statsd_exporter/vendor/github.com/alecthomas/template/template.go
2017-08-30 17:48:19 +02:00

218 lines
6.6 KiB
Go

// 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"
"github.com/alecthomas/template/parse"
)
// common holds the information shared by related templates.
type common struct {
tmpl map[string]*Template
// We use two maps, one for parsing and one for execution.
// This separation makes the API cleaner since it doesn't
// expose reflection to the client.
parseFuncs FuncMap
execFuncs map[string]reflect.Value
}
// Template is the representation of a parsed template. The *parse.Tree
// field is exported only for use by html/template and should be treated
// as unexported by all other clients.
type Template struct {
name string
*parse.Tree
*common
leftDelim string
rightDelim string
}
// New allocates a new template with the given name.
func New(name string) *Template {
return &Template{
name: name,
}
}
// Name returns the name of the template.
func (t *Template) Name() string {
return t.name
}
// New allocates a new template associated with the given one and with the same
// delimiters. The association, which is transitive, allows one template to
// invoke another with a {{template}} action.
func (t *Template) New(name string) *Template {
t.init()
return &Template{
name: name,
common: t.common,
leftDelim: t.leftDelim,
rightDelim: t.rightDelim,
}
}
func (t *Template) init() {
if t.common == nil {
t.common = new(common)
t.tmpl = make(map[string]*Template)
t.parseFuncs = make(FuncMap)
t.execFuncs = make(map[string]reflect.Value)
}
}
// Clone returns a duplicate of the template, including all associated
// templates. The actual representation is not copied, but the name space of
// associated templates is, so further calls to Parse in the copy will add
// templates to the copy but not to the original. Clone can be used to prepare
// common templates and use them with variant definitions for other templates
// by adding the variants after the clone is made.
func (t *Template) Clone() (*Template, error) {
nt := t.copy(nil)
nt.init()
nt.tmpl[t.name] = nt
for k, v := range t.tmpl {
if k == t.name { // Already installed.
continue
}
// The associated templates share nt's common structure.
tmpl := v.copy(nt.common)
nt.tmpl[k] = tmpl
}
for k, v := range t.parseFuncs {
nt.parseFuncs[k] = v
}
for k, v := range t.execFuncs {
nt.execFuncs[k] = v
}
return nt, nil
}
// copy returns a shallow copy of t, with common set to the argument.
func (t *Template) copy(c *common) *Template {
nt := New(t.name)
nt.Tree = t.Tree
nt.common = c
nt.leftDelim = t.leftDelim
nt.rightDelim = t.rightDelim
return nt
}
// AddParseTree creates a new template with the name and parse tree
// and associates it with t.
func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
if t.common != nil && t.tmpl[name] != nil {
return nil, fmt.Errorf("template: redefinition of template %q", name)
}
nt := t.New(name)
nt.Tree = tree
t.tmpl[name] = nt
return nt, nil
}
// Templates returns a slice of the templates associated with t, including t
// itself.
func (t *Template) Templates() []*Template {
if t.common == nil {
return nil
}
// Return a slice so we don't expose the map.
m := make([]*Template, 0, len(t.tmpl))
for _, v := range t.tmpl {
m = append(m, v)
}
return m
}
// Delims sets the action delimiters to the specified strings, to be used in
// subsequent calls to Parse, ParseFiles, or ParseGlob. Nested template
// definitions will inherit the settings. An empty delimiter stands for the
// corresponding default: {{ or }}.
// The return value is the template, so calls can be chained.
func (t *Template) Delims(left, right string) *Template {
t.leftDelim = left
t.rightDelim = right
return t
}
// Funcs adds the elements of the argument map to the template's function map.
// It panics if a value in the map is not a function with appropriate return
// type. However, it is legal to overwrite elements of the map. The return
// value is the template, so calls can be chained.
func (t *Template) Funcs(funcMap FuncMap) *Template {
t.init()
addValueFuncs(t.execFuncs, funcMap)
addFuncs(t.parseFuncs, funcMap)
return t
}
// Lookup returns the template with the given name that is associated with t,
// or nil if there is no such template.
func (t *Template) Lookup(name string) *Template {
if t.common == nil {
return nil
}
return t.tmpl[name]
}
// Parse parses a string into a template. Nested template definitions will be
// associated with the top-level template t. Parse may be called multiple times
// to parse definitions of templates to associate with t. It is an error if a
// resulting template is non-empty (contains content other than template
// definitions) and would replace a non-empty template with the same name.
// (In multiple calls to Parse with the same receiver template, only one call
// can contain text other than space, comments, and template definitions.)
func (t *Template) Parse(text string) (*Template, error) {
t.init()
trees, err := parse.Parse(t.name, text, t.leftDelim, t.rightDelim, t.parseFuncs, builtins)
if err != nil {
return nil, err
}
// Add the newly parsed trees, including the one for t, into our common structure.
for name, tree := range trees {
// If the name we parsed is the name of this template, overwrite this template.
// The associate method checks it's not a redefinition.
tmpl := t
if name != t.name {
tmpl = t.New(name)
}
// Even if t == tmpl, we need to install it in the common.tmpl map.
if replace, err := t.associate(tmpl, tree); err != nil {
return nil, err
} else if replace {
tmpl.Tree = tree
}
tmpl.leftDelim = t.leftDelim
tmpl.rightDelim = t.rightDelim
}
return t, nil
}
// associate installs the new template into the group of templates associated
// with t. It is an error to reuse a name except to overwrite an empty
// template. The two are already known to share the common structure.
// The boolean return value reports wither to store this tree as t.Tree.
func (t *Template) associate(new *Template, tree *parse.Tree) (bool, error) {
if new.common != t.common {
panic("internal error: associate not common")
}
name := new.name
if old := t.tmpl[name]; old != nil {
oldIsEmpty := parse.IsEmptyTree(old.Root)
newIsEmpty := parse.IsEmptyTree(tree.Root)
if newIsEmpty {
// Whether old is empty or not, new is empty; no reason to replace old.
return false, nil
}
if !oldIsEmpty {
return false, fmt.Errorf("template: redefinition of template %q", name)
}
}
t.tmpl[name] = new
return true, nil
}