examplefiles_test.go

Documentation: text/template

		 1  // Copyright 2012 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  // Here we demonstrate loading a set of templates from a directory.
		41  func ExampleTemplate_glob() {
		42  	// Here we create a temporary directory and populate it with our sample
		43  	// template definition files; usually the template files would already
		44  	// exist in some location known to the program.
		45  	dir := createTestDir([]templateFile{
		46  		// T0.tmpl is a plain template file that just invokes T1.
		47  		{"T0.tmpl", `T0 invokes T1: ({{template "T1"}})`},
		48  		// T1.tmpl defines a template, T1 that invokes T2.
		49  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
		50  		// T2.tmpl defines a template T2.
		51  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
		52  	})
		53  	// Clean up after the test; another quirk of running as an example.
		54  	defer os.RemoveAll(dir)
		55  
		56  	// pattern is the glob pattern used to find all the template files.
		57  	pattern := filepath.Join(dir, "*.tmpl")
		58  
		59  	// Here starts the example proper.
		60  	// T0.tmpl is the first name matched, so it becomes the starting template,
		61  	// the value returned by ParseGlob.
		62  	tmpl := template.Must(template.ParseGlob(pattern))
		63  
		64  	err := tmpl.Execute(os.Stdout, nil)
		65  	if err != nil {
		66  		log.Fatalf("template execution: %s", err)
		67  	}
		68  	// Output:
		69  	// T0 invokes T1: (T1 invokes T2: (This is T2))
		70  }
		71  
		72  // This example demonstrates one way to share some templates
		73  // and use them in different contexts. In this variant we add multiple driver
		74  // templates by hand to an existing bundle of templates.
		75  func ExampleTemplate_helpers() {
		76  	// Here we create a temporary directory and populate it with our sample
		77  	// template definition files; usually the template files would already
		78  	// exist in some location known to the program.
		79  	dir := createTestDir([]templateFile{
		80  		// T1.tmpl defines a template, T1 that invokes T2.
		81  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
		82  		// T2.tmpl defines a template T2.
		83  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
		84  	})
		85  	// Clean up after the test; another quirk of running as an example.
		86  	defer os.RemoveAll(dir)
		87  
		88  	// pattern is the glob pattern used to find all the template files.
		89  	pattern := filepath.Join(dir, "*.tmpl")
		90  
		91  	// Here starts the example proper.
		92  	// Load the helpers.
		93  	templates := template.Must(template.ParseGlob(pattern))
		94  	// Add one driver template to the bunch; we do this with an explicit template definition.
		95  	_, err := templates.Parse("{{define `driver1`}}Driver 1 calls T1: ({{template `T1`}})\n{{end}}")
		96  	if err != nil {
		97  		log.Fatal("parsing driver1: ", err)
		98  	}
		99  	// Add another driver template.
	 100  	_, err = templates.Parse("{{define `driver2`}}Driver 2 calls T2: ({{template `T2`}})\n{{end}}")
	 101  	if err != nil {
	 102  		log.Fatal("parsing driver2: ", err)
	 103  	}
	 104  	// We load all the templates before execution. This package does not require
	 105  	// that behavior but html/template's escaping does, so it's a good habit.
	 106  	err = templates.ExecuteTemplate(os.Stdout, "driver1", nil)
	 107  	if err != nil {
	 108  		log.Fatalf("driver1 execution: %s", err)
	 109  	}
	 110  	err = templates.ExecuteTemplate(os.Stdout, "driver2", nil)
	 111  	if err != nil {
	 112  		log.Fatalf("driver2 execution: %s", err)
	 113  	}
	 114  	// Output:
	 115  	// Driver 1 calls T1: (T1 invokes T2: (This is T2))
	 116  	// Driver 2 calls T2: (This is T2)
	 117  }
	 118  
	 119  // This example demonstrates how to use one group of driver
	 120  // templates with distinct sets of helper templates.
	 121  func ExampleTemplate_share() {
	 122  	// Here we create a temporary directory and populate it with our sample
	 123  	// template definition files; usually the template files would already
	 124  	// exist in some location known to the program.
	 125  	dir := createTestDir([]templateFile{
	 126  		// T0.tmpl is a plain template file that just invokes T1.
	 127  		{"T0.tmpl", "T0 ({{.}} version) invokes T1: ({{template `T1`}})\n"},
	 128  		// T1.tmpl defines a template, T1 that invokes T2. Note T2 is not defined
	 129  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
	 130  	})
	 131  	// Clean up after the test; another quirk of running as an example.
	 132  	defer os.RemoveAll(dir)
	 133  
	 134  	// pattern is the glob pattern used to find all the template files.
	 135  	pattern := filepath.Join(dir, "*.tmpl")
	 136  
	 137  	// Here starts the example proper.
	 138  	// Load the drivers.
	 139  	drivers := template.Must(template.ParseGlob(pattern))
	 140  
	 141  	// We must define an implementation of the T2 template. First we clone
	 142  	// the drivers, then add a definition of T2 to the template name space.
	 143  
	 144  	// 1. Clone the helper set to create a new name space from which to run them.
	 145  	first, err := drivers.Clone()
	 146  	if err != nil {
	 147  		log.Fatal("cloning helpers: ", err)
	 148  	}
	 149  	// 2. Define T2, version A, and parse it.
	 150  	_, err = first.Parse("{{define `T2`}}T2, version A{{end}}")
	 151  	if err != nil {
	 152  		log.Fatal("parsing T2: ", err)
	 153  	}
	 154  
	 155  	// Now repeat the whole thing, using a different version of T2.
	 156  	// 1. Clone the drivers.
	 157  	second, err := drivers.Clone()
	 158  	if err != nil {
	 159  		log.Fatal("cloning drivers: ", err)
	 160  	}
	 161  	// 2. Define T2, version B, and parse it.
	 162  	_, err = second.Parse("{{define `T2`}}T2, version B{{end}}")
	 163  	if err != nil {
	 164  		log.Fatal("parsing T2: ", err)
	 165  	}
	 166  
	 167  	// Execute the templates in the reverse order to verify the
	 168  	// first is unaffected by the second.
	 169  	err = second.ExecuteTemplate(os.Stdout, "T0.tmpl", "second")
	 170  	if err != nil {
	 171  		log.Fatalf("second execution: %s", err)
	 172  	}
	 173  	err = first.ExecuteTemplate(os.Stdout, "T0.tmpl", "first")
	 174  	if err != nil {
	 175  		log.Fatalf("first: execution: %s", err)
	 176  	}
	 177  
	 178  	// Output:
	 179  	// T0 (second version) invokes T1: (T1 invokes T2: (T2, version B))
	 180  	// T0 (first version) invokes T1: (T1 invokes T2: (T2, version A))
	 181  }
	 182
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