// 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. // Helper functions to make constructing templates easier. package template import ( "fmt" "io/fs" "os" "path" "path/filepath" ) // Functions and methods to parse templates. // Must is a helper that wraps a call to a function returning (*Template, error) // and panics if the error is non-nil. It is intended for use in variable // initializations such as // var t = template.Must(template.New("name").Parse("text")) func Must(t *Template, err error) *Template { if err != nil { panic(err) } return t } // ParseFiles creates a new Template and parses the template definitions from // the named files. The returned template's name will have the base name and // parsed contents of the first file. There must be at least one file. // If an error occurs, parsing stops and the returned *Template is nil. // // When parsing multiple files with the same name in different directories, // the last one mentioned will be the one that results. // For instance, ParseFiles("a/foo", "b/foo") stores "b/foo" as the template // named "foo", while "a/foo" is unavailable. func ParseFiles(filenames ...string) (*Template, error) { return parseFiles(nil, readFileOS, filenames...) } // ParseFiles parses the named files and associates the resulting templates with // t. If an error occurs, parsing stops and the returned template is nil; // otherwise it is t. There must be at least one file. // Since the templates created by ParseFiles are named by the base // names of the argument files, t should usually have the name of one // of the (base) names of the files. If it does not, depending on t's // contents before calling ParseFiles, t.Execute may fail. In that // case use t.ExecuteTemplate to execute a valid template. // // When parsing multiple files with the same name in different directories, // the last one mentioned will be the one that results. func (t *Template) ParseFiles(filenames ...string) (*Template, error) { t.init() return parseFiles(t, readFileOS, filenames...) } // parseFiles is the helper for the method and function. If the argument // template is nil, it is created from the first file. func parseFiles(t *Template, readFile func(string) (string, []byte, error), 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 { name, b, err := readFile(filename) if err != nil { return nil, err } s := string(b) // 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 } // ParseGlob creates a new Template and parses the template definitions from // the files identified by the pattern. The files are matched according to the // semantics of filepath.Match, and the pattern must match at least one file. // The returned template will have the (base) name and (parsed) contents of the // first file matched by the pattern. ParseGlob is equivalent to calling // ParseFiles with the list of files matched by the pattern. // // When parsing multiple files with the same name in different directories, // the last one mentioned will be the one that results. func ParseGlob(pattern string) (*Template, error) { return parseGlob(nil, pattern) } // ParseGlob parses the template definitions in the files identified by the // pattern and associates the resulting templates with t. The files are matched // according to the semantics of filepath.Match, and the pattern must match at // least one file. ParseGlob is equivalent to calling t.ParseFiles with the // list of files matched by the pattern. // // When parsing multiple files with the same name in different directories, // the last one mentioned will be the one that results. func (t *Template) ParseGlob(pattern string) (*Template, error) { t.init() return parseGlob(t, pattern) } // parseGlob is the implementation of the function and method ParseGlob. func parseGlob(t *Template, pattern string) (*Template, error) { filenames, err := filepath.Glob(pattern) if err != nil { return nil, err } if len(filenames) == 0 { return nil, fmt.Errorf("template: pattern matches no files: %#q", pattern) } return parseFiles(t, readFileOS, filenames...) } // ParseFS is like ParseFiles or ParseGlob but reads from the file system fsys // instead of the host operating system's file system. // It accepts a list of glob patterns. // (Note that most file names serve as glob patterns matching only themselves.) func ParseFS(fsys fs.FS, patterns ...string) (*Template, error) { return parseFS(nil, fsys, patterns) } // ParseFS is like ParseFiles or ParseGlob but reads from the file system fsys // instead of the host operating system's file system. // It accepts a list of glob patterns. // (Note that most file names serve as glob patterns matching only themselves.) func (t *Template) ParseFS(fsys fs.FS, patterns ...string) (*Template, error) { t.init() return parseFS(t, fsys, patterns) } func parseFS(t *Template, fsys fs.FS, patterns []string) (*Template, error) { var filenames []string for _, pattern := range patterns { list, err := fs.Glob(fsys, pattern) if err != nil { return nil, err } if len(list) == 0 { return nil, fmt.Errorf("template: pattern matches no files: %#q", pattern) } filenames = append(filenames, list...) } return parseFiles(t, readFileFS(fsys), filenames...) } func readFileOS(file string) (name string, b []byte, err error) { name = filepath.Base(file) b, err = os.ReadFile(file) return } func readFileFS(fsys fs.FS) func(string) (string, []byte, error) { return func(file string) (name string, b []byte, err error) { name = path.Base(file) b, err = fs.ReadFile(fsys, file) return } }