First cut at templating library for text generation

R=rsc
DELTA=663  (663 added, 0 deleted, 0 changed)
OCL=27239
CL=27241

src/lib/Makefile

@@ -36,6 +36,7 @@ FILES=\
 	rand\
 	sort\
 	strings\
+	template\
 	testing\
 	utf8\
 
@@ -48,6 +49,7 @@ TEST=\
 	once\
 	sort\
 	strings\
+	template\
 	utf8\
 
 clean.dirs: $(addsuffix .dirclean, $(DIRS))
@@ -99,6 +101,7 @@ log.6: fmt.dirinstall io.dirinstall os.dirinstall time.dirinstall
 path.6: io.dirinstall
 once.6: sync.dirinstall
 strings.6: utf8.install
+template.6: bufio.install fmt.dirinstall io.dirinstall os.dirinstall reflect.dirinstall strings.install
 testing.6: flag.install fmt.dirinstall
 
 fmt.dirinstall: io.dirinstall reflect.dirinstall strconv.dirinstall

src/lib/template.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Template library.  See http://code.google.com/p/json-template/wiki/Reference
+// TODO: document this here as well.
+
+package template
+
+import (
+	"bufio";
+	"fmt";
+	"io";
+	"os";
+	"reflect";
+	"strings";
+)
+
+var ErrLBrace = os.NewError("unexpected opening brace")
+var ErrUnmatchedRBrace = os.NewError("unmatched closing brace")
+var ErrUnmatchedLBrace = os.NewError("unmatched opening brace")
+var ErrBadDirective = os.NewError("unrecognized directive name")
+var ErrEmptyDirective = os.NewError("empty directive")
+var ErrFields = os.NewError("incorrect fields for directive")
+var ErrSyntax = os.NewError("directive out of place")
+var ErrNoEnd = os.NewError("section does not have .end")
+var ErrNoVar = os.NewError("variable name not in struct");
+var ErrBadType = os.NewError("unsupported type for variable");
+var ErrNotStruct = os.NewError("driver must be a struct")
+
+// All the literals are aces.
+var lbrace = []byte{ '{' }
+var rbrace = []byte{ '}' }
+var space = []byte{ ' ' }
+
+// The various types of "tokens", which are plain text or brace-delimited descriptors
+const (
+	Alternates = iota;
+	Comment;
+	End;
+	Literal;
+	Or;
+	Repeated;
+	Section;
+	Text;
+	Variable;
+)
+
+type template struct {
+	errorchan	chan *os.Error;	// for erroring out
+	linenum	*int;	// shared by all templates derived from this one
+	parent	*template;
+	data	reflect.Value;	// the driver data for this section etc.
+	buf	[]byte;	// input text to process
+	p	int;	// position in buf
+	wr	io.Write;	// where to send output
+}
+
+// Create a top-level template
+func newTemplate(ch chan *os.Error, linenum *int, buf []byte, data reflect.Value, wr io.Write) *template {
+	t := new(template);
+	t.errorchan = ch;
+	t.linenum = linenum;
+	*linenum = 1;
+	t.parent = nil;
+	t.data = data;
+	t.buf = buf;
+	t.p = 0;
+	t.wr = wr;
+	return t;
+}
+
+// Create a template deriving from its parent
+func childTemplate(parent *template, buf []byte, data reflect.Value) *template {
+	t := newTemplate(parent.errorchan, parent.linenum, buf, data, parent.wr);
+	t.parent = parent;
+	return t;
+}
+
+// Report error and stop generation.
+func (t *template) error(err *os.Error, args ...) {
+	fmt.Fprintf(os.Stderr, "template error: line %d: %s%s\n", *t.linenum, err, fmt.Sprint(args));  // TODO: drop this? (only way to get line number)
+	t.errorchan <- err;
+	sys.Goexit();
+}
+
+func white(c uint8) bool {
+	return c == ' ' || c == '\t' || c == '\n'
+}
+
+// Data items can be values or pointers to values. This function hides the pointer.
