[clang-format] Fix AllowShortLambdasOnASingleLine interfering with lambda brace wrapping.

[rmarker]

Fix an issue where the lambda body left brace could sometimes fail to be wrapped when AllowShortLambdasOnASingleLine is enabled.

Now, when BraceWrapping.BeforeLambdaBody is enabled, if the brace is not wrapped, we prevent breaks in the lambda body.

Resolves #81845

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: None (rmarker)

Changes

Fix an issue where the lambda body left brace could sometimes fail to be wrapped when AllowShortLambdasOnASingleLine is enabled.

Now, when BraceWrapping.BeforeLambdaBody is enabled, if the brace is not wrapped, we prevent breaks in the lambda body.

Resolves #81845

---

Full diff: https://github.com/llvm/llvm-project/pull/81848.diff

3 Files Affected:

• (modified) clang/lib/Format/ContinuationIndenter.cpp (+12-4)
• (modified) clang/lib/Format/ContinuationIndenter.h (+1-1)
• (modified) clang/unittests/Format/FormatTest.cpp (+13)

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 159d130cb67332..96e9684409c744 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -1794,7 +1794,7 @@ void ContinuationIndenter::moveStatePastScopeOpener(LineState &State,
   }
 
   if (Current.MatchingParen && Current.is(BK_Block)) {
-    moveStateToNewBlock(State);
+    moveStateToNewBlock(State, Newline);
     return;
   }
 
@@ -1981,7 +1981,7 @@ void ContinuationIndenter::moveStatePastScopeCloser(LineState &State) {
   }
 }
 
-void ContinuationIndenter::moveStateToNewBlock(LineState &State) {
+void ContinuationIndenter::moveStateToNewBlock(LineState &State, bool NewLine) {
   if (Style.LambdaBodyIndentation == FormatStyle::LBI_OuterScope &&
       State.NextToken->is(TT_LambdaLBrace) &&
       !State.Line->MightBeFunctionDecl) {
@@ -1993,10 +1993,18 @@ void ContinuationIndenter::moveStateToNewBlock(LineState &State) {
       NestedBlockIndent + (State.NextToken->is(TT_ObjCBlockLBrace)
                                ? Style.ObjCBlockIndentWidth
                                : Style.IndentWidth);
+
+  // Even when wrapping before lambda body, the left brace can still be added to
+  // the same line. This occurs when checking whether the whole lambda body can
+  // go on a single line. In this case we have to make sure there are no line
+  // breaks in the body, otherwise we could just end up with a regular lambda
+  // body without the brace wrapped.
+  bool NoLineBreak = Style.BraceWrapping.BeforeLambdaBody && !NewLine &&
+                     State.NextToken->is(TT_LambdaLBrace);
+
   State.Stack.push_back(ParenState(State.NextToken, NewIndent,
                                    State.Stack.back().LastSpace,
-                                   /*AvoidBinPacking=*/true,
-                                   /*NoLineBreak=*/false));
+                                   /*AvoidBinPacking=*/true, NoLineBreak));
   State.Stack.back().NestedBlockIndent = NestedBlockIndent;
   State.Stack.back().BreakBeforeParameter = true;
 }
diff --git a/clang/lib/Format/ContinuationIndenter.h b/clang/lib/Format/ContinuationIndenter.h
index 057b85bd32d505..2598947bb624c5 100644
--- a/clang/lib/Format/ContinuationIndenter.h
+++ b/clang/lib/Format/ContinuationIndenter.h
@@ -104,7 +104,7 @@ class ContinuationIndenter {
   /// Update 'State' according to the next token being one of ")>}]".
   void moveStatePastScopeCloser(LineState &State);
   /// Update 'State' with the next token opening a nested block.
-  void moveStateToNewBlock(LineState &State);
+  void moveStateToNewBlock(LineState &State, bool NewLine);
 
   /// Reformats a raw string literal.
   ///
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index b0687eaecb10fe..b33613bf143170 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -22893,6 +22893,19 @@ TEST_F(FormatTest, FormatsLambdas) {
                LLVMWithBeforeLambdaBody);
   verifyFormat("FctWithTwoParams_SLS_All([]() { return 43; }, 87);",
                LLVMWithBeforeLambdaBody);
+  verifyFormat(
+      "FctWithTwoParams_SLS_All(\n"
+      "    87, []() { return LongLineThatWillForceBothParamsToNewLine(); });\n",
+      LLVMWithBeforeLambdaBody);
+  verifyFormat(
+      "FctWithTwoParams_SLS_All(\n"
+      "    87,\n"
+      "    []()\n"
+      "    {\n"
+      "      return "
+      "LongLineThatWillForceTheLambdaBodyToBeBrokenIntoMultipleLines();\n"
+      "    });",
+      LLVMWithBeforeLambdaBody);
   verifyFormat("FctWithOneNestedLambdas_SLS_All([]() { return 17; });",
                LLVMWithBeforeLambdaBody);
   verifyFormat(