Allow error test expectations to omit the implicit line.

Error tests with explicit line/column markers, like
 [error line 123, column 456]
currently require both "line" and "column".
All existing occurrences of `[error line 123, column 456]` always
refer to the most recent non-comment line *just like* the `// ^^` lines,
so omitting the line, and having the most recent non-comment line
as the *default* line, seems reasonable.

This CL makes the line optional, the new format without a "line" entry
will be just `[error column 456]`.

This allows files to change the number of lines in the code without
invalidating any later expectations.
(Or, say, remove a comment line at the top of the file!)

Omits the line entry by default when writing/updating expectations.

Change-Id: Ia0c95bf804a1c6b11c0c1621bfd481e43f8fa0c0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/200429
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

pkg/test_runner/lib/src/static_error.dart

@@ -455,15 +455,23 @@ class _ErrorExpectationParser {
   /// Matches an explicit error location with a length, like:
   ///
   ///     // [error line 1, column 17, length 3]
-  static final _explicitLocationAndLengthRegExp =
-      RegExp(r"^\s*//\s*\[\s*error line\s+(\d+)\s*,\s*column\s+(\d+)\s*,\s*"
-          r"length\s+(\d+)\s*\]\s*$");
+  ///
+  /// or implicitly on the previous line
+  ///
+  ///     // [error column 17, length 3]
+  static final _explicitLocationAndLengthRegExp = RegExp(
+      r"^\s*//\s*\[\s*error (?:line\s+(\d+)\s*,)?\s*column\s+(\d+)\s*,\s*"
+      r"length\s+(\d+)\s*\]\s*$");
 
   /// Matches an explicit error location without a length, like:
   ///
   ///     // [error line 1, column 17]
-  static final _explicitLocationRegExp =
-      RegExp(r"^\s*//\s*\[\s*error line\s+(\d+)\s*,\s*column\s+(\d+)\s*\]\s*$");
+  ///
+  /// or implicitly on the previous line.
+  ///
+  ///     // [error column 17]
+  static final _explicitLocationRegExp = RegExp(
+      r"^\s*//\s*\[\s*error (?:line\s+(\d+)\s*,)?\s*column\s+(\d+)\s*\]\s*$");
 
   /// Matches the beginning of an error message, like `// [analyzer]`.
   ///
@@ -518,25 +526,28 @@ class _ErrorExpectationParser {
         _parseErrors(
             line: _lastRealLine,
             column: sourceLine.indexOf("^") + 1,
-            length: match.group(1).length);
+            length: match[1].length);
         _advance();
         continue;
       }
 
       match = _explicitLocationAndLengthRegExp.firstMatch(sourceLine);
       if (match != null) {
+        var lineCapture = match[1];
         _parseErrors(
-            line: int.parse(match.group(1)),
-            column: int.parse(match.group(2)),
-            length: int.parse(match.group(3)));
+            line: lineCapture == null ? _lastRealLine : int.parse(lineCapture),
+            column: int.parse(match[2]),
+            length: int.parse(match[3]));
         _advance();
         continue;
       }
 
       match = _explicitLocationRegExp.firstMatch(sourceLine);
       if (match != null) {
+        var lineCapture = match[1];
         _parseErrors(
-            line: int.parse(match.group(1)), column: int.parse(match.group(2)));
+            line: lineCapture == null ? _lastRealLine : int.parse(lineCapture),
+            column: int.parse(match[2]));
         _advance();
         continue;
       }
@@ -559,16 +570,16 @@ class _ErrorExpectationParser {
       var match = _errorMessageRegExp.firstMatch(_peek(1));
       if (match == null) break;
 
-      var number = match.group(2) != null ? int.parse(match.group(2)) : null;
+      var number = match[2] != null ? int.parse(match[2]) : null;
 
-      var sourceName = match.group(1);
+      var sourceName = match[1];
       var source = ErrorSource.find(sourceName);
       if (source == null) _fail("Unknown front end '[$sourceName]'.");
       if (source == ErrorSource.context && number == null) {
         _fail("Context messages must have an error number.");
       }
 
-      var message = match.group(3);
+      var message = match[3];
       _advance();
       var sourceLines = {locationLine, _currentLine};
 
@@ -587,7 +598,7 @@ class _ErrorExpectationParser {
         var messageMatch = _errorMessageRestRegExp.firstMatch(nextLine);
         if (messageMatch == null) break;
 
-        message += "\n" + messageMatch.group(1);
+        message += "\n" + messageMatch[1];
         _advance();
         sourceLines.add(_currentLine);
       }

pkg/test_runner/lib/src/update_errors.dart

@@ -85,19 +85,12 @@ String updateErrorExpectations(String source, List<StaticError> errors,
 
   // Rebuild the source file a line at a time.
   var previousIndent = 0;
-  var codeLine = 1;
   var result = <String>[];
   for (var i = 0; i < lines.length; i++) {
     // Keep the code.
     if (lines[i] != null) {
       result.add(lines[i]);
       previousIndent = _countIndentation(lines[i]);
-
-      // Keep track of the resulting line number of the last line containing
-      // real code. We use this when outputting explicit line numbers instead
-      // the error's reported line to compensate for added or removed lines
-      // above the error.
-      codeLine = result.length;
     }
 
     // Add expectations for any errors reported on this line.
@@ -124,13 +117,13 @@ String updateErrorExpectations(String source, List<StaticError> errors,
               error.length != null &&
               error.length != previousLength)) {
         // If the error can't fit in a line comment, or no source location is
-        // sepcified, use an explicit location.
+        // specified, use an explicit location.
         if (error.column <= 2 || error.length == 0) {
           if (error.length == null) {
-            result.add("$comment [error line $codeLine, column "
+            result.add("$comment [error column "
                 "${error.column}]");
           } else {
-            result.add("$comment [error line $codeLine, column "
+            result.add("$comment [error column "
                 "${error.column}, length ${error.length}]");
           }
         } else {

pkg/test_runner/test/update_errors_test.dart

@@ -268,12 +268,12 @@ int j =
   ], expected: """
 int i =
 "bad";
-/\/ [error line 2, column 1, length 5]
+/\/ [error column 1, length 5]
 /\/ [analyzer] updated.error
 
 int j =
 "bad";
-/\/ [error line 7, column 1, length 5]
+/\/ [error column 1, length 5]
 /\/ [cfe] Error.
 """);
 
@@ -293,7 +293,7 @@ int i =
 """, errors: [makeError(line: 2, column: 1, cfeError: "Error.")], expected: """
 int i =
 "bad";
-/\/ [error line 2, column 1]
+/\/ [error column 1]
 /\/ [cfe] Error.
 """);
 
@@ -314,9 +314,9 @@ Error here;
 main() {
 }
 Error here;
-/\/ [error line 3, column 1, length 5]
+/\/ [error column 1, length 5]
 /\/ [analyzer] NEW.ERROR
-/\/ [error line 3, column 2, length 3]
+/\/ [error column 2, length 3]
 /\/ [cfe] Error.
 """);
 
@@ -400,7 +400,7 @@ x
     makeError(line: 1, column: 1, length: 0, cfeError: "Foo"),
   ], expected: """
 x
-// [error line 1, column 1, length 0]
+// [error column 1, length 0]
 // [cfe] Foo""");
 
   contextMessages();