+func indirect(v reflect.Value) reflect.Value {
+	if v.Kind() == reflect.PtrKind {
+		p := v.(reflect.PtrValue);
+		if p.Get() == nil {
+			return nil
+		}
+		v = p.Sub()
+	}
+	return v
+}
+
+func (t *template) execute()
+func (t *template) executeSection(w []string)
+
+// nextItem returns the next item from the input buffer.  If the returned
+// item is empty, we are at EOF.  The item will be either a brace-
+// delimited string or a non-empty string between brace-delimited
+// strings.  Most tokens stop at (but include, if plain text) a newline.
+// Action tokens on a line by themselves drop the white space on
+// either side, up to and including the newline.
+func (t *template) nextItem() []byte {
+	brace := false;	// are we waiting for an opening brace?
+	special := false;	// is this a {.foo} directive, which means trim white space?
+	// Delete surrounding white space if this {.foo} is the only thing on the line.
+	trim_white := t.p == 0 || t.buf[t.p-1] == '\n';
+	only_white := true;	// we have seen only white space so far
+	var i int;
+	start := t.p;
+Loop:
+	for i = t.p; i < len(t.buf); i++ {
+		switch t.buf[i] {
+		case '\n':
+			*t.linenum++;
+			i++;
+			break Loop;
+		case ' ', '\t':
+			// white space, do nothing
+		case '{':
+			if brace {
+				t.error(ErrLBrace)
+			}
+			// anything interesting already on the line?
+			if !only_white {
+				break Loop;
+			}
+			// is it a directive or comment?
+			if i+2 < len(t.buf) && (t.buf[i+1] == '.' || t.buf[i+1] == '#') {
+				special = true;
+				if trim_white && only_white {
+					start = i;
+				}
+			} else if i > t.p+1 {  // have some text accumulated so stop before '{'
+				break Loop;
+			}
+			brace = true;
+		case '}':
+			if !brace {
+				t.error(ErrUnmatchedRBrace)
+			}
+			brace = false;
+			i++;
+			break Loop;
+		default:
+			only_white = false;
+		}
+	}
+	if brace {
+		t.error(ErrUnmatchedLBrace)
+	}
+	item := t.buf[start:i];
+	if special && trim_white {
+		// consume trailing white space
+		for ; i < len(t.buf) && white(t.buf[i]); i++ {
+			if t.buf[i] == '\n' {
+				i++;
+				break	// stop after newline
+			}
+		}
+	}
+	t.p = i;
+	return item
+}
+
+// Turn a byte array into a white-space-split array of strings.
+func words(buf []byte) []string {
+	s := make([]string, 0, 5);
+	p := 0; // position in buf
+	// one word per loop
+	for i := 0; ; i++ {
+		// skip white space
+		for ; p < len(buf) && white(buf[p]); p++ {
+		}
+		// grab word
+		start := p;
+		for ; p < len(buf) && !white(buf[p]); p++ {
+		}
+		if start == p {	// no text left
+			break
+		}
+		if i == cap(s) {
+			ns := make([]string, 2*cap(s));
+			for j := range s {
+				ns[j] = s[j]
+			}
+			s = ns;
+		}
+		s = s[0:i+1];
+		s[i] = string(buf[start:p])
+	}
+	return s
+}
+
+// Analyze an item and return its type and, if it's an action item, an array of
+// its constituent words.
