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funcs.go
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funcs.go
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package texttemplate
import (
"fmt"
"reflect"
"sync"
"unicode"
)
type FuncMap map[string]any
// builtins returns the FuncMap.
// It is not a global variable so the linker can dead code eliminate
// more when this isn't called. See golang.org/issue/36021.
// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
func builtins() FuncMap {
return FuncMap{
"print": fmt.Sprint,
"printf": fmt.Sprintf,
"println": fmt.Sprintln,
"not": not,
}
}
var builtinFuncsOnce struct {
sync.Once
v map[string]reflect.Value
}
// builtinFuncsOnce lazily computes & caches the builtinFuncs map.
// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
func builtinFuncs() map[string]reflect.Value {
builtinFuncsOnce.Do(func() {
builtinFuncsOnce.v = createValueFuncs(builtins())
})
return builtinFuncsOnce.v
}
// createValueFuncs turns a FuncMap into a map[string]reflect.Value
func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
m := make(map[string]reflect.Value)
addValueFuncs(m, funcMap)
return m
}
// addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
for name, fn := range in {
if !goodName(name) {
panic(fmt.Errorf("function name %q is not a valid identifier", name))
}
v := reflect.ValueOf(fn)
if v.Kind() != reflect.Func {
panic("value for " + name + " not a function")
}
if !goodFunc(v.Type()) {
panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut()))
}
out[name] = v
}
}
// goodFunc reports whether the function or method has the right result signature.
func goodFunc(typ reflect.Type) bool {
// We allow functions with 1 result or 2 results where the second is an error.
switch {
case typ.NumOut() == 1:
return true
case typ.NumOut() == 2 && typ.Out(1) == errorType:
return true
}
return false
}
// goodName reports whether the function name is a valid identifier.
func goodName(name string) bool {
if name == "" {
return false
}
for i, r := range name {
switch {
case r == '_':
case i == 0 && !unicode.IsLetter(r):
return false
case !unicode.IsLetter(r) && !unicode.IsDigit(r):
return false
}
}
return true
}
// findFunction looks for a function in the template, and global map.
func findFunction(name string, tmpl *Template) (v reflect.Value, isBuiltin, ok bool) {
if tmpl != nil && tmpl.common != nil {
tmpl.muFuncs.RLock()
defer tmpl.muFuncs.RUnlock()
if fn := tmpl.execFuncs[name]; fn.IsValid() {
return fn, false, true
}
}
if fn := builtinFuncs()[name]; fn.IsValid() {
return fn, true, true
}
return reflect.Value{}, false, false
}
func truth(arg reflect.Value) bool {
t, _ := isTrue(indirectInterface(arg))
return t
}
// safeCall runs fun.Call(args), and returns the resulting value and error, if
// any. If the call panics, the panic value is returned as an error.
func safeCall(fun reflect.Value, args []reflect.Value) (val reflect.Value, err error) {
defer func() {
if r := recover(); r != nil {
if e, ok := r.(error); ok {
err = e
} else {
err = fmt.Errorf("%v", r)
}
}
}()
ret := fun.Call(args)
if len(ret) == 2 && !ret[1].IsNil() {
return ret[0], ret[1].Interface().(error)
}
return ret[0], nil
}
// not returns the Boolean negation of its argument.
func not(arg reflect.Value) bool {
return !truth(arg)
}