clang-format: remove trailing lines in lamdas and arrow functions.

Summary:
clang-format already removes empty lines at the beginning & end of
blocks:

    int x() {

      foo();  // lines before and after will be removed.

    }

However because lamdas and arrow functions are parsed as expressions,
the existing logic to remove empty lines in UnwrappedLineFormatter
doesn't handle them.

This change special cases arrow functions in ContinuationIndenter to
remove empty lines:

    x = []() {

      foo();  // lines before and after will now be removed.

    };

Reviewers: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D40178

llvm-svn: 318537

2 files changed, 14 insertions, 1 deletions

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 3fed32f6f4c..44e6ad4232e 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -701,8 +701,18 @@ unsigned ContinuationIndenter::addTokenOnNewLine(LineState &State,
     State.Stack.back().BreakBeforeParameter = false;
 
   if (!DryRun) {
+    unsigned MaxEmptyLinesToKeep = Style.MaxEmptyLinesToKeep + 1;
+    if (Current.is(tok::r_brace) && Current.MatchingParen &&
+        // Only strip trailing empty lines for l_braces that have children, i.e.
+        // for function expressions (lambdas, arrows, etc).
+        !Current.MatchingParen->Children.empty()) {
+      // lambdas and arrow functions are expressions, thus their r_brace is not
+      // on its own line, and thus not covered by UnwrappedLineFormatter's logic
+      // about removing empty lines on closing blocks. Special case them here.
+      MaxEmptyLinesToKeep = 1;
+    }
     unsigned Newlines = std::max(
-        1u, std::min(Current.NewlinesBefore, Style.MaxEmptyLinesToKeep + 1));
+        1u, std::min(Current.NewlinesBefore, MaxEmptyLinesToKeep));
     bool ContinuePPDirective =
         State.Line->InPPDirective && State.Line->Type != LT_ImportStatement;
     Whitespaces.replaceWhitespace(Current, Newlines, State.Column, State.Column,
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index a82cd5abe27..2e9d803a191 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -1117,6 +1117,9 @@ void UnwrappedLineFormatter::formatFirstToken(const AnnotatedLine &Line,
       (!RootToken.Next ||
        (RootToken.Next->is(tok::semi) && !RootToken.Next->Next)))
     Newlines = std::min(Newlines, 1u);
+  // Remove empty lines at the start of nested blocks (lambdas/arrow functions)
+  if (PreviousLine == nullptr && Line.Level > 0)
+    Newlines = std::min(Newlines, 1u);
   if (Newlines == 0 && !RootToken.IsFirst)
     Newlines = 1;
   if (RootToken.IsFirst && !RootToken.HasUnescapedNewline)