[Parse][SR-1545] Lexing of source control conflict markers

include/swift/AST/DiagnosticsParse.def

@@ -141,7 +141,8 @@ ERROR(lex_editor_placeholder,none,
       "editor placeholder in source file", ())
 WARNING(lex_editor_placeholder_in_playground,none,
         "editor placeholder in source file", ())
-
+ERROR(lex_conflict_marker_in_file,none,
+      "source control conflict marker in source file", ())
 //------------------------------------------------------------------------------
 // Declaration parsing diagnostics
 //------------------------------------------------------------------------------

include/swift/Parse/Lexer.h

@@ -36,6 +36,16 @@ enum class CommentRetentionMode {
   ReturnAsTokens,
 };
 
+/// Kinds of conflict marker which the lexer might encounter.
+enum class ConflictMarkerKind {
+  /// A normal or diff3 conflict marker, initiated by at least 7 "<"s,
+  /// separated by at least 7 "="s or "|"s, and terminated by at least 7 ">"s.
+  Normal,
+  /// A Perforce-style conflict marker, initiated by 4 ">"s,
+  /// separated by 4 "="s, and terminated by 4 "<"s.
+  Perforce
+};
+
 class Lexer {
   const LangOptions &LangOpts;
   const SourceManager &SourceMgr;
@@ -438,6 +448,10 @@ class Lexer {
 
   void tryLexEditorPlaceholder();
   const char *findEndOfCurlyQuoteStringLiteral(const char*);
+
+  /// Try to lex conflict markers by checking for the presence of the start and
+  /// end of the marker in diff3 or Perforce style respectively.
+  bool tryLexConflictMarker();
 };
 
 } // end namespace swift

lib/Parse/Lexer.cpp

@@ -1373,6 +1373,61 @@ void Lexer::lexEscapedIdentifier() {
   formToken(tok::backtick, Quote);
 }
 
+/// Find the end of a version control conflict marker.
+static const char *findConflictEnd(const char *CurPtr, const char *BufferEnd,
+                                   ConflictMarkerKind CMK) {
+  StringRef terminator = CMK == ConflictMarkerKind::Perforce ? "<<<<\n"
+                                                             : ">>>>>>> ";
+  size_t termLen = terminator.size();
+
+  // Get a reference to the rest of the buffer minus the length of the start
+  // of the conflict marker.
+  auto restOfBuffer = StringRef(CurPtr, BufferEnd - CurPtr).substr(termLen);
+  size_t endPos = restOfBuffer.find(terminator);
+  while (endPos != StringRef::npos) {
+    // Must occur at start of line.
+    if (endPos != 0 &&
+        (restOfBuffer[endPos - 1] == '\r' || restOfBuffer[endPos - 1] == '\n'))
+    {
+      return restOfBuffer.data() + endPos;
+    }
+    restOfBuffer = restOfBuffer.substr(endPos + termLen);
+    endPos = restOfBuffer.find(terminator);
+  }
+  return nullptr;
+}
+
+bool Lexer::tryLexConflictMarker() {
+  const char *Ptr = CurPtr - 1;
+
+  // Only a conflict marker if it starts at the beginning of a line.
+  if (Ptr != BufferStart && Ptr[-1] != '\n' && Ptr[-1] != '\r')
+    return false;
+
+  // Check to see if we have <<<<<<< or >>>>.
+  StringRef restOfBuffer(Ptr, BufferEnd - Ptr);
+  if (!restOfBuffer.startswith("<<<<<<< ") && !restOfBuffer.startswith(">>>> "))
+    return false;
+
+  ConflictMarkerKind Kind = *Ptr == '<' ? ConflictMarkerKind::Normal
+                                        : ConflictMarkerKind::Perforce;
+  if (const char *End = findConflictEnd(Ptr, BufferEnd, Kind)) {
+    // Diagnose at the conflict marker, then jump ahead to the end.
+    diagnose(CurPtr, diag::lex_conflict_marker_in_file);
+    CurPtr = End;
+
+    // Skip ahead to the end of the marker.
+    if (CurPtr != BufferEnd)
+      skipToEndOfLine();
+
+    return true;
+  }
+
+  // No end of conflict marker found.
+  return false;
+}
+
+
 void Lexer::tryLexEditorPlaceholder() {
   assert(CurPtr[-1] == '<' && CurPtr[0] == '#');
   const char *TokStart = CurPtr-1;
@@ -1689,10 +1744,17 @@ void Lexer::lexImpl() {
   case '<':
     if (CurPtr[0] == '#')
       return tryLexEditorPlaceholder();
-    SWIFT_FALLTHROUGH;
+    else if (CurPtr[0] == '<' && tryLexConflictMarker())
+      goto Restart;
+    return lexOperatorIdentifier();
 
