[clang] [clang-format] Fix a bug in merging short inline functions (PR #203754)

[via cfe-commits]

https://github.com/owenca created https://github.com/llvm/llvm-project/pull/203754

Fixes #203209

>From 510dae3308c624d5d0a754cff8570fd844b46777 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Sun, 14 Jun 2026 02:05:22 -0700
Subject: [PATCH] [clang-format] Fix a bug in merging short inline functions

Fixes #203209
---
 clang/lib/Format/UnwrappedLineFormatter.cpp | 22 ++++++++++-----------
 clang/unittests/Format/FormatTest.cpp       |  9 +++++++++
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index 42eabc065b1a8..29cc0e3149e2b 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -314,8 +314,7 @@ class LineJoiner {
       }
     }
 
-    auto ShouldMergeShortFunctions = [this, &I, &NextLine, PreviousLine,
-                                      TheLine]() {
+    auto ShouldMergeShortFunctions = [&] {
       if (Style.AllowShortFunctionsOnASingleLine.isAll())
         return true;
 
@@ -331,7 +330,7 @@ class LineJoiner {
         if (Style.isJavaScript() && TheLine->Last->is(TT_FunctionLBrace))
           return true;
 
-        if (TheLine->Level != 0) {
+        if (const auto Level = TheLine->Level; Level != 0) {
           if (!PreviousLine)
             return false;
 
@@ -339,15 +338,16 @@ class LineJoiner {
           // Find the last line with lower level.
           const AnnotatedLine *Line = nullptr;
           for (auto J = I - 1; J >= AnnotatedLines.begin(); --J) {
-            assert(*J);
-            if (((*J)->InPPDirective && !(*J)->InMacroBody) ||
-                (*J)->isComment() || (*J)->Level > TheLine->Level) {
+            const auto *L = *J;
+            assert(L);
+            if (TheLine->InMacroBody && !L->InMacroBody)
+              break;
+            if (L->isComment() || (!TheLine->InPPDirective && L->InPPDirective))
               continue;
-            }
-            if ((*J)->Level < TheLine->Level ||
-                (Style.BreakBeforeBraces == FormatStyle::BS_Whitesmiths &&
-                 (*J)->First->is(tok::l_brace))) {
-              Line = *J;
+            if (L->Level < Level ||
+                (L->Level == Level && L->First->is(tok::l_brace) &&
+                 Style.BreakBeforeBraces == FormatStyle::BS_Whitesmiths)) {
+              Line = L;
               break;
             }
           }
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 6e1150227c452..9a73abe6c88c0 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -15421,6 +15421,15 @@ TEST_F(FormatTest, PullInlineOnlyFunctionDefinitionsIntoSingleLine) {
                "}",
                MergeInlineOnly);
 
+  MergeInlineOnly.NamespaceIndentation = FormatStyle::NI_All;
+  verifyFormat("namespace {\n"
+               "  class Class {\n"
+               "#define MACRO 1\n"
+               "    int f() { return 1; }\n"
+               "  };\n"
+               "} // namespace",
+               MergeInlineOnly);
+
   MergeInlineOnly.BreakBeforeBraces = FormatStyle::BS_Whitesmiths;
   verifyFormat("class Foo\n"
                "  {\n"