[clang-format] Fix AllowShortLambdasOnASingleLine interfering with lambda brace wrapping. (#81848)

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

Author: rmarker

clang/lib/Format/ContinuationIndenter.cpp

@@ -1803,7 +1803,7 @@ void ContinuationIndenter::moveStatePastScopeOpener(LineState &State,
   }
 
   if (Current.MatchingParen && Current.is(BK_Block)) {
-    moveStateToNewBlock(State);
+    moveStateToNewBlock(State, Newline);
     return;
   }
 
@@ -1991,7 +1991,7 @@ 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) {
@@ -2003,10 +2003,18 @@ 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;
 }

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.
   ///

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(); });",
+      LLVMWithBeforeLambdaBody);
+  verifyFormat(
+      "FctWithTwoParams_SLS_All(\n"
+      "    87,\n"
+      "    []()\n"
+      "    {\n"
+      "      return "
+      "LongLineThatWillForceTheLambdaBodyToBeBrokenIntoMultipleLines();\n"
+      "    });",
+      LLVMWithBeforeLambdaBody);
   verifyFormat("FctWithOneNestedLambdas_SLS_All([]() { return 17; });",
                LLVMWithBeforeLambdaBody);
   verifyFormat(