go/parser: report illegal label declarations at ':' rather than guessing the start

Also:
- Add parser.SpuriousError flag. If set, the parser reports all (including
  spurious) errors rather then at most one error per line.
- Add -e flag to gofmt and gotype: If set, gofmt and gotype report all
  (including spurious) errors rather than at most one error per line.
- Updated the respective documentation.

Fixes #2088.

R=rsc
CC=golang-dev
https://golang.org/cl/4803047

src/cmd/gofmt/doc.go

@@ -14,11 +14,12 @@ Usage:
 	gofmt [flags] [path ...]
 
 The flags are:
-
 	-d
 		Do not print reformatted sources to standard output.
 		If a file's formatting is different than gofmt's, print diffs
 		to standard output.
+	-e
+		Print all (including spurious) errors.
 	-l
 		Do not print reformatted sources to standard output.
 		If a file's formatting is different from gofmt's, print its name
@@ -31,6 +32,8 @@ The flags are:
 		Do not print reformatted sources to standard output.
 		If a file's formatting is different from gofmt's, overwrite it
 		with gofmt's version.
+
+Formatting control flags:
 	-comments=true
 		Print comments; if false, all comments are elided from the output.
 	-spaces
@@ -40,6 +43,7 @@ The flags are:
 	-tabwidth=8
 		Tab width in spaces.
 
+
 The rewrite rule specified with the -r flag must be a string of the form:
 
 	pattern -> replacement

src/cmd/gofmt/gofmt.go

@@ -29,6 +29,7 @@ var (
 	rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'α[β:len(α)] -> α[β:]')")
 	simplifyAST = flag.Bool("s", false, "simplify code")
 	doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
+	allErrors   = flag.Bool("e", false, "print all (including spurious) errors")
 
 	// layout control
 	comments  = flag.Bool("comments", true, "print comments")
@@ -64,6 +65,9 @@ func initParserMode() {
 	if *comments {
 		parserMode |= parser.ParseComments
 	}
+	if *allErrors {
+		parserMode |= parser.SpuriousErrors
+	}
 }
 
 func initPrinterMode() {

src/cmd/gotype/doc.go

@@ -24,18 +24,20 @@ Usage:
 	gotype [flags] [path ...]
 
 The flags are:
+	-e
+		Print all (including spurious) errors.
 	-p pkgName
-		process only those files in package pkgName.
+		Process only those files in package pkgName.
 	-r
-		recursively process subdirectories.
+		Recursively process subdirectories.
 	-v
-		verbose mode.
+		Verbose mode.
 
 Debugging flags:
-	-trace
-		print parse trace (disables concurrent parsing).
 	-ast
-		print AST (disables concurrent parsing).
+		Print AST (disables concurrent parsing).
+	-trace
+		Print parse trace (disables concurrent parsing).
 
 
 Examples

src/cmd/gotype/gotype.go

@@ -23,6 +23,7 @@ var (
 	pkgName   = flag.String("p", "", "process only those files in package pkgName")
 	recursive = flag.Bool("r", false, "recursively process subdirectories")
 	verbose   = flag.Bool("v", false, "verbose mode")
+	allErrors = flag.Bool("e", false, "print all (including spurious) errors")
 
 	// debugging support
 	printTrace = flag.Bool("trace", false, "print parse trace")
@@ -68,6 +69,9 @@ func parse(fset *token.FileSet, filename string, src []byte) *ast.File {
 
 	// parse entire file
 	mode := parser.DeclarationErrors
+	if *allErrors {
+		mode |= parser.SpuriousErrors
+	}
 	if *printTrace {
 		mode |= parser.Trace
 	}

src/pkg/go/parser/interface.go

@@ -48,9 +48,12 @@ func readSource(filename string, src interface{}) ([]byte, os.Error) {
 	return ioutil.ReadFile(filename)
 }
 
-func (p *parser) parseEOF() os.Error {
-	p.expect(token.EOF)
-	return p.GetError(scanner.Sorted)
+func (p *parser) errors() os.Error {
+	mode := scanner.Sorted
+	if p.mode&SpuriousErrors == 0 {
+		mode = scanner.NoMultiples
+	}
+	return p.GetError(mode)
 }
 
 // ParseExpr parses a Go expression and returns the corresponding
@@ -70,7 +73,9 @@ func ParseExpr(fset *token.FileSet, filename string, src interface{}) (ast.Expr,
 	if p.tok == token.SEMICOLON {
 		p.next() // consume automatically inserted semicolon, if any
 	}
-	return x, p.parseEOF()
+	p.expect(token.EOF)
+
+	return x, p.errors()
 }
 
 // ParseStmtList parses a list of Go statements and returns the list
@@ -86,7 +91,10 @@ func ParseStmtList(fset *token.FileSet, filename string, src interface{}) ([]ast
 
 	var p parser
 	p.init(fset, filename, data, 0)
-	return p.parseStmtList(), p.parseEOF()
+	list := p.parseStmtList()
+	p.expect(token.EOF)
+
+	return list, p.errors()
 }
 
 // ParseDeclList parses a list of Go declarations and returns the list
@@ -102,7 +110,10 @@ func ParseDeclList(fset *token.FileSet, filename string, src interface{}) ([]ast
 
 	var p parser
 	p.init(fset, filename, data, 0)
-	return p.parseDeclList(), p.parseEOF()
+	list := p.parseDeclList()
+	p.expect(token.EOF)
+
+	return list, p.errors()
 }
 
 // ParseFile parses the source code of a single Go source file and returns
@@ -133,7 +144,9 @@ func ParseFile(fset *token.FileSet, filename string, src interface{}, mode uint)
 
 	var p parser
 	p.init(fset, filename, data, mode)
-	return p.parseFile(), p.GetError(scanner.NoMultiples) // parseFile() reads to EOF
+	file := p.parseFile() // parseFile reads to EOF
+
+	return file, p.errors()
 }
 
 // ParseFiles calls ParseFile for each file in the filenames list and returns

src/pkg/go/parser/parser.go

@@ -26,6 +26,7 @@ const (
 	ParseComments                      // parse comments and add them to AST
 	Trace                              // print a trace of parsed productions
 	DeclarationErrors                  // report declaration errors
+	SpuriousErrors                     // report all (not just the first) errors per line
 )
 
 // The parser structure holds the parser's internal state.
@@ -1408,7 +1409,13 @@ func (p *parser) parseSimpleStmt(labelOk bool) ast.Stmt {
 			p.declare(stmt, nil, p.labelScope, ast.Lbl, label)
 			return stmt
 		}
-		p.error(x[0].Pos(), "illegal label declaration")
+		// The label declaration typically starts at x[0].Pos(), but the label
+		// declaration may be erroneous due to a token after that position (and
+		// before the ':'). If SpuriousErrors is not set, the (only) error re-
+		// ported for the line is the illegal label error instead of the token
+		// before the ':' that caused the problem. Thus, use the (latest) colon
+		// position for error reporting.
+		p.error(colon, "illegal label declaration")
 		return &ast.BadStmt{x[0].Pos(), colon + 1}
 
 	case token.ARROW: