go/parser: better error messages for missing commas

Fixes #3008.

R=rsc
CC=golang-dev
https://golang.org/cl/5660046

diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index e6dffa3709961df23f0c939e3ace797c7e7f7a31..6a0b61eb48cf3630396888b753d141a75561e4fa 100644 (file)
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -335,7 +335,7 @@ func (p *parser) errorExpected(pos token.Pos, msg string) {
        if pos == p.pos {
                // the error happened at the current position;
                // make the error message more specific
-               if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
+               if p.tok == token.SEMICOLON && p.lit == "\n" {
                        msg += ", found newline"
                } else {
                        msg += ", found '" + p.tok.String() + "'"
@@ -356,6 +356,17 @@ func (p *parser) expect(tok token.Token) token.Pos {
        return pos
 }
 
+// expectClosing is like expect but provides a better error message
+// for the common case of a missing comma before a newline.
+//
+func (p *parser) expectClosing(tok token.Token, construct string) token.Pos {
+       if p.tok != tok && p.tok == token.SEMICOLON && p.lit == "\n" {
+               p.error(p.pos, "missing ',' before newline in "+construct)
+               p.next()
+       }
+       return p.expect(tok)
+}
+
 func (p *parser) expectSemi() {
        if p.tok != token.RPAREN && p.tok != token.RBRACE {
                p.expect(token.SEMICOLON)
@@ -1056,7 +1067,7 @@ func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
                p.next()
        }
        p.exprLev--
-       rparen := p.expect(token.RPAREN)
+       rparen := p.expectClosing(token.RPAREN, "argument list")
 
        return &ast.CallExpr{fun, lparen, list, ellipsis, rparen}
 }
@@ -1111,7 +1122,7 @@ func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
                elts = p.parseElementList()
        }
        p.exprLev--
-       rbrace := p.expect(token.RBRACE)
+       rbrace := p.expectClosing(token.RBRACE, "composite literal")
        return &ast.CompositeLit{typ, lbrace, elts, rbrace}
 }