[clang-format] Add ability to wrap braces after multi-line control statements

Summary:
Change the BraceWrappingFlags' AfterControlStatement from a bool to an enum with three values:

* "Never": This is the default, and does not do any brace wrapping after control statements.
* "MultiLine": This only wraps braces after multi-line control statements (this really only happens when a ColumnLimit is specified).
* "Always": This always wraps braces after control statements.

The first and last options are backwards-compatible with "false" and "true", respectively.

The new "MultiLine" option is useful for when a wrapped control statement's indentation matches the subsequent block's indentation. It makes it easier to see at a glance where the control statement ends and where the block's code begins. For example:

```
if (
  foo
  && bar )
{
  baz();
}
```

vs.

```
if (
  foo
  && bar ) {
  baz();
}
```

Short control statements (1 line) do not wrap the brace to the next line, e.g.

```
if (foo) {
  bar();
} else {
  baz();
}
```

Reviewers: sammccall, owenpan, reuk, MyDeveloperDay, klimek

Reviewed By: MyDeveloperDay

Subscribers: MyDeveloperDay, cfe-commits

Patch By: mitchell-stellar

Tags: #clang-format, #clang, #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D68296

llvm-svn: 373647

3 files changed, 78 insertions, 21 deletions

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index dd561cc0d89..5b267784ff1 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -182,6 +182,20 @@ template <> struct ScalarEnumerationTraits<FormatStyle::BraceBreakingStyle> {
 };
 
 template <>
+struct ScalarEnumerationTraits<
+    FormatStyle::BraceWrappingAfterControlStatementStyle> {
+  static void
+  enumeration(IO &IO,
+              FormatStyle::BraceWrappingAfterControlStatementStyle &Value) {
+    IO.enumCase(Value, "false", FormatStyle::BWACS_Never);
+    IO.enumCase(Value, "true", FormatStyle::BWACS_Always);
+    IO.enumCase(Value, "Never", FormatStyle::BWACS_Never);
+    IO.enumCase(Value, "MultiLine", FormatStyle::BWACS_MultiLine);
+    IO.enumCase(Value, "Always", FormatStyle::BWACS_Always);
+  }
+};
+
+template <>
 struct ScalarEnumerationTraits<FormatStyle::BreakConstructorInitializersStyle> {
   static void
   enumeration(IO &IO, FormatStyle::BreakConstructorInitializersStyle &Value) {
@@ -629,9 +643,12 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
   if (Style.BreakBeforeBraces == FormatStyle::BS_Custom)
     return Style;
   FormatStyle Expanded = Style;
-  Expanded.BraceWrapping = {false, false, false, false, false, false,
-                            false, false, false, false, false, false,
-                            false, true,  true,  true};
+  Expanded.BraceWrapping = {false, false, FormatStyle::BWACS_Never,
+                            false, false, false,
+                            false, false, false,
+                            false, false, false,
+                            false, true,  true,
+                            true};
   switch (Style.BreakBeforeBraces) {
   case FormatStyle::BS_Linux:
     Expanded.BraceWrapping.AfterClass = true;
@@ -656,7 +673,7 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
   case FormatStyle::BS_Allman:
     Expanded.BraceWrapping.AfterCaseLabel = true;
     Expanded.BraceWrapping.AfterClass = true;
-    Expanded.BraceWrapping.AfterControlStatement = true;
+    Expanded.BraceWrapping.AfterControlStatement = FormatStyle::BWACS_Always;
     Expanded.BraceWrapping.AfterEnum = true;
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterNamespace = true;
@@ -670,7 +687,7 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
   case FormatStyle::BS_Whitesmiths:
     Expanded.BraceWrapping.AfterCaseLabel = true;
     Expanded.BraceWrapping.AfterClass = true;
-    Expanded.BraceWrapping.AfterControlStatement = true;
+    Expanded.BraceWrapping.AfterControlStatement = FormatStyle::BWACS_Always;
     Expanded.BraceWrapping.AfterEnum = true;
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterNamespace = true;
@@ -681,8 +698,12 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
     Expanded.BraceWrapping.BeforeElse = true;
     break;
   case FormatStyle::BS_GNU:
-    Expanded.BraceWrapping = {true, true, true, true, true, true, true, true,
-                              true, true, true, true, true, true, true, true};
+    Expanded.BraceWrapping = {true, true, FormatStyle::BWACS_Always,
+                              true, true, true,
+                              true, true, true,
+                              true, true, true,
+                              true, true, true,
+                              true};
     break;
   case FormatStyle::BS_WebKit:
     Expanded.BraceWrapping.AfterFunction = true;
@@ -722,9 +743,12 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.BreakBeforeBinaryOperators = FormatStyle::BOS_None;
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
-  LLVMStyle.BraceWrapping = {false, false, false, false, false, false,
-                             false, false, false, false, false, false,
-                             false, true,  true,  true};
+  LLVMStyle.BraceWrapping = {false, false, FormatStyle::BWACS_Never,
+                             false, false, false,
+                             false, false, false,
+                             false, false, false,
+                             false, true,  true,
+                             true};
   LLVMStyle.BreakAfterJavaFieldAnnotations = false;
   LLVMStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeColon;
   LLVMStyle.BreakInheritanceList = FormatStyle::BILS_BeforeColon;
@@ -1067,7 +1091,7 @@ FormatStyle getMicrosoftStyle(FormatStyle::LanguageKind Language) {
   Style.UseTab = FormatStyle::UT_Never;
   Style.BreakBeforeBraces = FormatStyle::BS_Custom;
   Style.BraceWrapping.AfterClass = true;
-  Style.BraceWrapping.AfterControlStatement = true;
+  Style.BraceWrapping.AfterControlStatement = FormatStyle::BWACS_Always;
   Style.BraceWrapping.AfterEnum = true;
   Style.BraceWrapping.AfterFunction = true;
   Style.BraceWrapping.AfterNamespace = true;
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index df30f7db80e..8b8d357d9cb 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -306,8 +306,24 @@ private:
     }
     // Try to merge a control statement block with left brace wrapped
     if (I[1]->First->is(tok::l_brace) &&
-        TheLine->First->isOneOf(tok::kw_if, tok::kw_while, tok::kw_for)) {
-      return Style.BraceWrapping.AfterControlStatement
+        (TheLine->First->isOneOf(tok::kw_if, tok::kw_while, tok::kw_for,
+                                 tok::kw_switch, tok::kw_try, tok::kw_do) ||
+         (TheLine->First->is(tok::r_brace) && TheLine->First->Next &&
+          TheLine->First->Next->isOneOf(tok::kw_else, tok::kw_catch))) &&
+        Style.BraceWrapping.AfterControlStatement ==
+            FormatStyle::BWACS_MultiLine) {
+      // If possible, merge the next line's wrapped left brace with the current
+      // line. Otherwise, leave it on the next line, as this is a multi-line
+      // control statement.
+      return (Style.ColumnLimit == 0 ||
+              TheLine->Last->TotalLength <= Style.ColumnLimit)
+                 ? 1
+                 : 0;
+    } else if (I[1]->First->is(tok::l_brace) &&
+               TheLine->First->isOneOf(tok::kw_if, tok::kw_while,
+                                       tok::kw_for)) {
+      return (Style.BraceWrapping.AfterControlStatement ==
+              FormatStyle::BWACS_Always)
                  ? tryMergeSimpleBlock(I, E, Limit)
                  : 0;
     }
@@ -410,7 +426,8 @@ private:
       SmallVectorImpl<AnnotatedLine *>::const_iterator E, unsigned Limit) {
     if (Limit == 0)
       return 0;
-    if (Style.BraceWrapping.AfterControlStatement &&
+    if (Style.BraceWrapping.AfterControlStatement ==
+            FormatStyle::BWACS_Always &&
         I[1]->First->is(tok::l_brace) &&
         Style.AllowShortBlocksOnASingleLine == FormatStyle::SBS_Never)
       return 0;
@@ -523,8 +540,9 @@ private:
         return 0;
       if (!Style.AllowShortIfStatementsOnASingleLine &&
           Line.startsWith(tok::kw_if) &&
-          Style.BraceWrapping.AfterControlStatement && I + 2 != E &&
-          !I[2]->First->is(tok::r_brace))
+          Style.BraceWrapping.AfterControlStatement ==
+              FormatStyle::BWACS_Always &&
+          I + 2 != E && !I[2]->First->is(tok::r_brace))
         return 0;
       if (!Style.AllowShortLoopsOnASingleLine &&
           Line.First->isOneOf(tok::kw_while, tok::kw_do, tok::kw_for) &&
@@ -533,8 +551,9 @@ private:
         return 0;
       if (!Style.AllowShortLoopsOnASingleLine &&
           Line.First->isOneOf(tok::kw_while, tok::kw_do, tok::kw_for) &&
-          Style.BraceWrapping.AfterControlStatement && I + 2 != E &&
-          !I[2]->First->is(tok::r_brace))
+          Style.BraceWrapping.AfterControlStatement ==
+              FormatStyle::BWACS_Always &&
+          I + 2 != E && !I[2]->First->is(tok::r_brace))
         return 0;
       // FIXME: Consider an option to allow short exception handling clauses on
       // a single line.
@@ -597,6 +616,17 @@ private:
         if (Tok->Next && Tok->Next->is(tok::kw_else))
           return 0;
 
