[clang] [clang-format] Fix short functions with nested braced-init (PR #213550)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-format

Author: Gauarv Chaudhary (ANAMASGARD)

<details>
<summary>Changes</summary>

Fixes #<!-- -->213286.

  Keep short functions on one line when their return statement contains nested braced initializers.

  The closing brace now checks the kind of its matching opening brace, so braced-init lists are allowed while structural
  braces still prevent merging.

  Tests:
  - `FormatTest.CustomShortFunctionOptions`
  - `FormatTest.AllowShortRecordOnASingleLine`
  - full `FormatTests` suite (1275 passed)

---
Full diff: https://github.com/llvm/llvm-project/pull/213550.diff


2 Files Affected:

- (modified) clang/lib/Format/UnwrappedLineFormatter.cpp (+8-4) 
- (modified) clang/unittests/Format/FormatTest.cpp (+1) 


``````````diff
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index 7ea424349d923..7afc7a46dd1c0 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -983,13 +983,17 @@ class LineJoiner {
         if (!nextTwoLinesFitInto(I, Limit))
           return 0;
 
-        // Second, check that the next line does not contain any braces - if it
-        // does, readability declines when putting it into a single line.
+        // Second, check that the next line does not contain non-braced-init
+        // braces - if it does, readability declines when putting it into a
+        // single line.
         if (I[1]->Last->is(TT_LineComment))
           return 0;
         do {
-          if (Tok->isOneOf(tok::l_brace, tok::r_brace) &&
-              Tok->isNot(BK_BracedInit)) {
+          if (Tok->is(tok::l_brace) && Tok->isNot(BK_BracedInit))
+            return 0;
+          if (Tok->is(tok::r_brace) &&
+              (!Tok->MatchingParen ||
+               Tok->MatchingParen->isNot(BK_BracedInit))) {
             return 0;
           }
           Tok = Tok->Next;
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index b72a683ac1fff..6f604167f785c 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -15368,6 +15368,7 @@ TEST_F(FormatTest, CustomShortFunctionOptions) {
   // All functions should be on a single line if they fit
   verifyFormat("int f() { return 42; }", CustomAll);
   verifyFormat("int g() { return f() + h(); }", CustomAll);
+  verifyFormat("pair<int, int> g() { return {1, {}}; }", CustomAll);
   verifyFormat("class C {\n"
                "  int f() { return 42; }\n"
                "};",

``````````

</details>


https://github.com/llvm/llvm-project/pull/213550