+func (t *template) analyze(item []byte) (tok int, w []string) {
+	// item is known to be non-empty
+	if item[0] != '{' {
+		tok = Text;
+		return
+	}
+	if item[len(item)-1] != '}' {
+		t.error(ErrUnmatchedLBrace)  // should not happen anyway
+	}
+	if len(item) <= 2 {
+		t.error(ErrEmptyDirective)
+	}
+	// Comment
+	if item[1] == '#' {
+		tok = Comment;
+		return
+	}
+	// Split into words
+	w = words(item[1: len(item)-1]);  // drop final brace
+	if len(w) == 0 {
+		t.error(ErrBadDirective)
+	}
+	if len(w[0]) == 0 {
+		t.error(ErrEmptyDirective)
+	}
+	if len(w) == 1 && w[0][0] != '.' {
+		tok = Variable;
+		return;
+	}
+	switch w[0] {
+	case ".meta-left", ".meta-right", ".space":
+		tok = Literal;
+		return;
+	case ".or":
+		tok = Or;
+		return;
+	case ".end":
+		tok = End;
+		return;
+	case ".section":
+		if len(w) != 2 {
+			t.error(ErrFields, ": ", string(item))
+		}
+		tok = Section;
+		return;
+	case ".repeated":
+		if len(w) != 3 || w[1] != "section" {
+			t.error(ErrFields, ": ", string(item))
+		}
+		tok = Repeated;
+		return;
+	case ".alternates":
+		if len(w) != 2 || w[1] != "with" {
+			t.error(ErrFields, ": ", string(item))
+		}
+		tok = Alternates;
+		return;
+	}
+	t.error(ErrBadDirective, ": ", string(item));
+	return
+}
+
+// If the data for this template is a struct, find the named variable.
+func (t *template) findVar(s string) (int, int) {
+	typ, ok := t.data.Type().(reflect.StructType);
+	if ok {
+		for i := 0; i < typ.Len(); i++ {
+			name, ftyp, tag, offset := typ.Field(i);
+			if name == s {
+				return i, ftyp.Kind()
+			}
+		}
+	}
+	return -1, -1
+}
+
+// Is there no data to look at?
+func empty(v reflect.Value, indirect_ok bool) bool {
+	v = indirect(v);
+	if v == nil {
+		return true
+	}
+	switch v.Type().Kind() {
+	case reflect.StructKind:
+		return false;
+	case reflect.ArrayKind:
+		return v.(reflect.ArrayValue).Len() == 0;
+	}
+	return true;
+}
+
+// Execute a ".repeated" section
+func (t *template) executeRepeated(w []string) {
+	if w[1] != "section" {
+		t.error(ErrSyntax, `: .repeated must have "section"`)
+	}
+	// Find driver array/struct for this section.  It must be in the current struct.
+	// The special name "@" leaves us at this level.
+	var field reflect.Value;
+	if w[2] == "@" {
+		field = t.data
+	} else {
+		i, kind := t.findVar(w[1]);
+		if i < 0 {
+			t.error(ErrNoVar, ": ", w[2]);
+		}
+		field = indirect(t.data.(reflect.StructValue).Field(i));
+	}
+	// Must be an array/slice
+	if field != nil && field.Kind() != reflect.ArrayKind {
+		t.error(ErrBadType, " in .repeated: ", w[2], " ", field.Type().String());
+	}
+	// Scan repeated section, remembering slice of text we must execute.
+	nesting := 0;
+	start := t.p;
+	end := t.p;
+Loop:
+	for {
+		item := t.nextItem();
+		if len(item) ==  0 {
+			t.error(ErrNoEnd)
+		}
+		tok, s := t.analyze(item);
+		switch tok {
+		case Comment:
+			continue;	// just ignore it
+		case End:
+			if nesting == 0 {
+				break Loop
+			}
+			nesting--;
+		case Repeated, Section:
+			nesting++;
+		case Literal, Or, Text, Variable:
+			// just accumulate
+		default:
+			panic("unknown section item", string(item));
+		}
+		end = t.p
+	}
+	if field != nil {
+		array := field.(reflect.ArrayValue);
+		for i := 0; i < array.Len(); i++ {
+			elem := indirect(array.Elem(i));
+			tmp := childTemplate(t, t.buf[start:end], elem);
+			tmp.execute();
+		}
+	}
+}
+
+// Execute a ".section"
+func (t *template) executeSection(w []string) {
+	// Find driver array/struct for this section.  It must be in the current struct.
+	// The special name "@" leaves us at this level.