+        // Don't merge a trailing multi-line control statement block like:
+        // } else if (foo &&
+        //            bar)
+        // { <-- current Line
+        //   baz();
+        // }
+        if (Line.First == Line.Last &&
+            Style.BraceWrapping.AfterControlStatement ==
+                FormatStyle::BWACS_MultiLine)
+          return 0;
+
         return 2;
       }
     } else if (I[1]->First->is(tok::l_brace)) {
diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 8fd0e9433b6..bbe05602f6d 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1167,7 +1167,8 @@ void UnwrappedLineParser::parseStructuralElement() {
       case tok::objc_autoreleasepool:
         nextToken();
         if (FormatTok->Tok.is(tok::l_brace)) {
-          if (Style.BraceWrapping.AfterControlStatement)
+          if (Style.BraceWrapping.AfterControlStatement ==
+              FormatStyle::BWACS_Always)
             addUnwrappedLine();
           parseBlock(/*MustBeDeclaration=*/false);
         }
@@ -1179,7 +1180,8 @@ void UnwrappedLineParser::parseStructuralElement() {
           // Skip synchronization object
           parseParens();
         if (FormatTok->Tok.is(tok::l_brace)) {
-          if (Style.BraceWrapping.AfterControlStatement)
+          if (Style.BraceWrapping.AfterControlStatement ==
+              FormatStyle::BWACS_Always)
             addUnwrappedLine();
           parseBlock(/*MustBeDeclaration=*/false);
         }
@@ -1989,7 +1991,8 @@ void UnwrappedLineParser::parseLabel(bool LeftAlignLabel) {
                                        Style.BraceWrapping.IndentBraces);
     parseBlock(/*MustBeDeclaration=*/false);
     if (FormatTok->Tok.is(tok::kw_break)) {
-      if (Style.BraceWrapping.AfterControlStatement)
+      if (Style.BraceWrapping.AfterControlStatement ==
+          FormatStyle::BWACS_Always)
         addUnwrappedLine();
       parseStructuralElement();
     }