+    // It's unlikely that qualified names are object-like macros.
+    const auto *Prev = getPreviousNonComment();
+    if (Prev && Prev->is(tok::coloncolon))
+      return false;
+    if (!AllowFollowingColonColon) {
+      const auto *Next = getNextNonComment();
+      if (Next && Next->is(tok::coloncolon))
+        return false;
+    }
+
+    return TokenText == TokenText.upper();
+  }
+
   /// Returns \c true if this token ends a block indented initializer list.
   [[nodiscard]] bool isBlockIndentedInitRBrace(const FormatStyle &Style) const;
 
diff --git a/clang/lib/Format/QualifierAlignmentFixer.cpp 
b/clang/lib/Format/QualifierAlignmentFixer.cpp
index eb0f886fc8459..60f2958101c71 100644
--- a/clang/lib/Format/QualifierAlignmentFixer.cpp
+++ b/clang/lib/Format/QualifierAlignmentFixer.cpp
@@ -273,7 +273,7 @@ const FormatToken 
*LeftRightQualifierAlignmentFixer::analyzeRight(
     return Tok;
 
   // Stay safe and don't move past macros, also don't bother with sorting.
-  if (isPossibleMacro(TypeToken))
+  if (TypeToken->isPossibleMacro())
     return Tok;
 
   // The case `const long long int volatile` -> `long long int const volatile`
@@ -410,7 +410,7 @@ const FormatToken 
*LeftRightQualifierAlignmentFixer::analyzeLeft(
   }
 
   // Stay safe and don't move past macros, also don't bother with sorting.
-  if (isPossibleMacro(TypeToken))
+  if (TypeToken->isPossibleMacro())
     return Tok;
 
   // Examples given in order of ['const', 'volatile', 'type']
@@ -641,30 +641,5 @@ bool isConfiguredQualifierOrType(const FormatToken *Tok,
                  isConfiguredQualifier(Tok, Qualifiers));
 }
 
-// If a token is an identifier and it's upper case, it could
-// be a macro and hence we need to be able to ignore it.
-bool isPossibleMacro(const FormatToken *Tok) {
-  assert(Tok);
-  if (Tok->isNot(tok::identifier))
-    return false;
-
-  const auto Text = Tok->TokenText;
-  assert(!Text.empty());
-
-  // T,K,U,V likely could be template arguments
-  if (Text.size() == 1)
-    return false;
-
-  // It's unlikely that qualified names are object-like macros.
-  const auto *Prev = Tok->getPreviousNonComment();
-  if (Prev && Prev->is(tok::coloncolon))
-    return false;
-  const auto *Next = Tok->getNextNonComment();
-  if (Next && Next->is(tok::coloncolon))
-    return false;
-
-  return Text == Text.upper();
-}
-
 } // namespace format
 } // namespace clang
diff --git a/clang/lib/Format/QualifierAlignmentFixer.h 
b/clang/lib/Format/QualifierAlignmentFixer.h
index a0a0d597ebf30..09fcd7b943e67 100644
--- a/clang/lib/Format/QualifierAlignmentFixer.h
+++ b/clang/lib/Format/QualifierAlignmentFixer.h
@@ -38,9 +38,6 @@ bool isConfiguredQualifierOrType(const FormatToken *Tok,
                                  const std::vector<tok::TokenKind> &Qualifiers,
                                  const LangOptions &LangOpts);
 
-// Is the Token likely a Macro
-bool isPossibleMacro(const FormatToken *Tok);
-
 class LeftRightQualifierAlignmentFixer : public TokenAnalyzer {
   std::string Qualifier;
   bool RightAlign;
diff --git a/clang/lib/Format/TokenAnnotator.cpp 
b/clang/lib/Format/TokenAnnotator.cpp
index d2cdc28a7da7b..aba7753a5572e 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -5646,10 +5646,9 @@ bool TokenAnnotator::spaceRequiredBefore(const 
AnnotatedLine &Line,
     return false;
   }
   if (Right.is(tok::coloncolon) && Left.is(tok::identifier)) {
-    // Generally don't remove existing spaces between an identifier and "::".
-    // The identifier might actually be a macro name such as ALWAYS_INLINE. If
-    // this turns out to be too lenient, add analysis of the identifier itself.
-    return Right.hasWhitespaceBefore();
+    // Preserve the space in constructs such as ALWAYS_INLINE ::std::string.
+    return Left.isPossibleMacro(/*AllowFollowingColonColon=*/true) &&
+           Right.hasWhitespaceBefore();
   }
   if (Right.is(tok::coloncolon) &&
       Left.isNoneOf(tok::l_brace, tok::comment, tok::l_paren)) {
diff --git a/clang/unittests/Format/FormatTest.cpp 
b/clang/unittests/Format/FormatTest.cpp
index 2701a7fca7346..6cb28f2c98c2a 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -80,6 +80,8 @@ TEST_F(FormatTest, NestedNameSpecifiers) {
   verifyFormat("static constexpr bool Bar = _Atomic(bar())::value;");
   verifyFormat("bool a = 2 < ::SomeFunction();");
   verifyFormat("ALWAYS_INLINE ::std::string getName();");
+  verifyFormat("template <typename T> auto mem = &T::member;",
+               "template <typename T> auto mem = &T :: member;");
   verifyFormat("some::string getName();");
 }
 
diff --git a/clang/unittests/Format/QualifierFixerTest.cpp 
b/clang/unittests/Format/QualifierFixerTest.cpp
index 7ff426d490eab..3ee1ecc9df851 100644
--- a/clang/unittests/Format/QualifierFixerTest.cpp
+++ b/clang/unittests/Format/QualifierFixerTest.cpp
@@ -1126,15 +1126,15 @@ TEST_F(QualifierFixerTest, IsQualifierType) {
 TEST_F(QualifierFixerTest, IsMacro) {
   auto Tokens = annotate("INT INTPR Foo int");
   ASSERT_EQ(Tokens.size(), 5u) << Tokens;
-  EXPECT_TRUE(isPossibleMacro(Tokens[0]));
-  EXPECT_TRUE(isPossibleMacro(Tokens[1]));
-  EXPECT_FALSE(isPossibleMacro(Tokens[2]));
-  EXPECT_FALSE(isPossibleMacro(Tokens[3]));
+  EXPECT_TRUE(Tokens[0]->isPossibleMacro());
+  EXPECT_TRUE(Tokens[1]->isPossibleMacro());
+  EXPECT_FALSE(Tokens[2]->isPossibleMacro());
+  EXPECT_FALSE(Tokens[3]->isPossibleMacro());
 
   Tokens = annotate("FOO::BAR");
   ASSERT_EQ(Tokens.size(), 4u) << Tokens;
-  EXPECT_FALSE(isPossibleMacro(Tokens[0]));
-  EXPECT_FALSE(isPossibleMacro(Tokens[2]));
+  EXPECT_FALSE(Tokens[0]->isPossibleMacro());
+  EXPECT_FALSE(Tokens[2]->isPossibleMacro());
 }
 
 TEST_F(QualifierFixerTest, OverlappingQualifier) {

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