-  case '=': case '-': case '+': case '*': case '>':
-  case '&': case '|': case '^': case '~': case '.':
+  case '>':
+    if (CurPtr[0] == '>' && tryLexConflictMarker())
+      goto Restart;
+    return lexOperatorIdentifier();
+
+  case '=': case '-': case '+': case '*':
+  case '&': case '|':  case '^': case '~': case '.':
     return lexOperatorIdentifier();
 
   case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case 'G':

test/Parse/conflict_markers.swift

@@ -0,0 +1,88 @@
+// RUN: %target-parse-verify-swift
+
+// Conflict marker parsing should never conflict with operator parsing.
+
+prefix operator <<<<<<< {}
+infix operator <<<<<<< {}
+
+prefix func <<<<<<< (x : String) {}
+func <<<<<<< (x : String, y : String) {}
+
+prefix operator >>>>>>> {}
+infix operator >>>>>>> {}
+
+prefix func >>>>>>> (x : String) {}
+func >>>>>>> (x : String, y : String) {}
+
+// diff3-style conflict markers
+
+<<<<<<< HEAD:conflict_markers.swift // expected-error {{source control conflict marker in source file}}
+var a : String = "A"
+var b : String = "b"
+=======
+var a : String = "a"
+var b : String = "B"
+>>>>>>> 18844bc65229786b96b89a9fc7739c0fc897905e:conflict_markers.swift
+print(a + b) // expected-error {{use of unresolved identifier 'a'}} expected-error {{use of unresolved identifier 'b'}}
+
+<<<<<<< HEAD:conflict_markers.swift // expected-error {{source control conflict marker in source file}}
+======= 
+var d : String = "D"
+>>>>>>> 18844bc65229786b96b89a9fc7739c0fc897905e:conflict_markers.swift
+print(d) // expected-error {{use of unresolved identifier 'd'}}
+
+<<<<<<<"HEAD:fake_conflict_markers.swift" // No error
+>>>>>>>"18844bc65229786b96b89a9fc7739c0fc897905e:fake_conflict_markers.swift" // No error
+
+<<<<<<< HEAD:conflict_markers.swift // expected-error {{source control conflict marker in source file}}
+<<<<<<<"HEAD:fake_conflict_markers.swift"
+var fake_b : String = "a"
+>>>>>>>"18844bc65229786b96b89a9fc7739c0fc897905e:fake_conflict_markers.swift"
+=======
+<<<<<<<"HEAD:fake_conflict_markers.swift"
+var fake_c : String = "a"
+>>>>>>>"18844bc65229786b96b89a9fc7739c0fc897905e:fake_conflict_markers.swift"
+>>>>>>> 18844bc65229786b96b89a9fc7739c0fc897905e:conflict_markers.swift
+print(fake_b + fake_c) // expected-error {{use of unresolved identifier 'fake_b'}} expected-error {{use of unresolved identifier 'fake_c'}}
+
+// Disambiguating conflict markers from operator applications.
+
+_ = {
+
+// Conflict marker.
+
+let a = "a", b = "b"
+a // expected-warning {{expression of type 'String' is unused}}
+<<<<<<< b // expected-error {{source control conflict marker in source file}}
+a
+>>>>>>> b
+
+// Not a conflict marker.
+
+a
+  <<<<<<< b
+a
+  >>>>>>> b
+}()
+
+// Perforce-style conflict markers
+
+>>>> ORIGINAL // expected-error {{source control conflict marker in source file}}
+var a : String = "A"
+var b : String = "B"
+==== THEIRS
+var a : String = "A"
+var b : String = "b"
+==== YOURS
+var a : String = "a"
+var b : String = "B"
+<<<<
+print(a + b) // expected-error {{use of unresolved identifier 'a'}} expected-error {{use of unresolved identifier 'b'}}
+
+>>>> ORIGINAL // expected-error {{source control conflict marker in source file}}
+==== THEIRS
+==== YOURS
+var d : String = "D"
+<<<<
+print(d) // expected-error {{use of unresolved identifier 'd'}}
+