exp/template: functions

Add the ability to attach functions to template and template sets.
Make variadic functions and methods work.
Still to come: static checking of function names during parse.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/4643068

6 files changed, 196 insertions, 39 deletions

diff --git a/src/pkg/exp/template/Makefile b/src/pkg/exp/template/Makefile
index 50a0bd7234..8550b0d522 100644
--- a/src/pkg/exp/template/Makefile
+++ b/src/pkg/exp/template/Makefile
@@ -7,6 +7,7 @@ include ../../../Make.inc
 TARG=exp/template
 GOFILES=\
 	exec.go\
+	funcs.go\
 	lex.go\
 	parse.go\
 	set.go\
diff --git a/src/pkg/exp/template/exec.go b/src/pkg/exp/template/exec.go
index 3eaecd1941..636bc4c334 100644
--- a/src/pkg/exp/template/exec.go
+++ b/src/pkg/exp/template/exec.go
@@ -174,8 +174,11 @@ func (s *state) evalPipeline(data reflect.Value, pipe []*commandNode) reflect.Va
 
 func (s *state) evalCommand(data reflect.Value, cmd *commandNode, final reflect.Value) reflect.Value {
 	firstWord := cmd.args[0]
-	if field, ok := firstWord.(*fieldNode); ok {
-		return s.evalFieldNode(data, field, cmd.args, final)
+	switch n := firstWord.(type) {
+	case *fieldNode:
+		return s.evalFieldNode(data, n, cmd.args, final)
+	case *identifierNode:
+		return s.evalFieldOrCall(data, n.ident, cmd.args, final)
 	}
 	if len(cmd.args) > 1 || final.IsValid() {
 		// TODO: functions
@@ -215,7 +218,7 @@ func (s *state) evalFieldNode(data reflect.Value, field *fieldNode, args []node,
 		data = s.evalField(data, field.ident[i])
 	}
 	// Now it can be a field or method and if a method, gets arguments.
-	return s.evalMethodOrField(data, field.ident[n-1], args, final)
+	return s.evalFieldOrCall(data, field.ident[n-1], args, final)
 }
 
 func (s *state) evalField(data reflect.Value, fieldName string) reflect.Value {
@@ -238,14 +241,18 @@ func (s *state) evalField(data reflect.Value, fieldName string) reflect.Value {
 	panic("not reached")
 }
 
-func (s *state) evalMethodOrField(data reflect.Value, fieldName string, args []node, final reflect.Value) reflect.Value {
+func (s *state) evalFieldOrCall(data reflect.Value, fieldName string, args []node, final reflect.Value) reflect.Value {
+	// Is it a function?
+	if function, ok := findFunction(fieldName, s.tmpl, s.set); ok {
+		return s.evalCall(data, function, fieldName, false, args, final)
+	}
 	ptr := data
 	for data.Kind() == reflect.Ptr {
 		ptr, data = data, reflect.Indirect(data)
 	}
 	// Is it a method? We use the pointer because it has value methods too.
 	if method, ok := ptr.Type().MethodByName(fieldName); ok {
-		return s.evalMethod(ptr, method, args, final)
+		return s.evalCall(ptr, method.Func, fieldName, true, args, final)
 	}
 	if len(args) > 1 || final.IsValid() {
 		s.errorf("%s is not a method but has arguments", fieldName)
@@ -263,31 +270,46 @@ var (
 	osErrorType = reflect.TypeOf(new(os.Error)).Elem()
 )
 
