cmd/compile/internal/syntax: match old parser errors and line numbers

This makes a bunch of changes to package syntax to tweak line numbers
for AST nodes. For example, short variable declaration statements are
now associated with the location of the ":=" token, and function calls
are associated with the location of the final ")" token. These help
satisfy many unit tests that assume the old parser's behavior.

Because many of these changes are questionable, they're guarded behind
a new "gcCompat" const to make them easy to identify and revisit in
the future.

A handful of remaining tests are too difficult to make behave
identically. These have been updated to execute with -newparser=0 and
comments explaining why they need to be fixed.

all.bash now passes with both the old and new parsers.

Change-Id: Iab834b71ca8698d39269f261eb5c92a0d55a3bf4
Reviewed-on: https://go-review.googlesource.com/27199
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

3 files changed, 146 insertions, 80 deletions

diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 40253224f0..9544001a2e 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -13,6 +13,11 @@ import (
 const debug = false
 const trace = false
 
+// The old gc parser assigned line numbers very inconsistently depending
+// on when it happened to construct AST nodes. To make transitioning to the
+// new AST easier, we try to mimick the behavior as much as possible.
+const gcCompat = true
+
 type parser struct {
 	scanner
 
@@ -60,6 +65,11 @@ func (p *parser) want(tok token) {
 
 // syntax_error reports a syntax error at the current line.
 func (p *parser) syntax_error(msg string) {
+	p.syntax_error_at(p.pos, p.line, msg)
+}
+
+// Like syntax_error, but reports error at given line rather than current lexer line.
+func (p *parser) syntax_error_at(pos, line int, msg string) {
 	if trace {
 		defer p.trace("syntax_error (" + msg + ")")()
 	}
@@ -78,15 +88,17 @@ func (p *parser) syntax_error(msg string) {
 		msg = ", " + msg
 	default:
 		// plain error - we don't care about current token
-		p.error("syntax error: " + msg)
+		p.error_at(pos, line, "syntax error: "+msg)
 		return
 	}
 
 	// determine token string
 	var tok string
 	switch p.tok {
-	case _Name, _Literal:
+	case _Name:
 		tok = p.lit
+	case _Literal:
+		tok = "literal " + p.lit
 	case _Operator:
 		tok = p.op.String()
 	case _AssignOp:
@@ -98,17 +110,7 @@ func (p *parser) syntax_error(msg string) {
 		tok = tokstring(p.tok)
 	}
 
-	p.error("syntax error: unexpected " + tok + msg)
-}
-
-// Like syntax_error, but reports error at given line rather than current lexer line.
-func (p *parser) syntax_error_at(lineno uint32, msg string) {
-	// TODO(gri) fix this
-	// defer func(lineno int32) {
-	// 	lexlineno = lineno
-	// }(lexlineno)
-	// lexlineno = lineno
-	p.syntax_error(msg)
+	p.error_at(pos, line, "syntax error: unexpected "+tok+msg)
 }
 
 // The stopset contains keywords that start a statement.
@@ -195,7 +197,10 @@ func (p *parser) file() *File {
 	f.init(p)
 
 	// PackageClause
-	p.want(_Package)
+	if !p.got(_Package) {
+		p.syntax_error("package statement must be first")
+		return nil
+	}
 	f.PkgName = p.name()
 	p.want(_Semi)
 
@@ -296,7 +301,7 @@ func (p *parser) importDecl(group *Group) Decl {
 		d.LocalPkgName = n
 		p.next()
 	}
-	if p.tok == _Literal && p.kind == StringLit {
+	if p.tok == _Literal && (gcCompat || p.kind == StringLit) {
 		d.Path = p.oliteral()
 	} else {
 		p.syntax_error("missing import path; require quoted string")
@@ -384,17 +389,18 @@ func (p *parser) funcDecl() *FuncDecl {
 	f := new(FuncDecl)
 	f.init(p)
 
+	badRecv := false
 	if p.tok == _Lparen {
 		rcvr := p.paramList()
 		switch len(rcvr) {
 		case 0:
 			p.error("method has no receiver")
-			return nil // TODO(gri) better solution
+			badRecv = true
 		case 1:
 			f.Recv = rcvr[0]
 		default:
 			p.error("method has multiple receivers")
-			return nil // TODO(gri) better solution
+			badRecv = true
 		}
 	}
 
