[clang-format] allow short function body on a single line

[brandb97]

Fix issue #145161

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-format

Author: Lidong Yan (brandb97)

Changes

Fix issue #145161

---

Full diff: https://github.com/llvm/llvm-project/pull/151428.diff

4 Files Affected:

• (modified) clang/include/clang/Format/Format.h (+6)
• (modified) clang/lib/Format/Format.cpp (+3)
• (modified) clang/lib/Format/UnwrappedLineFormatter.cpp (+20)
• (modified) clang/lib/Format/UnwrappedLineParser.cpp (+4)

diff --git a/clang/include/clang/Format/Format.h b/clang/include/clang/Format/Format.h
index 31582a40de866..e13df9df83e18 100644
--- a/clang/include/clang/Format/Format.h
+++ b/clang/include/clang/Format/Format.h
@@ -878,6 +878,12 @@ struct FormatStyle {
   /// \version 3.5
   ShortFunctionStyle AllowShortFunctionsOnASingleLine;
 
+  /// Dependent on the value, function body like ``{ return 0; }`` can be
+  /// put on a single line. Only when AllowShortFunctionsOnASingleLine = None
+  /// and AllowShortBlocksOnASingleLine != Never, the value of this option
+  /// is true.
+  bool AllowShortFunctionBodiesOnASingleLine;
+
   /// Different styles for handling short if statements.
   enum ShortIfStyle : int8_t {
     /// Never put short ifs on the same line.
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 063780721423f..61c0d399ca796 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -3828,6 +3828,9 @@ reformat(const FormatStyle &Style, StringRef Code,
   default:
     break;
   }
+  Expanded.AllowShortFunctionBodiesOnASingleLine =
+      Expanded.AllowShortFunctionsOnASingleLine == FormatStyle::SFS_None &&
+      Expanded.AllowShortBlocksOnASingleLine != FormatStyle::SBS_Never;
 
   if (Expanded.DisableFormat)
     return {tooling::Replacements(), 0};
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index 0adf7ee9ed543..44c767a0db9b8 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -257,6 +257,12 @@ class LineJoiner {
       return tryMergeSimpleBlock(I, E, Limit);
     }
 
+    if (TheLine->Last->is(TT_FunctionLBrace) &&
+        TheLine->First == TheLine->Last &&
+        Style.AllowShortFunctionBodiesOnASingleLine) {
+      return tryMergeSimpleBlock(I, E, Limit);
+    }
+
     const auto *PreviousLine = I != AnnotatedLines.begin() ? I[-1] : nullptr;
     // Handle empty record blocks where the brace has already been wrapped.
     if (PreviousLine && TheLine->Last->is(tok::l_brace) &&
@@ -532,6 +538,20 @@ class LineJoiner {
       }
       return MergedLines;
     }
+
+    // Previously, UnwrappedLineParser would move the left brace to a new line
+    // when AllowShortFunctionBodiesOnASingleLine is enabled. However, if the
+    // function body cannot fit on a single line, and Style.BraceWrapping.AfterFunction
+    // is false, we should merge the function name and the left brace back onto
+    // the same line
+    if (NextLine.First->is(TT_FunctionLBrace) &&
+        Style.AllowShortFunctionBodiesOnASingleLine &&
+        !Style.BraceWrapping.AfterFunction) {
+      unsigned MergedLines = 0;
+      MergedLines = tryMergeSimpleBlock(I + 1, E, Limit);
+      return MergedLines > 0 ? 0 : 1;
+    }
+
     auto IsElseLine = [&TheLine]() -> bool {
       const FormatToken *First = TheLine->First;
       if (First->is(tok::kw_else))
diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 91b8fdc8a3c38..7dd59c1cbd678 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1921,6 +1921,10 @@ void UnwrappedLineParser::parseStructuralElement(
           }
         } else if (Style.BraceWrapping.AfterFunction) {
           addUnwrappedLine();
+        } else if (Style.AllowShortFunctionBodiesOnASingleLine) {
+          // Wrap the left brace here; we'll try to merge it back
+          // later if needed.
+          addUnwrappedLine();
         }
         if (!Previous || Previous->isNot(TT_TypeDeclarationParen))
           FormatTok->setFinalizedType(TT_FunctionLBrace);

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[HazardyKnusperkeks]

You are missing unit tests. clang/unittests/Format/FromatTest.cpp.

[HazardyKnusperkeks]

Why is this needed? It seems wrong to me.

[brandb97]

If Style.AllowShortFunctionBodiesOnSingleLine = true, I modified UnwrappedLineParser to parse

int main() {
  //...
}

into unwrapped lines ["int main()", "{", ..., "}"], not ["int main() {", ..., "}"] as usual. If clang-format can't put function body on a single line, I want to merge "int main()" and "{" back if possible.

[brandb97]

The reason I parse the { in void foo() { as an unwrapped line is to allow merging the { and the function body into one line when the function body is very short.