[clang-format] Merge short inline function in macro definition body (#140366)

Fix #62356

Author: owenca

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -314,8 +314,8 @@ class LineJoiner {
           const AnnotatedLine *Line = nullptr;
           for (auto J = I - 1; J >= AnnotatedLines.begin(); --J) {
             assert(*J);
-            if ((*J)->InPPDirective || (*J)->isComment() ||
-                (*J)->Level > TheLine->Level) {
+            if (((*J)->InPPDirective && !(*J)->InMacroBody) ||
+                (*J)->isComment() || (*J)->Level > TheLine->Level) {
               continue;
             }
             if ((*J)->Level < TheLine->Level ||

clang/unittests/Format/FormatTest.cpp

@@ -15093,6 +15093,13 @@ TEST_F(FormatTest, PullInlineFunctionDefinitionsIntoSingleLine) {
                "};",
                MergeInlineOnly);
 
+  MergeInlineOnly.AlignEscapedNewlines = FormatStyle::ENAS_Left;
+  verifyFormat("#define Foo                \\\n"
+               "  struct S {               \\\n"
+               "    void foo() { return; } \\\n"
+               "  }",
+               MergeInlineOnly);
+
   // Also verify behavior when BraceWrapping.AfterFunction = true
   MergeInlineOnly.BreakBeforeBraces = FormatStyle::BS_Custom;
   MergeInlineOnly.BraceWrapping.AfterFunction = true;