@@ -429,6 +435,9 @@ func (p *parser) funcDecl() *FuncDecl {
 	// 	p.error("can only use //go:noescape with external func implementations")
 	// }
 
+	if badRecv {
+		return nil // TODO(gri) better solution
+	}
 	return f
 }
 
@@ -510,25 +519,29 @@ func (p *parser) unaryExpr() Expr {
 		//   <-(chan E)   =>  (<-chan E)
 		//   <-(chan<-E)  =>  (<-chan (<-E))
 
-		if x, ok := x.(*ChanType); ok {
+		if _, ok := x.(*ChanType); ok {
 			// x is a channel type => re-associate <-
 			dir := SendOnly
 			t := x
-			for ok && dir == SendOnly {
-				dir = t.Dir
+			for dir == SendOnly {
+				c, ok := t.(*ChanType)
+				if !ok {
+					break
+				}
+				dir = c.Dir
 				if dir == RecvOnly {
 					// t is type <-chan E but <-<-chan E is not permitted
 					// (report same error as for "type _ <-<-chan E")
 					p.syntax_error("unexpected <-, expecting chan")
 					// already progressed, no need to advance
 				}
-				t.Dir = RecvOnly
-				t, ok = t.Elem.(*ChanType)
+				c.Dir = RecvOnly
+				t = c.Elem
 			}
 			if dir == SendOnly {
 				// channel dir is <- but channel element E is not a channel
 				// (report same error as for "type _ <-chan<-E")
-				p.syntax_error(fmt.Sprintf("unexpected %v, expecting chan", t))
+				p.syntax_error(fmt.Sprintf("unexpected %s, expecting chan", String(t)))
 				// already progressed, no need to advance
 			}
 			return x
@@ -538,7 +551,10 @@ func (p *parser) unaryExpr() Expr {
 		return &Operation{Op: Recv, X: x}
 	}
 
-	return p.pexpr(false)
+	// TODO(mdempsky): We need parens here so we can report an
+	// error for "(x) := true". It should be possible to detect
+	// and reject that more efficiently though.
+	return p.pexpr(true)
 }
 
 // callStmt parses call-like statements that can be preceded by 'defer' and 'go'.
@@ -556,6 +572,9 @@ func (p *parser) callStmt() *CallStmt {
 	switch x := x.(type) {
 	case *CallExpr:
 		s.Call = x
+		if gcCompat {
+			s.node = x.node
+		}
 	case *ParenExpr:
 		p.error(fmt.Sprintf("expression in %s must not be parenthesized", s.Tok))
 		// already progressed, no need to advance
@@ -760,13 +779,7 @@ loop:
 			p.xnest--
 
 		case _Lparen:
-			// call or conversion
-			// convtype '(' expr ocomma ')'
-			c := new(CallExpr)
-			c.init(p)
-			c.Fun = x
-			c.ArgList, c.HasDots = p.argList()
-			x = c
+			x = p.call(x)
 
 		case _Lbrace:
 			// operand may have returned a parenthesized complit
@@ -1032,6 +1045,9 @@ func (p *parser) structType() *StructType {
 			break
 		}
 	}
+	if gcCompat {
+		typ.init(p)
+	}
 	p.want(_Rbrace)
 
 	return typ
@@ -1056,6 +1072,9 @@ func (p *parser) interfaceType() *InterfaceType {
 			break
 		}
 	}
+	if gcCompat {
+		typ.init(p)
+	}
 	p.want(_Rbrace)
 
 	return typ
@@ -1446,7 +1465,8 @@ func (p *parser) simpleStmt(lhs Expr, rangeOk bool) SimpleStmt {
 		return p.newAssignStmt(0, lhs, p.exprList())
 
 	case _Define:
-		//lno := lineno
+		var n node
+		n.init(p)
 		p.next()
 
 		if rangeOk && p.got(_Range) {
@@ -1470,7 +1490,11 @@ func (p *parser) simpleStmt(lhs Expr, rangeOk bool) SimpleStmt {
 			return &ExprStmt{X: x}
 		}
 