-func (s *state) evalMethod(v reflect.Value, method reflect.Method, args []node, final reflect.Value) reflect.Value {
-	typ := method.Type
-	fun := method.Func
+func (s *state) evalCall(v, fun reflect.Value, name string, isMethod bool, args []node, final reflect.Value) reflect.Value {
+	typ := fun.Type()
+	if !isMethod && len(args) > 0 { // Args will be nil if it's a niladic call in an argument list
+		args = args[1:] // first arg is name of function; not used in call.
+	}
 	numIn := len(args)
 	if final.IsValid() {
 		numIn++
 	}
-	if !typ.IsVariadic() && numIn < typ.NumIn()-1 || !typ.IsVariadic() && numIn != typ.NumIn() {
-		s.errorf("wrong number of args for %s: want %d got %d", method.Name, typ.NumIn(), len(args))
+	numFixed := len(args)
+	if typ.IsVariadic() {
+		numFixed = typ.NumIn() - 1 // last arg is the variadic one.
+		if numIn < numFixed {
+			s.errorf("wrong number of args for %s: want at least %d got %d", name, typ.NumIn()-1, len(args))
+		}
+	} else if numIn < typ.NumIn()-1 || !typ.IsVariadic() && numIn != typ.NumIn() {
+		s.errorf("wrong number of args for %s: want %d got %d", name, typ.NumIn(), len(args))
 	}
-	// We allow methods with 1 result or 2 results where the second is an os.Error.
-	switch {
-	case typ.NumOut() == 1:
-	case typ.NumOut() == 2 && typ.Out(1) == osErrorType:
-	default:
-		s.errorf("can't handle multiple results from method %q", method.Name)
+	if !goodFunc(typ) {
+		s.errorf("can't handle multiple results from method/function %q", name)
 	}
 	// Build the arg list.
 	argv := make([]reflect.Value, numIn)
 	// First arg is the receiver.
-	argv[0] = v
-	// Others must be evaluated.
-	for i := 1; i < len(args); i++ {
+	i := 0
+	if isMethod {
+		argv[0] = v
+		i++
+	}
+	// Others must be evaluated. Fixed args first.
+	for ; i < numFixed; i++ {
 		argv[i] = s.evalArg(v, typ.In(i), args[i])
 	}
+	// And now the ... args.
+	if typ.IsVariadic() {
+		argType := typ.In(typ.NumIn() - 1).Elem() // Argument is a slice.
+		for ; i < len(args); i++ {
+			argv[i] = s.evalArg(v, argType, args[i])
+		}
+	}
 	// Add final value if necessary.
 	if final.IsValid() {
 		argv[len(args)] = final
@@ -310,23 +332,27 @@ func (s *state) evalArg(data reflect.Value, typ reflect.Type, n node) reflect.Va
 	}
 	switch typ.Kind() {
 	case reflect.Bool:
-		return s.evalBool(data, typ, n)
+		return s.evalBool(typ, n)
 	case reflect.String:
-		return s.evalString(data, typ, n)
+		return s.evalString(typ, n)
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return s.evalInteger(data, typ, n)
+		return s.evalInteger(typ, n)
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		return s.evalUnsignedInteger(data, typ, n)
+		return s.evalUnsignedInteger(typ, n)
 	case reflect.Float32, reflect.Float64:
-		return s.evalFloat(data, typ, n)
+		return s.evalFloat(typ, n)
 	case reflect.Complex64, reflect.Complex128:
-		return s.evalComplex(data, typ, n)
+		return s.evalComplex(typ, n)
+	case reflect.Interface:
+		if typ.NumMethod() == 0 {
+			return s.evalEmptyInterface(data, typ, n)
+		}
 	}
-	s.errorf("can't handle node %s for method arg of type %s", n, typ)
+	s.errorf("can't handle %s for arg of type %s", n, typ)
 	panic("not reached")
 }
 
-func (s *state) evalBool(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalBool(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*boolNode); ok {
 		value := reflect.New(typ).Elem()
 		value.SetBool(n.true)
@@ -336,7 +362,7 @@ func (s *state) evalBool(v reflect.Value, typ reflect.Type, n node) reflect.Valu
 	panic("not reached")
 }
 
-func (s *state) evalString(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalString(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*stringNode); ok {
 		value := reflect.New(typ).Elem()
 		value.SetString(n.text)
@@ -346,7 +372,7 @@ func (s *state) evalString(v reflect.Value, typ reflect.Type, n node) reflect.Va
 	panic("not reached")
 }
 
-func (s *state) evalInteger(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalInteger(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*numberNode); ok && n.isInt {
 		value := reflect.New(typ).Elem()
 		value.SetInt(n.int64)
@@ -356,7 +382,7 @@ func (s *state) evalInteger(v reflect.Value, typ reflect.Type, n node) reflect.V
 	panic("not reached")
 }
 
-func (s *state) evalUnsignedInteger(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalUnsignedInteger(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*numberNode); ok && n.isUint {
 		value := reflect.New(typ).Elem()
 		value.SetUint(n.uint64)
@@ -366,7 +392,7 @@ func (s *state) evalUnsignedInteger(v reflect.Value, typ reflect.Type, n node) r
 	panic("not reached")
 }
 
-func (s *state) evalFloat(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalFloat(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*numberNode); ok && n.isFloat {
 		value := reflect.New(typ).Elem()
 		value.SetFloat(n.float64)
@@ -376,7 +402,7 @@ func (s *state) evalFloat(v reflect.Value, typ reflect.Type, n node) reflect.Val
 	panic("not reached")
 }
 
