exp/template: character constants.

Easier to implement than to justify leaving them out.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/4662089

src/pkg/exp/template/doc.go

@@ -78,10 +78,9 @@ Arguments
 
 An argument is a simple value, denoted by one of the following:
 
-	- A boolean, string, integer, floating-point, imaginary or complex
-	  constant in Go syntax. These behave like Go's untyped constants,
-	  although raw strings may not span newlines. (Character constants are
-	  not supported; this may change.)
+	- A boolean, string, character, integer, floating-point, imaginary
+	  or complex constant in Go syntax. These behave like Go's untyped
+	  constants, although raw strings may not span newlines.
 	- The character '.' (period):
 		.
 	  The result is the value of dot.

src/pkg/exp/template/lex.go

@@ -37,6 +37,7 @@ type itemType int
 const (
 	itemError       itemType = iota // error occurred; value is text of error
 	itemBool                        // boolean constant
+	itemChar                        // character constant
 	itemComplex                     // complex constant (1+2i); imaginary is just a number
 	itemColonEquals                 // colon-equals (':=') introducing a declaration
 	itemEOF
@@ -66,6 +67,7 @@ const (
 var itemName = map[itemType]string{
 	itemError:       "error",
 	itemBool:        "bool",
+	itemChar:        "char",
 	itemComplex:     "complex",
 	itemColonEquals: ":=",
 	itemEOF:         "EOF",
@@ -296,6 +298,8 @@ func lexInsideAction(l *lexer) stateFn {
 			return lexRawQuote
 		case r == '$':
 			return lexIdentifier
+		case r == '\'':
+			return lexChar
 		case r == '.':
 			// special look-ahead for ".field" so we don't break l.backup().
 			if l.pos < len(l.input) {
@@ -348,6 +352,27 @@ Loop:
 	return lexInsideAction
 }
 
+// lexChar scans a character constant. The initial quote is already
+// scanned.  Syntax checking is done by the parse.
+func lexChar(l *lexer) stateFn {
+Loop:
+	for {
+		switch l.next() {
+		case '\\':
+			if r := l.next(); r != eof && r != '\n' {
+				break
+			}
+			fallthrough
+		case eof, '\n':
+			return l.errorf("unterminated character constant")
+		case '\'':
+			break Loop
+		}
+	}
+	l.emit(itemChar)
+	return lexInsideAction
+}
+
 // lexNumber scans a number: decimal, octal, hex, float, or imaginary.  This
 // isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
 // and "089" - but when it's wrong the input is invalid and the parser (via

src/pkg/exp/template/lex_test.go

@@ -53,6 +53,18 @@ var lexTests = []lexTest{
 		tRight,
 		tEOF,
 	}},
+	{"characters", `{{'a' '\n' '\'' '\\' '\u00FF' '\xFF' '本'}}`, []item{
+		tLeft,
+		{itemChar, `'a'`},
+		{itemChar, `'\n'`},
+		{itemChar, `'\''`},
+		{itemChar, `'\\'`},
+		{itemChar, `'\u00FF'`},
+		{itemChar, `'\xFF'`},
+		{itemChar, `'本'`},
+		tRight,
+		tEOF,
+	}},
 	{"bools", "{{true false}}", []item{
 		tLeft,
 		{itemBool, "true"},
@@ -137,6 +149,10 @@ var lexTests = []lexTest{
 		tLeft,
 		{itemError, "unterminated raw quoted string"},
 	}},
+	{"unclosed char constant", "{{'\n}}", []item{
+		tLeft,
+		{itemError, "unterminated character constant"},
+	}},
 	{"bad number", "{{3k}}", []item{
 		tLeft,
 		{itemError, `bad number syntax: "3k"`},

src/pkg/exp/template/parse.go

@@ -289,9 +289,28 @@ type numberNode struct {
 	text       string
 }
 
-func newNumber(text string, isComplex bool) (*numberNode, os.Error) {
+func newNumber(text string, typ itemType) (*numberNode, os.Error) {
 	n := &numberNode{nodeType: nodeNumber, text: text}
-	if isComplex {
+	switch typ {
+	case itemChar:
+		if len(text) < 3 {
+			return nil, fmt.Errorf("illegal character constant: %s", text)
+		}
+		rune, _, tail, err := strconv.UnquoteChar(text[1:len(text)-1], text[0])
+		if err != nil {
+			return nil, err
+		}
+		if len(tail) > 0 {
+			return nil, fmt.Errorf("extra bytes in character constant: %s", text)
+		}
+		n.int64 = int64(rune)
+		n.isInt = true
+		n.uint64 = uint64(rune)
+		n.isUint = true
+		n.float64 = float64(rune) // odd but those are the rules.
+		n.isFloat = true
+		return n, nil
+	case itemComplex:
 		// fmt.Sscan can parse the pair, so let it do the work.
 		if _, err := fmt.Sscan(text, &n.complex128); err != nil {
 			return nil, err
@@ -713,7 +732,7 @@ func (t *Template) pipeline(context string) (pipe *pipeNode) {
 				t.errorf("missing value for %s", context)
 			}
 			return
-		case itemBool, itemComplex, itemDot, itemField, itemIdentifier, itemVariable, itemNumber, itemRawString, itemString:
+		case itemBool, itemChar, itemComplex, itemDot, itemField, itemIdentifier, itemVariable, itemNumber, itemRawString, itemString:
 			t.backup()
 			pipe.append(t.command())
 		default:
@@ -853,8 +872,8 @@ Loop:
 			cmd.append(newField(token.val))
 		case itemBool:
 			cmd.append(newBool(token.val == "true"))
-		case itemComplex, itemNumber:
-			number, err := newNumber(token.val, token.typ == itemComplex)
+		case itemChar, itemComplex, itemNumber:
+			number, err := newNumber(token.val, token.typ)
 			if err != nil {
 				t.error(err)
 			}