-		return p.newAssignStmt(Def, lhs, rhs)
+		as := p.newAssignStmt(Def, lhs, rhs)
+		if gcCompat {
+			as.node = n
+		}
+		return as
 
 	default:
 		p.syntax_error("expecting := or = or comma")
@@ -1502,21 +1526,22 @@ func (p *parser) labeledStmt(label *Name) Stmt {
 		defer p.trace("labeledStmt")()
 	}
 
-	var ls Stmt // labeled statement
+	s := new(LabeledStmt)
+	s.init(p)
+	s.Label = label
+
+	p.want(_Colon)
+
 	if p.tok != _Rbrace && p.tok != _EOF {
-		ls = p.stmt()
-		if ls == missing_stmt {
+		s.Stmt = p.stmt()
+		if s.Stmt == missing_stmt {
 			// report error at line of ':' token
-			p.syntax_error_at(label.line, "missing statement after label")
+			p.syntax_error_at(int(label.pos), int(label.line), "missing statement after label")
 			// we are already at the end of the labeled statement - no need to advance
 			return missing_stmt
 		}
 	}
 
-	s := new(LabeledStmt)
-	s.init(p)
-	s.Label = label
-	s.Stmt = ls
 	return s
 }
 
@@ -1590,8 +1615,8 @@ func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleSt
 
 	if p.tok != _Semi {
 		// accept potential varDecl but complain
-		if p.got(_Var) {
-			p.error("var declaration not allowed in initializer")
+		if forStmt && p.got(_Var) {
+			p.error("var declaration not allowed in for initializer")
 		}
 		init = p.simpleStmt(nil, forStmt)
 		// If we have a range clause, we are done.
@@ -1650,10 +1675,14 @@ func (p *parser) ifStmt() *IfStmt {
 	s.Then = p.stmtBody("if clause")
 
 	if p.got(_Else) {
-		if p.tok == _If {
+		switch p.tok {
+		case _If:
 			s.Else = p.ifStmt()
-		} else {
+		case _Lbrace:
 			s.Else = p.blockStmt()
+		default:
+			p.error("else must be followed by if or statement block")
+			p.advance(_Name, _Rbrace)
 		}
 	}
 
@@ -1725,6 +1754,9 @@ func (p *parser) caseClause() *CaseClause {
 		p.advance(_Case, _Default, _Rbrace)
 	}
 
+	if gcCompat {
+		c.init(p)
+	}
 	p.want(_Colon)
 	c.Body = p.stmtList()
 
@@ -1769,6 +1801,9 @@ func (p *parser) commClause() *CommClause {
 		p.advance(_Case, _Default, _Rbrace)
 	}
 
+	if gcCompat {
+		c.init(p)
+	}
 	p.want(_Colon)
 	c.Body = p.stmtList()
 
@@ -1794,7 +1829,7 @@ func (p *parser) stmt() Stmt {
 	// look for it first before doing anything more expensive.
 	if p.tok == _Name {
 		lhs := p.exprList()
-		if label, ok := lhs.(*Name); ok && p.got(_Colon) {
+		if label, ok := lhs.(*Name); ok && p.tok == _Colon {
 			return p.labeledStmt(label)
 		}
 		return p.simpleStmt(lhs, false)
@@ -1916,26 +1951,35 @@ func (p *parser) stmtList() (l []Stmt) {
 }
 
 // Arguments = "(" [ ( ExpressionList | Type [ "," ExpressionList ] ) [ "..." ] [ "," ] ] ")" .
-func (p *parser) argList() (list []Expr, hasDots bool) {
+func (p *parser) call(fun Expr) *CallExpr {
 	if trace {
-		defer p.trace("argList")()
+		defer p.trace("call")()
 	}
 
+	// call or conversion
+	// convtype '(' expr ocomma ')'
+	c := new(CallExpr)
+	c.init(p)
+	c.Fun = fun
+
 	p.want(_Lparen)
 	p.xnest++
 
 	for p.tok != _EOF && p.tok != _Rparen {
-		list = append(list, p.expr()) // expr_or_type
-		hasDots = p.got(_DotDotDot)
-		if !p.ocomma(_Rparen) || hasDots {
+		c.ArgList = append(c.ArgList, p.expr()) // expr_or_type
+		c.HasDots = p.got(_DotDotDot)
+		if !p.ocomma(_Rparen) || c.HasDots {
 			break
 		}
 	}
 
 	p.xnest--
+	if gcCompat {
+		c.init(p)
+	}
 	p.want(_Rparen)
 
