[clang] [clang-format] Fix a bug in `DerivePointerAlignment: true` (PR #150744)

[Owen Pan via cfe-commits]

https://github.com/owenca updated https://github.com/llvm/llvm-project/pull/150744

>From 7418fe966ff3a3e9f3c6c431beafbdde47a1de30 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Sat, 26 Jul 2025 01:56:52 -0700
Subject: [PATCH 1/3] [clang-format] Fix a bug in `DerivePointerAlignment:
 true`

This effectively reverts a4d4859dc70c046ad928805ddeaf8fa101793394
which didn't fix the problem that `int*,` was not counted as "Left"
alignment.

Fixes #150327
---
 clang/lib/Format/Format.cpp           | 31 ++++++++++-----------------
 clang/unittests/Format/FormatTest.cpp |  7 +++++-
 2 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 1cfa3d1535902..01d2b4dfc76cc 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2641,28 +2641,19 @@ class Formatter : public TokenAnalyzer {
     int AlignmentDiff = 0;
     for (const AnnotatedLine *Line : Lines) {
       AlignmentDiff += countVariableAlignments(Line->Children);
-      for (FormatToken *Tok = Line->First; Tok && Tok->Next; Tok = Tok->Next) {
+      const auto *Prev = Line->getFirstNonComment();
+      if (!Prev)
+        break;
+      for (const auto *Tok = Prev->Next; Tok; Prev = Tok, Tok = Tok->Next) {
         if (Tok->isNot(TT_PointerOrReference))
           continue;
-        // Don't treat space in `void foo() &&` or `void() &&` as evidence.
-        if (const auto *Prev = Tok->getPreviousNonComment()) {
-          if (Prev->is(tok::r_paren) && Prev->MatchingParen) {
-            if (const auto *Func =
-                    Prev->MatchingParen->getPreviousNonComment()) {
-              if (Func->isOneOf(TT_FunctionDeclarationName, TT_StartOfName,
-                                TT_OverloadedOperator) ||
-                  Func->isTypeName(LangOpts)) {
-                continue;
-              }
-            }
-          }
-        }
-        bool SpaceBefore = Tok->hasWhitespaceBefore();
-        bool SpaceAfter = Tok->Next->hasWhitespaceBefore();
-        if (SpaceBefore && !SpaceAfter)
-          ++AlignmentDiff;
-        if (!SpaceBefore && SpaceAfter)
-          --AlignmentDiff;
+        const auto *Next = Tok->Next;
+        if (!Next)
+          break;
+        if (Prev->Tok.getIdentifierInfo())
+          AlignmentDiff += Tok->hasWhitespaceBefore() ? 1 : -1;
+        if (Next->Tok.getIdentifierInfo())
+          AlignmentDiff += Next->hasWhitespaceBefore() ? -1 : 1;
       }
     }
     return AlignmentDiff;
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index c20d099cac017..55360965d7575 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -12114,7 +12114,12 @@ TEST_F(FormatTest, UnderstandsFunctionRefQualification) {
            "void b() const &;\n";
   verifyFormat(Prefix + "int *x;", Prefix + "int* x;", DerivePointerAlignment);
 
-  verifyGoogleFormat("MACRO(int*, std::function<void() &&>);");
+  constexpr StringRef Code("MACRO(int*, std::function<void() &&>);");
+  verifyFormat(Code, DerivePointerAlignment);
+
+  auto Style = getGoogleStyle();
+  Style.DerivePointerAlignment = true;
+  verifyFormat(Code, Style);
 }
 
 TEST_F(FormatTest, PointerAlignmentFallback) {

>From d56e24b91760c1d734aff1617057618343275abc Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Sat, 26 Jul 2025 01:56:52 -0700
Subject: [PATCH 2/3] [clang-format] Fix a bug in `DerivePointerAlignment:
 true`

This effectively reverts a4d4859dc70c046ad928805ddeaf8fa101793394
which didn't fix the problem that `int*,` was not counted as "Left"
alignment.

Fixes #150327
---
 clang/lib/Format/Format.cpp | 39 +++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 38f78e80982e7..51c855c39d233 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2639,23 +2639,42 @@ class Formatter : public TokenAnalyzer {
 
   int countVariableAlignments(const SmallVectorImpl<AnnotatedLine *> &Lines) {
     int AlignmentDiff = 0;
+
     for (const AnnotatedLine *Line : Lines) {
       AlignmentDiff += countVariableAlignments(Line->Children);
-      const auto *Prev = Line->getFirstNonComment();
-      if (!Prev)
-        break;
-      for (const auto *Tok = Prev->Next; Tok; Prev = Tok, Tok = Tok->Next) {
+
+      for (const auto *Tok = Line->getFirstNonComment(); Tok; Tok = Tok->Next) {
         if (Tok->isNot(TT_PointerOrReference))
           continue;
+
+        const auto *Prev = Tok->Previous;
+        const bool PrecededByName = Prev && Prev->Tok.getIdentifierInfo();
+        const bool SpaceBefore = Tok->hasWhitespaceBefore();
+
+        // e.g. `int **`, `int*&`, etc.
+        while (Tok->Next && Tok->Next->is(TT_PointerOrReference))
+          Tok = Tok->Next;
+
         const auto *Next = Tok->Next;
-        if (!Next)
-          break;
-        if (Prev->Tok.getIdentifierInfo())
-          AlignmentDiff += Tok->hasWhitespaceBefore() ? 1 : -1;
-        if (Next->Tok.getIdentifierInfo())
-          AlignmentDiff += Next->hasWhitespaceBefore() ? -1 : 1;
+        const bool FollowedByName = Next && Next->Tok.getIdentifierInfo();
+        const bool SpaceAfter = Next && Next->hasWhitespaceBefore();
+
+        if ((!PrecededByName && !FollowedByName) ||
+            // e.g. `int * i` or `int*i`
+            (PrecededByName && FollowedByName && SpaceBefore == SpaceAfter)) {
+          continue;
+        }
+
+        if ((PrecededByName && SpaceBefore) ||
+            (FollowedByName && !SpaceAfter)) {
+          ++AlignmentDiff;
+        } else if ((PrecededByName && !SpaceBefore) ||
+                   (FollowedByName && SpaceAfter)) {
+          --AlignmentDiff;
+        }
       }
     }
+
     return AlignmentDiff;
   }
 

>From c1eb42af2684bc5e5a8175726cd18892e5ee09f3 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Sun, 27 Jul 2025 21:34:49 -0700
Subject: [PATCH 3/3] Add comments

---
 clang/lib/Format/Format.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 51c855c39d233..063780721423f 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2667,9 +2667,11 @@ class Formatter : public TokenAnalyzer {
 
         if ((PrecededByName && SpaceBefore) ||
             (FollowedByName && !SpaceAfter)) {
+          // Right alignment.
           ++AlignmentDiff;
         } else if ((PrecededByName && !SpaceBefore) ||
                    (FollowedByName && SpaceAfter)) {
+          // Left alignment.
           --AlignmentDiff;
         }
       }