+	var field reflect.Value;
+	if w[1] == "@" {
+		field = t.data
+	} else {
+		i, kind := t.findVar(w[1]);
+		if i < 0 {
+			t.error(ErrNoVar, ": ", w[1]);
+		}
+		field = t.data.(reflect.StructValue).Field(i);
+	}
+	// Scan section, remembering slice of text we must execute.
+	orFound := false;
+	nesting := 0;  // How deeply are .section and .repeated nested?
+	start := t.p;
+	end := t.p;
+	accumulate := !empty(field, true);	// Keep this section if there's data
+Loop:
+	for {
+		item := t.nextItem();
+		if len(item) ==  0 {
+			t.error(ErrNoEnd)
+		}
+		tok, s := t.analyze(item);
+		switch tok {
+		case Comment:
+			continue;	// just ignore it
+		case End:
+			if nesting == 0 {
+				break Loop
+			}
+			nesting--;
+		case Or:
+			if nesting > 0 {	// just accumulate
+				break
+			}
+			if orFound {
+				t.error(ErrSyntax, ": .or");
+			}
+			orFound = true;
+			if !accumulate {
+				// No data; execute the .or instead
+				start = t.p;
+				end = t.p;
+				accumulate = true;
+				continue;
+			} else {
+				// Data present so disregard the .or section
+				accumulate = false
+			}
+		case Repeated, Section:
+			nesting++;
+		case Literal, Text, Variable:
+			// just accumulate
+		default:
+			panic("unknown section item", string(item));
+		}
+		if accumulate {
+			end = t.p
+		}
+	}
+	tmp := childTemplate(t, t.buf[start:end], field);
+	tmp.execute();
+}
+
+// Evalute a variable, looking up through the parent if necessary.
+// TODO: add formatting outputters
+func (t *template) evalVariable(s string) string {
+	i, kind := t.findVar(s);
+	if i < 0 {
+		if t.parent == nil {
+			t.error(ErrNoVar, ": ", s)
+		}
+		return t.parent.evalVariable(s);
+	}
+	return fmt.Sprint(t.data.(reflect.StructValue).Field(i).Interface());
+}
+
+func (t *template) execute() {
+	for {
+		item := t.nextItem();
+		if len(item) == 0 {
+			return
+		}
+		tok, w := t.analyze(item);
+		switch tok {
+		case Comment:
+			break;
+		case Text:
+			t.wr.Write(item);
+		case Literal:
+			switch w[0] {
+			case ".meta-left":
+				t.wr.Write(lbrace);
+			case ".meta-right":
+				t.wr.Write(rbrace);
+			case ".space":
+				t.wr.Write(space);
+			default:
+				panic("unknown literal: ", w[0]);
+			}
+		case Variable:
+			t.wr.Write(io.StringBytes(t.evalVariable(w[0])));
+		case Or, End, Alternates:
+			t.error(ErrSyntax, ": ", string(item));
+		case Section:
+			t.executeSection(w);
+		case Repeated:
+			t.executeRepeated(w);
+		default:
+			panic("bad directive in execute:", string(item));
+		}
+	}
+}
+
+func Execute(s string, data interface{}, wr io.Write) *os.Error {
+	// Extract the driver struct.