-	return
+	return c
 }
 
 // ----------------------------------------------------------------------------
diff --git a/src/cmd/compile/internal/syntax/scanner.go b/src/cmd/compile/internal/syntax/scanner.go
index 0f0f1ead9a..d02bb6d11b 100644
--- a/src/cmd/compile/internal/syntax/scanner.go
+++ b/src/cmd/compile/internal/syntax/scanner.go
@@ -46,7 +46,7 @@ redo:
 	// token start
 	s.pos, s.line = s.source.pos0(), s.source.line0
 
-	if isLetter(c) || c >= utf8.RuneSelf && unicode.IsLetter(c) {
+	if isLetter(c) || c >= utf8.RuneSelf && (unicode.IsLetter(c) || s.isCompatRune(c, true)) {
 		s.ident()
 		return
 	}
@@ -271,7 +271,7 @@ redo:
 
 	default:
 		s.tok = 0
-		s.error(fmt.Sprintf("invalid rune %q", c))
+		s.error(fmt.Sprintf("illegal character %#U", c))
 		goto redo
 	}
 
@@ -305,7 +305,7 @@ func (s *scanner) ident() {
 
 	// general case
 	if c >= utf8.RuneSelf {
-		for unicode.IsLetter(c) || c == '_' || unicode.IsDigit(c) {
+		for unicode.IsLetter(c) || c == '_' || unicode.IsDigit(c) || s.isCompatRune(c, false) {
 			c = s.getr()
 		}
 	}
@@ -327,6 +327,18 @@ func (s *scanner) ident() {
 	s.tok = _Name
 }
 
+func (s *scanner) isCompatRune(c rune, start bool) bool {
+	if !gcCompat || c < utf8.RuneSelf {
+		return false
+	}
+	if start && unicode.IsNumber(c) {
+		s.error(fmt.Sprintf("identifier cannot begin with digit %#U", c))
+	} else {
+		s.error(fmt.Sprintf("invalid identifier character %#U", c))
+	}
+	return true
+}
+
 // hash is a perfect hash function for keywords.
 // It assumes that s has at least length 2.
 func hash(s []byte) uint {
@@ -496,24 +508,26 @@ func (s *scanner) rune() {
 	s.startLit()
 
 	r := s.getr()
+	ok := false
 	if r == '\'' {
-		s.error("empty character literal")
+		s.error("empty character literal or unescaped ' in character literal")
 	} else if r == '\n' {
 		s.ungetr() // assume newline is not part of literal
 		s.error("newline in character literal")
 	} else {
-		ok := true
+		ok = true
 		if r == '\\' {
 			ok = s.escape('\'')
 		}
-		r = s.getr()
-		if r != '\'' {
-			// only report error if we're ok so far
-			if ok {
-				s.error("missing '")
-			}
-			s.ungetr()
+	}
+
+	r = s.getr()
+	if r != '\'' {
+		// only report error if we're ok so far
+		if ok {
+			s.error("missing '")
 		}
+		s.ungetr()
 	}
 
 	s.nlsemi = true
@@ -623,10 +637,18 @@ func (s *scanner) escape(quote rune) bool {
 			if c < 0 {
 				return true // complain in caller about EOF
 			}
-			if c != quote {
-				s.error(fmt.Sprintf("illegal character %#U in escape sequence", c))
+			if gcCompat {
+				name := "hex"
+				if base == 8 {
+					name = "octal"
+				}
+				s.error(fmt.Sprintf("non-%s character in escape sequence: %c", name, c))
 			} else {
-				s.error("escape sequence incomplete")
+				if c != quote {
+					s.error(fmt.Sprintf("illegal character %#U in escape sequence", c))
+				} else {
+					s.error("escape sequence incomplete")
+				}
 			}
 			s.ungetr()
 			return false
@@ -637,7 +659,7 @@ func (s *scanner) escape(quote rune) bool {
 	}
 	s.ungetr()
 
