[clang-format] Introduce the flag which allows not to shrink lines

https://reviews.llvm.org/D53072

Currently there's no way to prevent to lines optimization even
if you have intentionally put <CR> to split the line.

In general case it's fine. So I would prefer to have such option
which you can enable in special cases (for me it's an IDE related use case).

Revert this change if upstream clang-format offers better solution.

Reviewed-by; Marco Bubke <marco.bubke@qt.io>

Cherry picked from commit
clang.git/fa1b9053729ec6a4425a44ec5502dd388928274a.

Change-Id: I92296dd177c811593ebba7d4b5c3c5f472af10a2
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

5 files changed, 40 insertions, 4 deletions

diff --git a/clang/include/clang/Format/Format.h b/clang/include/clang/Format/Format.h
index c424e79a971c..2574acb369fc 100644
--- a/clang/include/clang/Format/Format.h
+++ b/clang/include/clang/Format/Format.h
@@ -22,6 +22,8 @@
 #include "llvm/Support/SourceMgr.h"
 #include <system_error>
 
+#define KEEP_LINE_BREAKS_FOR_NON_EMPTY_LINES_BACKPORTED
+
 namespace llvm {
 namespace vfs {
 class FileSystem;
@@ -2467,6 +2469,16 @@ struct FormatStyle {
   bool JavaScriptWrapImports;
   // clang-format on
 
+  /// If true, no line breaks are optimized out (works only with ColumnLimit = 0)
+  /// \code
+  ///    true:                                  false:
+  ///    int foo(int a,                 vs.     int foo(int a, int b) {
+  ///            int b) {
+  ///      bar();                                 bar();
+  ///    }                                      }
+  /// \endcode
+  bool KeepLineBreaksForNonEmptyLines;
+
   /// If true, the empty line at the start of blocks is kept.
   /// \code
   ///    true:                                  false:
@@ -3457,6 +3469,7 @@ struct FormatStyle {
            JavaImportGroups == R.JavaImportGroups &&
            JavaScriptQuotes == R.JavaScriptQuotes &&
            JavaScriptWrapImports == R.JavaScriptWrapImports &&
+           KeepLineBreaksForNonEmptyLines == R.KeepLineBreaksForNonEmptyLines &&
            KeepEmptyLinesAtTheStartOfBlocks ==
                R.KeepEmptyLinesAtTheStartOfBlocks &&
            LambdaBodyIndentation == R.LambdaBodyIndentation &&
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 2b860d2a25f7..4b5d40c0eb12 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -671,6 +671,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("JavaImportGroups", Style.JavaImportGroups);
     IO.mapOptional("JavaScriptQuotes", Style.JavaScriptQuotes);
     IO.mapOptional("JavaScriptWrapImports", Style.JavaScriptWrapImports);
+    IO.mapOptional("KeepLineBreaksForNonEmptyLines",
+                   Style.KeepLineBreaksForNonEmptyLines);
     IO.mapOptional("KeepEmptyLinesAtTheStartOfBlocks",
                    Style.KeepEmptyLinesAtTheStartOfBlocks);
     IO.mapOptional("LambdaBodyIndentation", Style.LambdaBodyIndentation);
@@ -1069,6 +1071,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.TabWidth = 8;
   LLVMStyle.LambdaBodyIndentation = FormatStyle::LBI_Signature;
   LLVMStyle.MaxEmptyLinesToKeep = 1;
+  LLVMStyle.KeepLineBreaksForNonEmptyLines = false;
   LLVMStyle.KeepEmptyLinesAtTheStartOfBlocks = true;
   LLVMStyle.NamespaceIndentation = FormatStyle::NI_None;
   LLVMStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Auto;
@@ -1167,6 +1170,7 @@ FormatStyle getGoogleStyle(FormatStyle::LanguageKind Language) {
   GoogleStyle.IncludeStyle.IncludeIsMainRegex = "([-_](test|unittest))?$";
   GoogleStyle.IncludeStyle.IncludeBlocks = tooling::IncludeStyle::IBS_Regroup;
   GoogleStyle.IndentCaseLabels = true;
+  GoogleStyle.KeepLineBreaksForNonEmptyLines = false;
   GoogleStyle.KeepEmptyLinesAtTheStartOfBlocks = false;
   GoogleStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Never;
   GoogleStyle.ObjCSpaceAfterProperty = false;
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index cca85c1074de..1046aa5ff5ac 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -781,7 +781,7 @@ public:
   LineFormatter(ContinuationIndenter *Indenter, WhitespaceManager *Whitespaces,
                 const FormatStyle &Style,
                 UnwrappedLineFormatter *BlockFormatter)
-      : Indenter(Indenter), Whitespaces(Whitespaces), Style(Style),
+      : Indenter(Indenter), Style(Style), Whitespaces(Whitespaces),
         BlockFormatter(BlockFormatter) {}
   virtual ~LineFormatter() {}
 
@@ -822,7 +822,8 @@ protected:
       // assert so that we can simply call this function for all tokens.
       return true;
 
-    if (NewLine) {
+    if (NewLine || (Previous.Children[0]->First->MustBreakBefore &&
+                    Style.KeepLineBreaksForNonEmptyLines)) {
       const ParenState &P = State.Stack.back();
 
       int AdditionalIndent =
@@ -880,10 +881,10 @@ protected:
   }
 
   ContinuationIndenter *Indenter;
+  const FormatStyle &Style;
 
 private:
   WhitespaceManager *Whitespaces;
-  const FormatStyle &Style;
   UnwrappedLineFormatter *BlockFormatter;
 };
 
@@ -906,7 +907,7 @@ public:
     while (State.NextToken) {
       bool Newline =
           Indenter->mustBreak(State) ||
-          (Indenter->canBreak(State) && State.NextToken->NewlinesBefore > 0);
+          (State.NextToken->NewlinesBefore > 0 && Indenter->canBreak(State));
       unsigned Penalty = 0;
       formatChildren(State, Newline, /*DryRun=*/false, Penalty);
       Indenter->addTokenToState(State, Newline, /*DryRun=*/false);
diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 673986d16af2..f1f0f2e16f3a 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -3226,6 +3226,8 @@ void UnwrappedLineParser::nextToken(int LevelDifference) {
   else
     readTokenWithJavaScriptASI();
   FormatTok->Previous = Previous;
+  if (FormatTok->NewlinesBefore && Style.KeepLineBreaksForNonEmptyLines)
+    FormatTok->MustBreakBefore = true;
 }
 
 void UnwrappedLineParser::distributeComments(
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index c575f643b5a1..64fbc436bb5d 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -527,6 +527,22 @@ TEST_F(FormatTest, RemovesEmptyLines) {
                    "  void funk() {}\n"
                    "};",
                    Style));
+
+  Style.KeepLineBreaksForNonEmptyLines = true;
+  Style.ColumnLimit = 0;
+  EXPECT_EQ("int foo(int a,\n"
+            "        int b)\n"
+            "{\n"
+            "}",
+            format("int foo(int a,\n"
+                   "int b) {}",
+                   Style));
+
+  EXPECT_EQ("[]() {\n"
+            "  foo(); }",
+            format("[]() {\n"
+                   "foo(); }",
+                   Style));
 }
 
 TEST_F(FormatTest, RecognizesBinaryOperatorKeywords) {