[clang-format] Handle trailing comment sections in import statement lines

Summary:
This patch updates the handling of multiline trailing comment sections in
import statement lines to make it more consistent with the case in general.
This includes updating the parsing logic to collect the trailing comment
sections and the formatting logic to not insert escaped newlines at the end of
comment lines in import statement lines.

Specifically, before this patch this code:
```
#include <a> // line 1
             // line 2
```
will be turned into two unwrapped lines, whereas this code:
```
int i; // line 1
       // line 2
```
is turned into a single unwrapped line, enabling reflowing across comments.

An example where the old behaviour is bad is when partially formatting the lines
3 to 4 of this code:
```
#include <a> // line 1
             // line 2

int i;
```
which gets turned into:
```
#include <a> // line 1
             // line 2

             int i;
```
because the two comment lines were independent and the indent was copied.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D33351

llvm-svn: 303415

1 files changed, 14 insertions, 7 deletions

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 5758854e7c8..2bcb2d49652 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -55,13 +55,18 @@ private:
   std::vector<bool> &Stack;
 };
 
+static bool isLineComment(const FormatToken &FormatTok) {
+  return FormatTok.is(tok::comment) &&
+         FormatTok.TokenText.startswith("//");
+}
+
 class ScopedMacroState : public FormatTokenSource {
 public:
   ScopedMacroState(UnwrappedLine &Line, FormatTokenSource *&TokenSource,
                    FormatToken *&ResetToken)
       : Line(Line), TokenSource(TokenSource), ResetToken(ResetToken),
         PreviousLineLevel(Line.Level), PreviousTokenSource(TokenSource),
-        Token(nullptr) {
+        Token(nullptr), PreviousToken(nullptr) {
     TokenSource = this;
     Line.Level = 0;
     Line.InPPDirective = true;
@@ -78,6 +83,7 @@ public:
     // The \c UnwrappedLineParser guards against this by never calling
     // \c getNextToken() after it has encountered the first eof token.
     assert(!eof());
+    PreviousToken = Token;
     Token = PreviousTokenSource->getNextToken();
     if (eof())
       return getFakeEOF();
@@ -87,12 +93,17 @@ public:
   unsigned getPosition() override { return PreviousTokenSource->getPosition(); }
 
   FormatToken *setPosition(unsigned Position) override {
+    PreviousToken = nullptr;
     Token = PreviousTokenSource->setPosition(Position);
     return Token;
   }
 
 private:
-  bool eof() { return Token && Token->HasUnescapedNewline; }
+  bool eof() {
+    return Token && Token->HasUnescapedNewline &&
+           !(PreviousToken && isLineComment(*PreviousToken) &&
+             isLineComment(*Token) && Token->NewlinesBefore == 1);
+  }
 
   FormatToken *getFakeEOF() {
     static bool EOFInitialized = false;
@@ -112,6 +123,7 @@ private:
   FormatTokenSource *PreviousTokenSource;
 
   FormatToken *Token;
+  FormatToken *PreviousToken;
 };
 
 } // end anonymous namespace
@@ -2092,11 +2104,6 @@ bool UnwrappedLineParser::isOnNewLine(const FormatToken &FormatTok) {
          FormatTok.NewlinesBefore > 0;
 }
 
-static bool isLineComment(const FormatToken &FormatTok) {
-  return FormatTok.is(tok::comment) &&
-         FormatTok.TokenText.startswith("//");
-}
-
 // Checks if \p FormatTok is a line comment that continues the line comment
 // section on \p Line.
 static bool continuesLineComment(const FormatToken &FormatTok,