clang-format 19 idempotent regression from 18 for #define within a function

[JohnC32]

Running clang-format 19.1.4 twice produces different results when we have #define statements within an initializer. Running with clang-format 18.1.1 shows no difference on repeated invocations.

Given idempotent_define.cpp

namespace Foo {
void foo() {
#define GEN_ID(_x) \
    char const *_x {    \
        #_x              \
    }
    GEN_ID(one);
    GEN_ID(two);
}
}

using _clang-format:

---
BasedOnStyle: Google
IndentWidth: 4
ColumnLimit: 100
...

clang-format 19.1.4 yields the following differences on successive runs. Notice that define flips between being on a single line and multiple lines.

/path/to/llvm-19.1.4/bin/clang-format -style=file idempotent_define.cpp >out.19.1.4.a.cpp 2>&1
/path/to/llvm-19.1.4/bin/clang-format -style=file out.19.1.4.a.cpp >out.19.1.4.b.cpp 2>&1
/path/to/llvm-19.1.4/bin/clang-format -style=file out.19.1.4.b.cpp >out.19.1.4.c.cpp 2>&1

diff -u out.19.1.4.a.cpp out.19.1.4.b.cpp
--- out.19.1.4.a.cpp	2024-12-02 13:24:50.702497070 -0500
+++ out.19.1.4.b.cpp	2024-12-02 13:24:50.714497177 -0500
@@ -1,6 +1,7 @@
 namespace Foo {
 void foo() {
-#define GEN_ID(_x) char const *_x{#_x}
+#define GEN_ID(_x) \
+    char const *_x { #_x }
     GEN_ID(one);
     GEN_ID(two);
 }
diff -u out.19.1.4.b.cpp out.19.1.4.c.cpp
--- out.19.1.4.b.cpp	2024-12-02 13:24:50.714497177 -0500
+++ out.19.1.4.c.cpp	2024-12-02 13:24:50.733497347 -0500
@@ -1,7 +1,6 @@
 namespace Foo {
 void foo() {
-#define GEN_ID(_x) \
-    char const *_x { #_x }
+#define GEN_ID(_x) char const *_x{#_x}
     GEN_ID(one);
     GEN_ID(two);
 }
diff -u out.19.1.4.a.cpp out.19.1.4.c.cpp

[owenca]

Bisected it to commit ee23599. IMO this is not a regression because the l_brace above #_x was already incorrectly annotated as FunctionLBrace before the commit.

[owenca]

/cherry-pick 54ca1c4

[llvmbot]

/pull-request #119503