[clang-format] Stop moving lambda to new line only to indent it more.

Hanging indents are minimised for lambdas by pushing them onto a new
line. However, it could still do this even if it would cause even more
hanging indents than it otherwise would.

The handling has been expanded to check for this case and avoid moving
the lambda to a new line.

Author: rmarker

clang/lib/Format/ContinuationIndenter.cpp

@@ -325,13 +325,30 @@ bool ContinuationIndenter::canBreak(const LineState &State) {
   if (Current.isMemberAccess() && CurrentState.ContainsUnwrappedBuilder)
     return false;
 
-  // Don't create a 'hanging' indent if there are multiple blocks in a single
-  // statement and we are aligning lambda blocks to their signatures.
-  if (Previous.is(tok::l_brace) && State.Stack.size() > 1 &&
+  // Force a lambda onto a new line so that we don't create a 'hanging' indent
+  // if there are multiple blocks in a single statement and we are aligning
+  // lambda blocks to their signatures.
+  if (Previous.is(tok::l_brace) && State.Stack.size() > 2 &&
       State.Stack[State.Stack.size() - 2].NestedBlockInlined &&
       State.Stack[State.Stack.size() - 2].HasMultipleNestedBlocks &&
       Style.LambdaBodyIndentation == FormatStyle::LBI_Signature) {
-    return false;
+    if (!Style.isCpp())
+      return false;
+
+    // Make sure to push lambdas to a new line when they are an argument with
+    // other arguments preceding them.
+    if (State.Stack[State.Stack.size() - 2].StartOfFunctionCall > 0)
+      return false;
+
+    // Only force a new line if it is not just going to create a worse hanging
+    // indent. Otherwise, based on the ContinuationIndentWidth, we could end up
+    // more indented than we would've been. To avoid odd looking breaks, make
+    // sure we save at least IndentWidth.
+    if (State.Stack[State.Stack.size() - 3].Indent +
+            Style.ContinuationIndentWidth + Style.IndentWidth <
+        State.Stack[State.Stack.size() - 2].Indent) {
+      return false;
+    }
   }
 
   // Don't break after very short return types (e.g. "void") as that is often

clang/unittests/Format/FormatTest.cpp

@@ -23814,6 +23814,20 @@ TEST_F(FormatTest, FormatsLambdas) {
                "}",
                LLVMWithBeforeLambdaBody);
 
+  // Make sure we don't put the lambda on a new line when it would be indented
+  // more than where it would be otherwise.
+  verifyFormat("if ([]()\n"
+               "    {\n"
+               "      return true;\n"
+               "    }()) {\n"
+               "}",
+               LLVMWithBeforeLambdaBody);
+  verifyFormat("fun([]()\n"
+               "    {\n"
+               "      return 17;\n"
+               "    });",
+               LLVMWithBeforeLambdaBody);
+
   LLVMWithBeforeLambdaBody.AllowShortLambdasOnASingleLine =
       FormatStyle::ShortLambdaStyle::SLS_Empty;
   verifyFormat("FctWithOneNestedLambdaInline_SLS_Empty(\n"