[clang-format] Add style option AllowShortLambdasOnASingleLine

Summary:
This option `AllowShortLambdasOnASingleLine` similar to the other `AllowShort*` options, but applied to C++ lambdas.

Reviewers: djasper, klimek

Reviewed By: klimek

Subscribers: MyDeveloperDay, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57687

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@357027 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/include/clang/Format/Format.h b/include/clang/Format/Format.h
index fd84c924ff..f9d3f03a6c 100644
--- a/include/clang/Format/Format.h
+++ b/include/clang/Format/Format.h
@@ -306,6 +306,39 @@ struct FormatStyle {
   /// If ``true``, ``if (a) return;`` can be put on a single line.
   ShortIfStyle AllowShortIfStatementsOnASingleLine;
 
+  /// Different styles for merging short lambdas containing at most one
+  /// statement.
+  enum ShortLambdaStyle {
+    /// Never merge lambdas into a single line.
+    SLS_None,
+    /// Only merge empty lambdas.
+    /// \code
+    ///   auto lambda = [](int a) {}
+    ///   auto lambda2 = [](int a) {
+    ///       return a;
+    ///   };
+    /// \endcode
+    SLS_Empty,
+    /// Merge lambda into a single line if argument of a function.
+    /// \code
+    ///   auto lambda = [](int a) {
+    ///       return a;
+    ///   };
+    ///   sort(a.begin(), a.end(), ()[] { return x < y; })
+    /// \endcode
+    SLS_Inline,
+    /// Merge all lambdas fitting on a single line.
+    /// \code
+    ///   auto lambda = [](int a) {}
+    ///   auto lambda2 = [](int a) { return a; };
+    /// \endcode
+    SLS_All,
+  };
+
+  /// Dependent on the value, ``auto lambda []() { return 0; }`` can be put on a
+  /// single line.
+  ShortLambdaStyle AllowShortLambdasOnASingleLine;
+
   /// If ``true``, ``while (true) continue;`` can be put on a single
   /// line.
   bool AllowShortLoopsOnASingleLine;
@@ -1805,6 +1838,7 @@ struct FormatStyle {
                R.AllowShortFunctionsOnASingleLine &&
            AllowShortIfStatementsOnASingleLine ==
                R.AllowShortIfStatementsOnASingleLine &&
+           AllowShortLambdasOnASingleLine == R.AllowShortLambdasOnASingleLine &&
            AllowShortLoopsOnASingleLine == R.AllowShortLoopsOnASingleLine &&
            AlwaysBreakAfterReturnType == R.AlwaysBreakAfterReturnType &&
            AlwaysBreakBeforeMultilineStrings ==