CODEWITHSUNDEEP
gogo-templates
Evan Plumlee
Evan Plumlee

Reputation: 325

text/template issue Parse() vs. ParseFiles()

I'm trying to do some simple work with the text/template package. The sample given at the top of template is what I'm working with.

How do I write the 'parsed' file so template.ParseFiles() properly reads and executes it?

package main

import (
    "text/template"
    "os"
)

type Inventory struct {
    Material string
    Count    uint
}

func main() {
    sweaters := Inventory{"wool", 17}
    tmpl, err := template.New("test").Parse("{{.Count}} items are made of {{.Material}}")
    // tmpl, err := template.New("test").ParseFiles("file.txt")

    if err != nil { panic(err) }
    err = tmpl.Execute(os.Stdout, sweaters)
    if err != nil { panic(err) }
}

/*
Contents of file.txt:
{{.Count}} items are made of {{.Material}}

Error thrown:
panic: template: test:1: "test" is an incomplete or empty template

goroutine 1 [running]:
main.main()
    /tmp/templates/t.go:19 +0x21a

goroutine 2 [syscall]:
created by runtime.main
    /var/tmp/portage/dev-lang/go-1.0.1/work/go/src/pkg/runtime/proc.c:221
*/

I have a copy of this code posted at the golang playground here

Edit #1: I've been doing some research on this issue... since it's the Execute() method that actually throws the exception, and not the ParseFiles() part, I checked the method definition:

// Execute applies a parsed template to the specified data object,
// and writes the output to wr.
func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
    defer errRecover(&err)
    value := reflect.ValueOf(data)
    state := &state{
        tmpl: t,
        wr:   wr,
        line: 1,
        vars: []variable{{"$", value}},
    }
    if t.Tree == nil || t.Root == nil {
        state.errorf("%q is an incomplete or empty template", t.name)
    }
    state.walk(value, t.Root)
    return
}

So, on a hunch, I dumped the value of t.Tree for the inline 'non-file' style, tmpl is: &parse.Tree{Name:"test", Root:(*parse.ListNode)(0xf840030700), funcs:[]map[string]interface {}(nil), lex:(*parse.lexer)(nil), token:[2]parse.item{parse.item{typ:6, val:""}, parse.item{typ:9, val:"{{"}}, peekCount:1, vars:[]string(nil)} and when ran with ParseFiles(), tmpl is: (*parse.Tree)(nil). I find it odd that one is a dereference, and one value is a pointer. This may help solve the riddle

Upvotes: 6

Views: 22992

Answers (2)

jolestar
jolestar

Reputation: 1333

There is a little trick in Go template parseFiles.

func parseFiles(t *Template, filenames ...string) (*Template, error) {
    if len(filenames) == 0 {
        // Not really a problem, but be consistent.
        return nil, fmt.Errorf("template: no files named in call to ParseFiles")
    }
    for _, filename := range filenames {
        b, err := ioutil.ReadFile(filename)
        if err != nil {
            return nil, err
        }
        s := string(b)
        name := filepath.Base(filename)
        // First template becomes return value if not already defined,
        // and we use that one for subsequent New calls to associate
        // all the templates together. Also, if this file has the same name
        // as t, this file becomes the contents of t, so
        //  t, err := New(name).Funcs(xxx).ParseFiles(name)
        // works. Otherwise we create a new template associated with t.
        var tmpl *Template
        if t == nil {
            t = New(name)
        }
        if name == t.Name() {
            tmpl = t
        } else {
            tmpl = t.New(name)
        }
        _, err = tmpl.Parse(s)
        if err != nil {
            return nil, err
        }
    }
    return t, nil
}

Only the template with same name will be reuse, otherwise create new one. as your sample:

tmpl, err := template.New("test").ParseFiles("file.txt")

tmpl is the template named "test", and associated another template named "file.txt", you call Execute on "test" template, this template is a empty template, so raise the error "test is an incomplete or empty template".

It worked when you change the template name to file.txt

tmpl, err := template.New("file.txt").ParseFiles("file.txt")

Upvotes: 11

Eli Revah
Eli Revah

Reputation: 3676

sweaters := Inventory{"wool", 17}
tmpl, err := template.ParseFiles("file.txt")
if err != nil {
    panic(err)
}
err = tmpl.ExecuteTemplate(os.Stdout, "file.txt", sweaters)
if err != nil {
    panic(err)
}

If you have many files, you can use ParseGlob:

tmpl, err := template.ParseGlob("*.txt")
if err != nil {
    panic(err)
}
err = tmpl.ExecuteTemplate(os.Stdout, "file.txt", sweaters)
if err != nil {
    panic(err)
}
err = tmpl.ExecuteTemplate(os.Stdout, "file2.txt", sweaters)
if err != nil {
    panic(err)
}

Upvotes: 17

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