exp/template: make numbers adhere to Go's rules for ideal constants.

Without further type informatnion, 1.0 is a float and an integer
must fit in an int.

R=rsc
CC=golang-dev
https://golang.org/cl/4696042

src/pkg/exp/template/exec.go

@@ -300,19 +300,7 @@ func (s *state) evalCommand(dot reflect.Value, cmd *commandNode, final reflect.V
 	case *dotNode:
 		return dot
 	case *numberNode:
-		// These are ideal constants but we don't know the type
-		// and we have no context.  (If it was a method argument,
-		// we'd know what we need.) The syntax guides us to some extent.
-		switch {
-		case word.isComplex:
-			return reflect.ValueOf(word.complex128) // incontrovertible.
-		case word.isFloat && strings.IndexAny(word.text, ".eE") >= 0:
-			return reflect.ValueOf(word.float64)
-		case word.isInt:
-			return reflect.ValueOf(word.int64)
-		case word.isUint:
-			return reflect.ValueOf(word.uint64)
-		}
+		return s.idealConstant(word)
 	case *stringNode:
 		return reflect.ValueOf(word.text)
 	}
@@ -320,6 +308,31 @@ func (s *state) evalCommand(dot reflect.Value, cmd *commandNode, final reflect.V
 	panic("not reached")
 }
 
+// idealConstant is called to return the value of a number in a context where
+// we don't know the type. In that case, the syntax of the number tells us
+// its type, and we use Go rules to resolve.  Note there is no such thing as
+// a uint ideal constant in this situation - the value must be of int type.
+func (s *state) idealConstant(constant *numberNode) reflect.Value {
+	// These are ideal constants but we don't know the type
+	// and we have no context.  (If it was a method argument,
+	// we'd know what we need.) The syntax guides us to some extent.
+	switch {
+	case constant.isComplex:
+		return reflect.ValueOf(constant.complex128) // incontrovertible.
+	case constant.isFloat && strings.IndexAny(constant.text, ".eE") >= 0:
+		return reflect.ValueOf(constant.float64)
+	case constant.isInt:
+		n := int(constant.int64)
+		if int64(n) != constant.int64 {
+			s.errorf("%s overflows int", constant.text)
+		}
+		return reflect.ValueOf(n)
+	case constant.isUint:
+		s.errorf("%s overflows int", constant.text)
+	}
+	return zero
+}
+
 func (s *state) evalFieldNode(dot reflect.Value, field *fieldNode, args []node, final reflect.Value) reflect.Value {
 	return s.evalFieldChain(dot, dot, field.ident, args, final)
 }
@@ -577,18 +590,7 @@ func (s *state) evalEmptyInterface(dot reflect.Value, n node) reflect.Value {
 	case *identifierNode:
 		return s.evalFunction(dot, n.ident, nil, zero)
 	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)
-		}
+		return s.idealConstant(n)
 	case *stringNode:
 		return reflect.ValueOf(n.text)
 	case *variableNode:

src/pkg/exp/template/exec_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"os"
+	"reflect"
 	"sort"
 	"strings"
 	"testing"
@@ -127,6 +128,10 @@ func (t *T) EPERM(error bool) (bool, os.Error) {
 	return false, nil
 }
 
+func typeOf(arg interface{}) string {
+	return fmt.Sprintf("%T", arg)
+}
+
 type execTest struct {
 	name   string
 	input  string
@@ -135,11 +140,27 @@ type execTest struct {
 	ok     bool
 }
 
+// bigInt and bigUint are hex string representing numbers either side
+// of the max int boundary.
+// We do it this way so the test doesn't depend on ints being 32 bits.
+var (
+	bigInt  = fmt.Sprintf("0x%x", int(1<<uint(reflect.TypeOf(0).Bits()-1)-1))
+	bigUint = fmt.Sprintf("0x%x", uint(1<<uint(reflect.TypeOf(0).Bits()-1)))
+)
+
 var execTests = []execTest{
 	// Trivial cases.
 	{"empty", "", "", nil, true},
 	{"text", "some text", "some text", nil, true},
 
+	// Ideal constants.
+	{"ideal int", "{{typeOf 3}}", "int", 0, true},
+	{"ideal float", "{{typeOf 1.0}}", "float64", 0, true},
+	{"ideal exp float", "{{typeOf 1e1}}", "float64", 0, true},
+	{"ideal complex", "{{typeOf 1i}}", "complex128", 0, true},
+	{"ideal int", "{{typeOf " + bigInt + "}}", "int", 0, true},
+	{"ideal too big", "{{typeOf " + bigUint + "}}", "", 0, false},
+
 	// Fields of structs.
 	{".X", "-{{.X}}-", "-x-", tVal, true},
 	{".U.V", "-{{.U.V}}-", "-v-", tVal, true},
@@ -301,7 +322,7 @@ func oneArg(a string) string {
 
 func testExecute(execTests []execTest, set *Set, t *testing.T) {
 	b := new(bytes.Buffer)
-	funcs := FuncMap{"zeroArgs": zeroArgs, "oneArg": oneArg}
+	funcs := FuncMap{"zeroArgs": zeroArgs, "oneArg": oneArg, "typeOf": typeOf}
 	for _, test := range execTests {
 		tmpl := New(test.name).Funcs(funcs)
 		err := tmpl.Parse(test.input)