text/template: Call using complex128 as type string

[dvyukov]

The following program crashes with a panic:

package main

import (
    "errors"
    "text/template"
    "io/ioutil"
)

func main() {
    data := "{{0i|printf}}"
    t, err := template.New("foo").Funcs(funcs).Parse(string(data))
    if err != nil {
        if t != nil {
            panic("non nil template on error")
        }
        return
    }
    d := &Data{
        A: 42,
        B: "foo",
        C: []int{1, 2, 3},
        D: map[int]string{1: "foo", 2: "bar"},
        E: Data1{42, "foo"},
    }
    t.Execute(ioutil.Discard, d)
    return
}

type Data struct {
    A int
    B string
    C []int
    D map[int]string
    E Data1
}

type Data1 struct {
    A int
    B string
}

func (Data1) Q() string {
    return "foo"
}

func (Data1) W() (string, error) {
    return "foo", nil
}

func (Data1) E() (string, error) {
    return "foo", errors.New("Data.E error")
}

func (Data1) R(v int) (string, error) {
    return "foo", nil
}

func (Data1) T(s string) (string, error) {
    return s, nil
}

var funcs = map[string]interface{}{
    "Q": func1,
    "W": func2,
    "E": func3,
    "R": func4,
    "T": func5,
    "Y": func6,
    "U": func7,
    "I": func8,
}

func func1(s string) string {
    return s
}

func func2(s string) (string, error) {
    return s, nil
}

func func3(s string) (string, error) {
    return s, errors.New("func3 error")
}

func func4(v int) int {
    return v
}

func func5(v int) (int, error) {
    return v, nil
}

func func6() int {
    return 42
}

func func7() (int, error) {
    return 42, nil
}

func func8() (int, error) {
    return 42, errors.New("func8 error")
}

panic: reflect: Call using complex128 as type string [recovered]
    panic: reflect: Call using complex128 as type string

goroutine 1 [running]:
text/template.errRecover(0xc208041ee8)
    src/text/template/exec.go:104 +0x146
reflect.Value.call(0x52db60, 0x5bbe98, 0x13, 0x56c8f0, 0x4, 0xc20800e440, 0x1, 0x1, 0x0, 0x0, ...)
    src/reflect/value.go:369 +0x74d
reflect.Value.Call(0x52db60, 0x5bbe98, 0x13, 0xc20800e440, 0x1, 0x1, 0x0, 0x0, 0x0)
    src/reflect/value.go:300 +0xb4
text/template.(*state).evalCall(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0x52db60, 0x5bbe98, 0x13, 0x7f702f59a350, 0xc2080145a0, 0x5828d5, ...)
    src/text/template/exec.go:592 +0xb04
text/template.(*state).evalFunction(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0xc2080145d0, 0x7f702f59a350, 0xc2080145a0, 0xc20800a500, 0x1, 0x1, ...)
    src/text/template/exec.go:473 +0x340
text/template.(*state).evalCommand(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0xc2080145a0, 0x505840, 0xc20800a520, 0x50, 0x0, 0x0, ...)
    src/text/template/exec.go:370 +0x1ec
text/template.(*state).evalPipeline(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0xc2080121e0, 0x505840, 0xc20800a520, 0x50)
    src/text/template/exec.go:343 +0x183
text/template.(*state).walk(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0x7f702f59a278, 0xc208014600)
    src/text/template/exec.go:178 +0x138
text/template.(*state).walk(0xc208041e78, 0x4f8500, 0xc208012230, 0x16, 0x7f702f59a2c0, 0xc208014540)
    src/text/template/exec.go:186 +0x779
text/template.(*Template).Execute(0xc208010440, 0x7f702f59a1c0, 0xc20800a490, 0x4f8500, 0xc208012230, 0x0, 0x0)
    src/text/template/exec.go:141 +0x406
main.main()
    template.go:25 +0x35d

on commit 8017ace

[dspezia]

It is unrelated to complex numbers. It fails in the same way with any value which is not a string, such as:

 {{true | printf}}
 {{1|printf}}
 {{1.1|printf}}
 {{'x'|printf}}

I think it is due to a unmanaged corner case involving variadic functions featuring a []interface{} slice.
Working on a fix.

[gopherbot]

CL https://golang.org/cl/10403 mentions this issue.