-	if x > max && n == 3 {
+	if x > max && base == 8 {
 		s.error(fmt.Sprintf("octal escape value > 255: %d", x))
 		return false
 	}
diff --git a/src/cmd/compile/internal/syntax/scanner_test.go b/src/cmd/compile/internal/syntax/scanner_test.go
index 69e81aceca..4b582ccfdf 100644
--- a/src/cmd/compile/internal/syntax/scanner_test.go
+++ b/src/cmd/compile/internal/syntax/scanner_test.go
@@ -269,7 +269,7 @@ func TestScanErrors(t *testing.T) {
 
 		// token-level errors
 		{"x + ~y", "bitwise complement operator is ^", 4, 1},
-		{"foo$bar = 0", "invalid rune '$'", 3, 1},
+		{"foo$bar = 0", "illegal character U+0024 '$'", 3, 1},
 		{"const x = 0xyz", "malformed hex constant", 12, 1},
 		{"0123456789", "malformed octal constant", 10, 1},
 		{"0123456789. /* foobar", "comment not terminated", 12, 1},   // valid float constant
@@ -277,17 +277,17 @@ func TestScanErrors(t *testing.T) {
 		{"var a, b = 08, 07\n", "malformed octal constant", 13, 1},
 		{"(x + 1.0e+x)", "malformed floating-point constant exponent", 10, 1},
 
-		{`''`, "empty character literal", 1, 1},
+		{`''`, "empty character literal or unescaped ' in character literal", 1, 1},
 		{"'\n", "newline in character literal", 1, 1},
 		{`'\`, "missing '", 2, 1},
 		{`'\'`, "missing '", 3, 1},
 		{`'\x`, "missing '", 3, 1},
-		{`'\x'`, "escape sequence incomplete", 3, 1},
+		{`'\x'`, "non-hex character in escape sequence: '", 3, 1},
 		{`'\y'`, "unknown escape sequence", 2, 1},
-		{`'\x0'`, "escape sequence incomplete", 4, 1},
-		{`'\00'`, "escape sequence incomplete", 4, 1},
+		{`'\x0'`, "non-hex character in escape sequence: '", 4, 1},
+		{`'\00'`, "non-octal character in escape sequence: '", 4, 1},
 		{`'\377' /*`, "comment not terminated", 7, 1}, // valid octal escape
-		{`'\378`, "illegal character U+0038 '8' in escape sequence", 4, 1},
+		{`'\378`, "non-octal character in escape sequence: 8", 4, 1},
 		{`'\400'`, "octal escape value > 255: 256", 5, 1},
 		{`'xx`, "missing '", 2, 1},
 
@@ -302,19 +302,19 @@ func TestScanErrors(t *testing.T) {
 		{`"\`, "string not terminated", 0, 1},
 		{`"\"`, "string not terminated", 0, 1},
 		{`"\x`, "string not terminated", 0, 1},
-		{`"\x"`, "escape sequence incomplete", 3, 1},
+		{`"\x"`, "non-hex character in escape sequence: \"", 3, 1},
 		{`"\y"`, "unknown escape sequence", 2, 1},
-		{`"\x0"`, "escape sequence incomplete", 4, 1},
-		{`"\00"`, "escape sequence incomplete", 4, 1},
+		{`"\x0"`, "non-hex character in escape sequence: \"", 4, 1},
+		{`"\00"`, "non-octal character in escape sequence: \"", 4, 1},
 		{`"\377" /*`, "comment not terminated", 7, 1}, // valid octal escape
-		{`"\378"`, "illegal character U+0038 '8' in escape sequence", 4, 1},
+		{`"\378"`, "non-octal character in escape sequence: 8", 4, 1},
 		{`"\400"`, "octal escape value > 255: 256", 5, 1},
 
 		{`s := "foo\z"`, "unknown escape sequence", 10, 1},
 		{`s := "foo\z00\nbar"`, "unknown escape sequence", 10, 1},
 		{`"\x`, "string not terminated", 0, 1},
-		{`"\x"`, "escape sequence incomplete", 3, 1},
-		{`var s string = "\x"`, "escape sequence incomplete", 18, 1},
+		{`"\x"`, "non-hex character in escape sequence: \"", 3, 1},
+		{`var s string = "\x"`, "non-hex character in escape sequence: \"", 18, 1},
 		{`return "\Uffffffff"`, "escape sequence is invalid Unicode code point", 18, 1},
 
 		// former problem cases