Source file src/html/template/examplefiles_test.go

     1  // Copyright 2016 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package template_test
     6  
     7  import (
     8  	"io"
     9  	"log"
    10  	"os"
    11  	"path/filepath"
    12  	"text/template"
    13  )
    14  
    15  // templateFile defines the contents of a template to be stored in a file, for testing.
    16  type templateFile struct {
    17  	name     string
    18  	contents string
    19  }
    20  
    21  func createTestDir(files []templateFile) string {
    22  	dir, err := os.MkdirTemp("", "template")
    23  	if err != nil {
    24  		log.Fatal(err)
    25  	}
    26  	for _, file := range files {
    27  		f, err := os.Create(filepath.Join(dir, file.name))
    28  		if err != nil {
    29  			log.Fatal(err)
    30  		}
    31  		defer f.Close()
    32  		_, err = io.WriteString(f, file.contents)
    33  		if err != nil {
    34  			log.Fatal(err)
    35  		}
    36  	}
    37  	return dir
    38  }
    39  
    40  // The following example is duplicated in text/template; keep them in sync.
    41  
    42  // Here we demonstrate loading a set of templates from a directory.
    43  func ExampleTemplate_glob() {
    44  	// Here we create a temporary directory and populate it with our sample
    45  	// template definition files; usually the template files would already
    46  	// exist in some location known to the program.
    47  	dir := createTestDir([]templateFile{
    48  		// T0.tmpl is a plain template file that just invokes T1.
    49  		{"T0.tmpl", `T0 invokes T1: ({{template "T1"}})`},
    50  		// T1.tmpl defines a template, T1 that invokes T2.
    51  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
    52  		// T2.tmpl defines a template T2.
    53  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
    54  	})
    55  	// Clean up after the test; another quirk of running as an example.
    56  	defer os.RemoveAll(dir)
    57  
    58  	// pattern is the glob pattern used to find all the template files.
    59  	pattern := filepath.Join(dir, "*.tmpl")
    60  
    61  	// Here starts the example proper.
    62  	// T0.tmpl is the first name matched, so it becomes the starting template,
    63  	// the value returned by ParseGlob.
    64  	tmpl := template.Must(template.ParseGlob(pattern))
    65  
    66  	err := tmpl.Execute(os.Stdout, nil)
    67  	if err != nil {
    68  		log.Fatalf("template execution: %s", err)
    69  	}
    70  	// Output:
    71  	// T0 invokes T1: (T1 invokes T2: (This is T2))
    72  }
    73  
    74  // Here we demonstrate loading a set of templates from files in different directories
    75  func ExampleTemplate_parsefiles() {
    76  	// Here we create different temporary directories and populate them with our sample
    77  	// template definition files; usually the template files would already
    78  	// exist in some location known to the program.
    79  	dir1 := createTestDir([]templateFile{
    80  		// T1.tmpl is a plain template file that just invokes T2.
    81  		{"T1.tmpl", `T1 invokes T2: ({{template "T2"}})`},
    82  	})
    83  
    84  	dir2 := createTestDir([]templateFile{
    85  		// T2.tmpl defines a template T2.
    86  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
    87  	})
    88  
    89  	// Clean up after the test; another quirk of running as an example.
    90  	defer func(dirs ...string) {
    91  		for _, dir := range dirs {
    92  			os.RemoveAll(dir)
    93  		}
    94  	}(dir1, dir2)
    95  
    96  	// Here starts the example proper.
    97  	// Let's just parse only dir1/T0 and dir2/T2
    98  	paths := []string{
    99  		filepath.Join(dir1, "T1.tmpl"),
   100  		filepath.Join(dir2, "T2.tmpl"),
   101  	}
   102  	tmpl := template.Must(template.ParseFiles(paths...))
   103  
   104  	err := tmpl.Execute(os.Stdout, nil)
   105  	if err != nil {
   106  		log.Fatalf("template execution: %s", err)
   107  	}
   108  	// Output:
   109  	// T1 invokes T2: (This is T2)
   110  }
   111  
   112  // The following example is duplicated in text/template; keep them in sync.
   113  
   114  // This example demonstrates one way to share some templates
   115  // and use them in different contexts. In this variant we add multiple driver
   116  // templates by hand to an existing bundle of templates.
   117  func ExampleTemplate_helpers() {
   118  	// Here we create a temporary directory and populate it with our sample
   119  	// template definition files; usually the template files would already
   120  	// exist in some location known to the program.
   121  	dir := createTestDir([]templateFile{
   122  		// T1.tmpl defines a template, T1 that invokes T2.
   123  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
   124  		// T2.tmpl defines a template T2.
