text/template: fix a couple of parse bugs around identifiers.

1) Poor error checking in variable declarations admitted
$x=2 or even $x%2.
2) Need white space or suitable termination character
after identifiers, so $x+2 doesn't parse, in case we want it
to mean something one day.
Number 2 in particular prevents mistakes that we will have
to honor later and so is necessary for Go 1.

Fixes #3270.
Fixes #3271.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5795073

src/pkg/text/template/multi_test.go

@@ -93,7 +93,7 @@ var multiExecTests = []execTest{
 	{"invoke dot []int", `{{template "dot" .SI}}`, "[3 4 5]", tVal, true},
 	{"invoke dotV", `{{template "dotV" .U}}`, "v", tVal, true},
 	{"invoke nested int", `{{template "nested" .I}}`, "17", tVal, true},
-	{"variable declared by template", `{{template "nested" $x=.SI}},{{index $x 1}}`, "[3 4 5],4", tVal, true},
+	{"variable declared by template", `{{template "nested" $x:=.SI}},{{index $x 1}}`, "[3 4 5],4", tVal, true},
 
 	// User-defined function: test argument evaluator.
 	{"testFunc literal", `{{oneArg "joe"}}`, "oneArg=joe", tVal, true},

src/pkg/text/template/parse/lex.go

@@ -347,6 +347,9 @@ Loop:
 		default:
 			l.backup()
 			word := l.input[l.start:l.pos]
+			if !l.atTerminator() {
+				return l.errorf("unexpected character %+U", r)
+			}
 			switch {
 			case key[word] > itemKeyword:
 				l.emit(key[word])
@@ -365,6 +368,28 @@ Loop:
 	return lexInsideAction
 }
 
+// atTerminator reports whether the input is at valid termination character to
+// appear after an identifier. Mostly to catch cases like "$x+2" not being
+// acceptable without a space, in case we decide one day to implement
+// arithmetic.
+func (l *lexer) atTerminator() bool {
+	r := l.peek()
+	if isSpace(r) {
+		return true
+	}
+	switch r {
+	case eof, ',', '|', ':':
+		return true
+	}
+	// Does r start the delimiter? This can be ambiguous (with delim=="//", $x/2 will
+	// succeed but should fail) but only in extremely rare cases caused by willfully
+	// bad choice of delimiter.
+	if rd, _ := utf8.DecodeRuneInString(l.rightDelim); rd == r {
+		return true
+	}
+	return false
+}
+
 // lexChar scans a character constant. The initial quote is already
 // scanned.  Syntax checking is done by the parse.
 func lexChar(l *lexer) stateFn {

src/pkg/text/template/parse/parse.go

@@ -326,7 +326,7 @@ func (t *Tree) pipeline(context string) (pipe *PipeNode) {
 	for {
 		if v := t.peek(); v.typ == itemVariable {
 			t.next()
-			if next := t.peek(); next.typ == itemColonEquals || next.typ == itemChar {
+			if next := t.peek(); next.typ == itemColonEquals || (next.typ == itemChar && next.val == ",") {
 				t.next()
 				variable := newVariable(v.val)
 				if len(variable.Ident) != 1 {

src/pkg/text/template/parse/parse_test.go

@@ -201,6 +201,10 @@ var parseTests = []parseTest{
 		`{{range .X | .M}}"true"{{else}}"false"{{end}}`},
 	{"range []int", "{{range .SI}}{{.}}{{end}}", noError,
 		`{{range .SI}}{{.}}{{end}}`},
+	{"range 1 var", "{{range $x := .SI}}{{.}}{{end}}", noError,
+		`{{range $x := .SI}}{{.}}{{end}}`},
+	{"range 2 vars", "{{range $x, $y := .SI}}{{.}}{{end}}", noError,
+		`{{range $x, $y := .SI}}{{.}}{{end}}`},
 	{"constants", "{{range .SI 1 -3.2i true false 'a'}}{{end}}", noError,
 		`{{range .SI 1 -3.2i true false 'a'}}{{end}}`},
 	{"template", "{{template `x`}}", noError,
@@ -226,6 +230,17 @@ var parseTests = []parseTest{
 	{"invalid punctuation", "{{printf 3, 4}}", hasError, ""},
 	{"multidecl outside range", "{{with $v, $u := 3}}{{end}}", hasError, ""},
 	{"too many decls in range", "{{range $u, $v, $w := 3}}{{end}}", hasError, ""},
+	// Equals (and other chars) do not assignments make (yet).
+	{"bug0a", "{{$x := 0}}{{$x}}", noError, "{{$x := 0}}{{$x}}"},
+	{"bug0b", "{{$x = 1}}{{$x}}", hasError, ""},
+	{"bug0c", "{{$x ! 2}}{{$x}}", hasError, ""},
+	{"bug0d", "{{$x % 3}}{{$x}}", hasError, ""},
+	// Check the parse fails for := rather than comma.
+	{"bug0e", "{{range $x := $y := 3}}{{end}}", hasError, ""},
+	// Another bug: variable read must ignore following punctuation.
+	{"bug1a", "{{$x:=.}}{{$x!2}}", hasError, ""},                     // ! is just illegal here.
+	{"bug1b", "{{$x:=.}}{{$x+2}}", hasError, ""},                     // $x+2 should not parse as ($x) (+2).
+	{"bug1c", "{{$x:=.}}{{$x +2}}", noError, "{{$x := .}}{{$x +2}}"}, // It's OK with a space.
 }
 
 var builtins = map[string]interface{}{