[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

1 files changed, 37 insertions, 7 deletions

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)) {