+	val := indirect(reflect.NewValue(data));
+	sval, ok1 := val.(reflect.StructValue);
+	if !ok1 {
+		return ErrNotStruct
+	}
+	ch := make(chan *os.Error);
+	var linenum int;
+	t := newTemplate(ch, &linenum, io.StringBytes(s), val, wr);
+	go func() {
+		t.execute();
+		ch <- nil;	// clean return;
+	}();
+	return <-ch;
+}

src/lib/template_test.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"fmt";
+	"io";
+	"os";
+	"template";
+	"testing";
+)
+
+type Test struct {
+	in, out string
+}
+
+type T struct {
+	item string;
+	value string;
+}
+
+type S struct {
+	header string;
+	integer int;
+	data []T;
+	pdata []*T;
+	empty []*T;
+	null []*T;
+}
+
+var t1 = T{ "ItemNumber1", "ValueNumber1" }
+var t2 = T{ "ItemNumber2", "ValueNumber2" }
+
+var tests = []*Test {
+	// Simple
+	&Test{ "", "" },
+	&Test{ "abc\ndef\n", "abc\ndef\n" },
+	&Test{ " {.meta-left}   \n", "{" },
+	&Test{ " {.meta-right}   \n", "}" },
+	&Test{ " {.space}   \n", " " },
+	&Test{ "     {#comment}   \n", "" },
+
+	// Section
+	&Test{
+		"{.section data }\n"
+		"some text for the section\n"
+		"{.end}\n",
+
+		"some text for the section\n"
+	},
+	&Test{
+		"{.section data }\n"
+		"{header}={integer}\n"
+		"{.end}\n",
+
+		"Header=77\n"
+	},
+	&Test{
+		"{.section pdata }\n"
+		"{header}={integer}\n"
+		"{.end}\n",
+
+		"Header=77\n"
+	},
+	&Test{
+		"{.section pdata }\n"
+		"data present\n"
+		"{.or}\n"
+		"data not present\n"
+		"{.end}\n",
+
+		"data present\n"
+	},
+	&Test{
+		"{.section empty }\n"
+		"data present\n"
+		"{.or}\n"
+		"data not present\n"
+		"{.end}\n",
+
+		"data not present\n"
+	},
+	&Test{
+		"{.section null }\n"
+		"data present\n"
+		"{.or}\n"
+		"data not present\n"
+		"{.end}\n",
+
+		"data not present\n"
+	},
+	&Test{
+		"{.section pdata }\n"
+		"{header}={integer}\n"
+		"{.section @ }\n"
+		"{header}={integer}\n"
+		"{.end}\n"
+		"{.end}\n",
+
+		"Header=77\n"
+		"Header=77\n"
+	},
+
+	// Repeated
+	&Test{
+		"{.section pdata }\n"
+		"{.repeated section @ }\n"
+		"{item}={value}\n"
+		"{.end}\n"
+		"{.end}\n",
+
+		"ItemNumber1=ValueNumber1\n"
+		"ItemNumber2=ValueNumber2\n"
+	},
+}
+
+func TestAll(t *testing.T) {
+	s := new(S);
+	// initialized by hand for clarity.
+	s.header = "Header";
+	s.integer = 77;
+	s.data = []T{ t1, t2 };
+	s.pdata = []*T{ &t1, &t2 };
+	s.empty = []*T{ };
+	s.null = nil;
+
+	var buf io.ByteBuffer;
+	for i, test := range tests {
+		buf.Reset();
+		err := Execute(test.in, s, &buf);
+		if err != nil {
+			t.Error("unexpected error:", err)
+		}
+		if string(buf.Data()) != test.out {
+			t.Errorf("for %q: expected %q got %q", test.in, test.out, string(buf.Data()));
+		}
+	}
+}
+
+/*
+func TestParser(t *testing.T) {
+	t1 := &T{ "ItemNumber1", "ValueNumber1" };
+	t2 := &T{ "ItemNumber2", "ValueNumber2" };
+	a := []*T{ t1, t2 };
+	s := &S{ "Header", 77, a };
+	err := Execute(
+		"{#hello world}\n"
+		"some text: {.meta-left}{.space}{.meta-right}\n"
+		"{.meta-left}\n"
+		"{.meta-right}\n"
+		"{.section data }\n"
+		"some text for the section\n"
+		"{header} for iteration number {integer}\n"
+		"	{.repeated section @}\n"
+		"repeated section: {value1}={value2}\n"
+		"	{.end}\n"
+		"{.or}\n"
+		"This appears only if there is no data\n"
+		"{.end }\n"
+		"this is the end\n"
+		, s, os.Stdout);
+	if err != nil {
+		t.Error(err)
+	}
+}
+*/
+
+func TestBadDriverType(t *testing.T) {
+	err := Execute("hi", "hello", os.Stdout);
+	if err == nil {
+		t.Error("failed to detect string as driver type")
+	}
+	var s S;
+}