src/pkg/exp/template/parse_test.go

@@ -29,6 +29,8 @@ var numberTests = []numberTest{
 	{"0", true, true, true, false, 0, 0, 0, 0},
 	{"-0", true, true, true, false, 0, 0, 0, 0}, // check that -0 is a uint.
 	{"73", true, true, true, false, 73, 73, 73, 0},
+	{"073", true, true, true, false, 073, 073, 073, 0},
+	{"0x73", true, true, true, false, 0x73, 0x73, 0x73, 0},
 	{"-73", true, false, true, false, -73, 0, -73, 0},
 	{"+73", true, false, true, false, 73, 0, 73, 0},
 	{"100", true, true, true, false, 100, 100, 100, 0},
@@ -39,6 +41,7 @@ var numberTests = []numberTest{
 	{"-1e19", false, false, true, false, 0, 0, -1e19, 0},
 	{"4i", false, false, false, true, 0, 0, 0, 4i},
 	{"-1.2+4.2i", false, false, false, true, 0, 0, 0, -1.2 + 4.2i},
+	{"073i", false, false, false, true, 0, 0, 0, 73i}, // not octal!
 	// complex with 0 imaginary are float (and maybe integer)
 	{"0i", true, true, true, true, 0, 0, 0, 0},
 	{"-1.2+0i", false, false, true, true, 0, 0, -1.2, -1.2},
@@ -48,12 +51,23 @@ var numberTests = []numberTest{
 	{"0123", true, true, true, false, 0123, 0123, 0123, 0},
 	{"-0x0", true, true, true, false, 0, 0, 0, 0},
 	{"0xdeadbeef", true, true, true, false, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0},
+	// character constants
+	{`'a'`, true, true, true, false, 'a', 'a', 'a', 0},
+	{`'\n'`, true, true, true, false, '\n', '\n', '\n', 0},
+	{`'\\'`, true, true, true, false, '\\', '\\', '\\', 0},
+	{`'\''`, true, true, true, false, '\'', '\'', '\'', 0},
+	{`'\xFF'`, true, true, true, false, 0xFF, 0xFF, 0xFF, 0},
+	{`'パ'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
+	{`'\u30d1'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
+	{`'\U000030d1'`, true, true, true, false, 0x30d1, 0x30d1, 0x30d1, 0},
 	// some broken syntax
 	{text: "+-2"},
 	{text: "0x123."},
 	{text: "1e."},
 	{text: "0xi."},
 	{text: "1+2."},
+	{text: "'x"},
+	{text: "'xx'"},
 }
 
 func TestNumberParse(t *testing.T) {
@@ -61,11 +75,19 @@ func TestNumberParse(t *testing.T) {
 		// If fmt.Sscan thinks it's complex, it's complex.  We can't trust the output
 		// because imaginary comes out as a number.
 		var c complex128
-		_, err := fmt.Sscan(test.text, &c)
-		n, err := newNumber(test.text, err == nil)
+		typ := itemNumber
+		if test.text[0] == '\'' {
+			typ = itemChar
+		} else {
+			_, err := fmt.Sscan(test.text, &c)
+			if err == nil {
+				typ = itemComplex
+			}
+		}
+		n, err := newNumber(test.text, typ)
 		ok := test.isInt || test.isUint || test.isFloat || test.isComplex
 		if ok && err != nil {
-			t.Errorf("unexpected error for %q", test.text)
+			t.Errorf("unexpected error for %q: %s", test.text, err)
 			continue
 		}
 		if !ok && err == nil {
@@ -73,6 +95,9 @@ func TestNumberParse(t *testing.T) {
 			continue
 		}
 		if !ok {
+			if *debug {
+				fmt.Printf("%s\n\t%s\n", test.text, err)
+			}
 			continue
 		}
 		if n.isComplex != test.isComplex {
@@ -174,8 +199,8 @@ var parseTests = []parseTest{
 		`[({{range [(command: [F=[X]]) (command: [F=[M]])]}} [(text: "true")] {{else}} [(text: "false")])]`},
 	{"range []int", "{{range .SI}}{{.}}{{end}}", noError,
 		`[({{range [(command: [F=[SI]])]}} [(action: [(command: [{{<.>}}])])])]`},
-	{"constants", "{{range .SI 1 -3.2i true false }}{{end}}", noError,
-		`[({{range [(command: [F=[SI] N=1 N=-3.2i B=true B=false])]}} [])]`},
+	{"constants", "{{range .SI 1 -3.2i true false 'a'}}{{end}}", noError,
+		`[({{range [(command: [F=[SI] N=1 N=-3.2i B=true B=false N='a'])]}} [])]`},
 	{"template", "{{template `x`}}", noError,
 		"[{{template S=`x`}}]"},
 	{"template", "{{template `x` .Y}}", noError,