   125  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
   126  	})
   127  	// Clean up after the test; another quirk of running as an example.
   128  	defer os.RemoveAll(dir)
   129  
   130  	// pattern is the glob pattern used to find all the template files.
   131  	pattern := filepath.Join(dir, "*.tmpl")
   132  
   133  	// Here starts the example proper.
   134  	// Load the helpers.
   135  	templates := template.Must(template.ParseGlob(pattern))
   136  	// Add one driver template to the bunch; we do this with an explicit template definition.
   137  	_, err := templates.Parse("{{define `driver1`}}Driver 1 calls T1: ({{template `T1`}})\n{{end}}")
   138  	if err != nil {
   139  		log.Fatal("parsing driver1: ", err)
   140  	}
   141  	// Add another driver template.
   142  	_, err = templates.Parse("{{define `driver2`}}Driver 2 calls T2: ({{template `T2`}})\n{{end}}")
   143  	if err != nil {
   144  		log.Fatal("parsing driver2: ", err)
   145  	}
   146  	// We load all the templates before execution. This package does not require
   147  	// that behavior but html/template's escaping does, so it's a good habit.
   148  	err = templates.ExecuteTemplate(os.Stdout, "driver1", nil)
   149  	if err != nil {
   150  		log.Fatalf("driver1 execution: %s", err)
   151  	}
   152  	err = templates.ExecuteTemplate(os.Stdout, "driver2", nil)
   153  	if err != nil {
   154  		log.Fatalf("driver2 execution: %s", err)
   155  	}
   156  	// Output:
   157  	// Driver 1 calls T1: (T1 invokes T2: (This is T2))
   158  	// Driver 2 calls T2: (This is T2)
   159  }
   160  
   161  // The following example is duplicated in text/template; keep them in sync.
   162  
   163  // This example demonstrates how to use one group of driver
   164  // templates with distinct sets of helper templates.
   165  func ExampleTemplate_share() {
   166  	// Here we create a temporary directory and populate it with our sample
   167  	// template definition files; usually the template files would already
   168  	// exist in some location known to the program.
   169  	dir := createTestDir([]templateFile{
   170  		// T0.tmpl is a plain template file that just invokes T1.
   171  		{"T0.tmpl", "T0 ({{.}} version) invokes T1: ({{template `T1`}})\n"},
   172  		// T1.tmpl defines a template, T1 that invokes T2. Note T2 is not defined
   173  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
   174  	})
   175  	// Clean up after the test; another quirk of running as an example.
   176  	defer os.RemoveAll(dir)
   177  
   178  	// pattern is the glob pattern used to find all the template files.
   179  	pattern := filepath.Join(dir, "*.tmpl")
   180  
   181  	// Here starts the example proper.
   182  	// Load the drivers.
   183  	drivers := template.Must(template.ParseGlob(pattern))
   184  
   185  	// We must define an implementation of the T2 template. First we clone
   186  	// the drivers, then add a definition of T2 to the template name space.
   187  
   188  	// 1. Clone the helper set to create a new name space from which to run them.
   189  	first, err := drivers.Clone()
   190  	if err != nil {
   191  		log.Fatal("cloning helpers: ", err)
   192  	}
   193  	// 2. Define T2, version A, and parse it.
   194  	_, err = first.Parse("{{define `T2`}}T2, version A{{end}}")
   195  	if err != nil {
   196  		log.Fatal("parsing T2: ", err)
   197  	}
   198  
   199  	// Now repeat the whole thing, using a different version of T2.
   200  	// 1. Clone the drivers.
   201  	second, err := drivers.Clone()
   202  	if err != nil {
   203  		log.Fatal("cloning drivers: ", err)
   204  	}
   205  	// 2. Define T2, version B, and parse it.
   206  	_, err = second.Parse("{{define `T2`}}T2, version B{{end}}")
   207  	if err != nil {
   208  		log.Fatal("parsing T2: ", err)
   209  	}
   210  
   211  	// Execute the templates in the reverse order to verify the
   212  	// first is unaffected by the second.
   213  	err = second.ExecuteTemplate(os.Stdout, "T0.tmpl", "second")
   214  	if err != nil {
   215  		log.Fatalf("second execution: %s", err)
   216  	}
   217  	err = first.ExecuteTemplate(os.Stdout, "T0.tmpl", "first")
   218  	if err != nil {
   219  		log.Fatalf("first: execution: %s", err)
   220  	}
   221  
   222  	// Output:
   223  	// T0 (second version) invokes T1: (T1 invokes T2: (T2, version B))
   224  	// T0 (first version) invokes T1: (T1 invokes T2: (T2, version A))
   225  }
   226  

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