exp/template: index function for arrays, slices, and maps.

R=golang-dev, adg, r
CC=golang-dev
https://golang.org/cl/4643072

src/pkg/exp/template/exec_test.go

@@ -31,6 +31,7 @@ type T struct {
 	MSI      map[string]int
 	MSIone   map[string]int // one element, for deterministic output
 	MSIEmpty map[string]int
+	SMSI     []map[string]int
 	// Empty interface; used to see if we can dig inside one.
 	EmptyInterface interface{}
 }
@@ -81,14 +82,18 @@ type U struct {
 }
 
 var tVal = &T{
-	I:              17,
-	U16:            16,
-	X:              "x",
-	U:              &U{"v"},
-	SI:             []int{3, 4, 5},
-	SB:             []bool{true, false},
-	MSI:            map[string]int{"one": 1, "two": 2, "three": 3},
-	MSIone:         map[string]int{"one": 1},
+	I:      17,
+	U16:    16,
+	X:      "x",
+	U:      &U{"v"},
+	SI:     []int{3, 4, 5},
+	SB:     []bool{true, false},
+	MSI:    map[string]int{"one": 1, "two": 2, "three": 3},
+	MSIone: map[string]int{"one": 1},
+	SMSI: []map[string]int{
+		{"one": 1, "two": 2},
+		{"eleven": 11, "twelve": 12},
+	},
 	EmptyInterface: []int{7, 8},
 }
 
@@ -166,6 +171,16 @@ var execTests = []execTest{
 	{"or", "{{or 0 0}} {{or 1 0}} {{or 0 1}} {{or 1 1}}", "false true true true", nil, true},
 	{"boolean if", "{{if and true 1 `hi`}}TRUE{{else}}FALSE{{end}}", "TRUE", tVal, true},
 	{"boolean if not", "{{if and true 1 `hi` | not}}TRUE{{else}}FALSE{{end}}", "FALSE", nil, true},
+	// Indexing.
+	{"slice[0]", "{{index .SI 0}}", "3", tVal, true},
+	{"slice[1]", "{{index .SI 1}}", "4", tVal, true},
+	{"slice[HUGE]", "{{index .SI 10}}", "", tVal, false},
+	{"slice[WRONG]", "{{index .SI `hello`}}", "", tVal, false},
+	{"map[one]", "{{index .MSI `one`}}", "1", tVal, true},
+	{"map[two]", "{{index .MSI `two`}}", "2", tVal, true},
+	{"map[NO]", "{{index .MSI `XXX`}}", "", tVal, false},
+	{"map[WRONG]", "{{index .MSI 10}}", "", tVal, false},
+	{"double index", "{{index .SMSI 1 `eleven`}}", "11", tVal, true},
 	// With.
 	{"with true", "{{with true}}{{.}}{{end}}", "true", tVal, true},
 	{"with false", "{{with false}}{{.}}{{else}}FALSE{{end}}", "FALSE", tVal, true},
@@ -222,7 +237,10 @@ func testExecute(execTests []execTest, set *Set, t *testing.T) {
 			t.Errorf("%s: unexpected execute error: %s", test.name, err)
 			continue
 		case !test.ok && err != nil:
-			continue
+			// expected error, got one
+			if *debug {
+				fmt.Printf("%s: %s\n\t%s\n", test.name, test.input, err)
+			}
 		}
 		result := b.String()
 		if result != test.output {

src/pkg/exp/template/funcs.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"os"
 	"reflect"
 	"strings"
 	"unicode"
@@ -20,12 +21,13 @@ import (
 type FuncMap map[string]interface{}
 
 var funcs = map[string]reflect.Value{
-	"printf": reflect.ValueOf(fmt.Sprintf),
+	"and":    reflect.ValueOf(and),
 	"html":   reflect.ValueOf(HTMLEscaper),
+	"index":  reflect.ValueOf(index),
 	"js":     reflect.ValueOf(JSEscaper),
-	"and":    reflect.ValueOf(and),
-	"or":     reflect.ValueOf(or),
 	"not":    reflect.ValueOf(not),
+	"or":     reflect.ValueOf(or),
+	"printf": reflect.ValueOf(fmt.Sprintf),
 }
 
 // addFuncs adds to values the functions in funcs, converting them to reflect.Values.
@@ -72,6 +74,45 @@ func findFunction(name string, tmpl *Template, set *Set) (reflect.Value, bool) {
 	return reflect.Value{}, false
 }
 
+// Indexing.
+
+// index returns the result of indexing its first argument by the following
+// arguments.  Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
+// indexed item must be a map, slice, or array.
+func index(item interface{}, indices ...interface{}) (interface{}, os.Error) {
+	v := reflect.ValueOf(item)
+	for _, i := range indices {
+		index := reflect.ValueOf(i)
+		switch v.Kind() {
+		case reflect.Array, reflect.Slice:
+			var x int64
+			switch index.Kind() {
+			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+				x = index.Int()
+			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+				x = int64(index.Uint())
+			default:
+				return nil, fmt.Errorf("cannot index slice/array with type %s", index.Type())
+			}
+			if x < 0 || x >= int64(v.Len()) {
+				return nil, fmt.Errorf("index out of range: %d", x)
+			}
+			v = v.Index(int(x))
+		case reflect.Map:
+			if !index.Type().AssignableTo(v.Type().Key()) {
+				return nil, fmt.Errorf("%s is not index type for %s", index.Type(), v.Type())
+			}
+			v = v.MapIndex(index)
+			if !v.IsValid() {
+				return nil, fmt.Errorf("index %v not present in map", index.Interface())
+			}
+		default:
+			return nil, fmt.Errorf("can't index item of type %s", index.Type())
+		}
+	}
+	return v.Interface(), nil
+}
+
 // Boolean logic.
 
 // and returns the Boolean AND of its arguments.