-func (s *state) evalComplex(v reflect.Value, typ reflect.Type, n node) reflect.Value {
+func (s *state) evalComplex(typ reflect.Type, n node) reflect.Value {
 	if n, ok := n.(*numberNode); ok && n.isComplex {
 		value := reflect.New(typ).Elem()
 		value.SetComplex(n.complex128)
@@ -386,6 +412,34 @@ func (s *state) evalComplex(v reflect.Value, typ reflect.Type, n node) reflect.V
 	panic("not reached")
 }
 
+func (s *state) evalEmptyInterface(data reflect.Value, typ reflect.Type, n node) reflect.Value {
+	switch n := n.(type) {
+	case *boolNode:
+		return reflect.ValueOf(n.true)
+	case *fieldNode:
+		return s.evalFieldNode(data, n, nil, reflect.Value{})
+	case *identifierNode:
+		return s.evalFieldOrCall(data, n.ident, nil, reflect.Value{})
+	case *numberNode:
+		if n.isComplex {
+			return reflect.ValueOf(n.complex128)
+		}
+		if n.isInt {
+			return reflect.ValueOf(n.int64)
+		}
+		if n.isUint {
+			return reflect.ValueOf(n.uint64)
+		}
+		if n.isFloat {
+			return reflect.ValueOf(n.float64)
+		}
+	case *stringNode:
+		return reflect.ValueOf(n.text)
+	}
+	s.errorf("can't handle assignment of %s to empty interface argument", n)
+	panic("not reached")
+}
+
 // printValue writes the textual representation of the value to the output of
 // the template.
 func (s *state) printValue(n node, v reflect.Value) {
diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go
index 6e4da692e9..8784a0b9fd 100644
--- a/src/pkg/exp/template/exec_test.go
+++ b/src/pkg/exp/template/exec_test.go
@@ -140,6 +140,16 @@ var execTests = []execTest{
 	{"if slice", "{{if .SI}}NON-EMPTY{{else}}EMPTY{{end}}", "NON-EMPTY", tVal, true},
 	{"if emptymap", "{{if .MSIEmpty}}NON-EMPTY{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
 	{"if map", "{{if .MSI}}NON-EMPTY{{else}}EMPTY{{end}}", "NON-EMPTY", tVal, true},
+	// Function calls.
+	{"printf", `{{printf "hello, printf"}}`, "hello, printf", tVal, true},
+	{"printf int", `{{printf "%04x" 127}}`, "007f", tVal, true},
+	{"printf float", `{{printf "%g" 3.5}}`, "3.5", tVal, true},
+	{"printf complex", `{{printf "%g" 1+7i}}`, "(1+7i)", tVal, true},
+	{"printf string", `{{printf "%s" "hello"}}`, "hello", tVal, true},
+	{"printf function", `{{printf "%#q" gopher}}`, "`gopher`", tVal, true},
+	{"printf field", `{{printf "%s" .U.V}}`, "v", tVal, true},
+	{"printf method", `{{printf "%s" .Method0}}`, "resultOfMethod0", tVal, true},
+	{"printf lots", `{{printf "%d %s %g %s" 127 "hello" 7-3i .Method0}}`, "127 hello (7-3i) resultOfMethod0", tVal, true},
 	// With.
 	{"with true", "{{with true}}{{.}}{{end}}", "true", tVal, true},
 	{"with false", "{{with false}}{{.}}{{else}}FALSE{{end}}", "FALSE", tVal, true},
@@ -171,10 +181,15 @@ var execTests = []execTest{
 	{"error method, no error", "{{.EPERM false}}", "false", tVal, true},
 }
 
+func gopher() string {
+	return "gopher"
+}
+
 func testExecute(execTests []execTest, set *Set, t *testing.T) {
 	b := new(bytes.Buffer)
+	funcs := FuncMap{"gopher": gopher}
 	for _, test := range execTests {
-		tmpl := New(test.name)
+		tmpl := New(test.name).Funcs(funcs)
 		err := tmpl.Parse(test.input)
 		if err != nil {
 			t.Errorf("%s: parse error: %s", test.name, err)
diff --git a/src/pkg/exp/template/funcs.go b/src/pkg/exp/template/funcs.go
new file mode 100644
index 0000000000..88f82f3b2c
--- /dev/null
+++ b/src/pkg/exp/template/funcs.go
@@ -0,0 +1,63 @@
+// Copyright 2011 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"
+	"reflect"
+)
+
+// FuncMap is the type of the map defining the mapping from names to functions.
+// Each function must have either a single return value, or two return values of
+// which the second has type os.Error.
+type FuncMap map[string]interface{}
+
+var funcs = map[string]reflect.Value{
+	"printf": reflect.ValueOf(fmt.Sprintf),
+}
+
+// addFuncs adds to values the functions in funcs, converting them to reflect.Values.
+func addFuncs(values map[string]reflect.Value, funcMap FuncMap) {
+	for name, fn := range funcMap {
+		v := reflect.ValueOf(fn)
+		if v.Kind() != reflect.Func {
+			panic("value for " + name + " not a function")
+		}
+		if !goodFunc(v.Type()) {
+			panic(fmt.Errorf("can't handle multiple results from method/function %q", name))
+		}
+		values[name] = v
+	}
+}
+
+// goodFunc checks that the function or method has the right result signature.
+func goodFunc(typ reflect.Type) bool {
+	// We allow functions with 1 result or 2 results where the second is an os.Error.
+	switch {
+	case typ.NumOut() == 1:
+		return true
+	case typ.NumOut() == 2 && typ.Out(1) == osErrorType:
+		return true
+	}
+	return false
+}
+
+// findFunction looks for a function in the template, set, and global map.
+func findFunction(name string, tmpl *Template, set *Set) (reflect.Value, bool) {
+	if tmpl != nil {
+		if fn := tmpl.funcs[name]; fn.IsValid() {
+			return fn, true
+		}
+	}
+	if set != nil {
+		if fn := set.funcs[name]; fn.IsValid() {
+			return fn, true
+		}
+	}
+	if fn := funcs[name]; fn.IsValid() {
+		return fn, true
+	}
+	return reflect.Value{}, false
+}
diff --git a/src/pkg/exp/template/parse.go b/src/pkg/exp/template/parse.go
index 74b5f2c0ae..aaed411d49 100644
--- a/src/pkg/exp/template/parse.go
+++ b/src/pkg/exp/template/parse.go
@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"os"
+	"reflect"
 	"runtime"
 	"strconv"
 	"strings"
@@ -16,8 +17,9 @@ import (
 
 // Template is the representation of a parsed template.
 type Template struct {
-	name string
-	root *listNode
+	name  string
+	root  *listNode
+	funcs map[string]reflect.Value
 	// Parsing.
 	lex      *lexer
 	tokens   <-chan item
@@ -450,12 +452,23 @@ func (w *withNode) String() string {
 // New allocates a new template with the given name.
 func New(name string) *Template {
 	return &Template{
-		name: name,
+		name:  name,
+		funcs: make(map[string]reflect.Value),
 	}
 }
 
+// Funcs adds to the template's function map the elements of the
+// argument map.   It panics if a value in the map is not a function
+// with appropriate return type.
+// The return value is the template, so calls can be chained.
+func (t *Template) Funcs(funcMap FuncMap) *Template {
+	addFuncs(t.funcs, funcMap)
+	return t
+}
+
 // errorf formats the error and terminates processing.
 func (t *Template) errorf(format string, args ...interface{}) {
+	t.root = nil
 	format = fmt.Sprintf("template: %s:%d: %s", t.name, t.lex.lineNumber(), format)
 	panic(fmt.Errorf(format, args...))
 }
@@ -488,7 +501,6 @@ func (t *Template) recover(errp *os.Error) {
 			panic(e)
 		}
 		t.stopParse()
-		t.root = nil
 		*errp = e.(os.Error)
 	}
 	return
diff --git a/src/pkg/exp/template/set.go b/src/pkg/exp/template/set.go
index 13d93d03ca..3aaabaad5a 100644
--- a/src/pkg/exp/template/set.go
+++ b/src/pkg/exp/template/set.go
@@ -6,6 +6,7 @@ package template
 
 import (
 	"os"
+	"reflect"
 	"runtime"
 	"strconv"
 )
@@ -13,16 +14,27 @@ import (
 // Set holds a set of related templates that can refer to one another by name.
 // A template may be a member of multiple sets.
 type Set struct {
-	tmpl map[string]*Template
+	tmpl  map[string]*Template
+	funcs map[string]reflect.Value
 }
 
 // NewSet allocates a new, empty template set.
 func NewSet() *Set {
 	return &Set{
-		tmpl: make(map[string]*Template),
+		tmpl:  make(map[string]*Template),
+		funcs: make(map[string]reflect.Value),
 	}
 }
 
+// Funcs adds to the set's function map the elements of the
+// argument map.   It panics if a value in the map is not a function
+// with appropriate return type.
+// The return value is the set, so calls can be chained.
+func (s *Set) Funcs(funcMap FuncMap) *Set {
+	addFuncs(s.funcs, funcMap)
+	return s
+}
+
 // recover is the handler that turns panics into returns from the top
 // level of Parse.
 func (s *Set) recover(errp *os.Error) {