template.go

     1  // Copyright 2011 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
     6  
     7  import (
     8  	"reflect"
     9  	"sync"
    10  	"text/template/parse"
    11  )
    12  
    13  // common holds the information shared by related templates.
    14  type common struct {
    15  	tmpl   map[string]*Template // Map from name to defined templates.
    16  	muTmpl sync.RWMutex         // protects tmpl
    17  	option option
    18  	// We use two maps, one for parsing and one for execution.
    19  	// This separation makes the API cleaner since it doesn't
    20  	// expose reflection to the client.
    21  	muFuncs    sync.RWMutex // protects parseFuncs and execFuncs
    22  	parseFuncs FuncMap
    23  	execFuncs  map[string]reflect.Value
    24  }
    25  
    26  // Template is the representation of a parsed template. The *parse.Tree
    27  // field is exported only for use by [html/template] and should be treated
    28  // as unexported by all other clients.
    29  type Template struct {
    30  	name string
    31  	*parse.Tree
    32  	*common
    33  	leftDelim  string
    34  	rightDelim string
    35  }
    36  
    37  // New allocates a new, undefined template with the given name.
    38  func New(name string) *Template {
    39  	t := &Template{
    40  		name: name,
    41  	}
    42  	t.init()
    43  	return t
    44  }
    45  
    46  // Name returns the name of the template.
    47  func (t *Template) Name() string {
    48  	return t.name
    49  }
    50  
    51  // New allocates a new, undefined template associated with the given one and with the same
    52  // delimiters. The association, which is transitive, allows one template to
    53  // invoke another with a {{template}} action.
    54  //
    55  // Because associated templates share underlying data, template construction
    56  // cannot be done safely in parallel. Once the templates are constructed, they
    57  // can be executed in parallel.
    58  func (t *Template) New(name string) *Template {
    59  	t.init()
    60  	nt := &Template{
    61  		name:       name,
    62  		common:     t.common,
    63  		leftDelim:  t.leftDelim,
    64  		rightDelim: t.rightDelim,
    65  	}
    66  	return nt
    67  }
    68  
    69  // init guarantees that t has a valid common structure.
    70  func (t *Template) init() {
    71  	if t.common == nil {
    72  		c := new(common)
    73  		c.tmpl = make(map[string]*Template)
    74  		c.parseFuncs = make(FuncMap)
    75  		c.execFuncs = make(map[string]reflect.Value)
    76  		t.common = c
    77  	}
    78  }
    79  
    80  // Clone returns a duplicate of the template, including all associated
    81  // templates. The actual representation is not copied, but the name space of
    82  // associated templates is, so further calls to [Template.Parse] in the copy will add
    83  // templates to the copy but not to the original. Clone can be used to prepare
    84  // common templates and use them with variant definitions for other templates
    85  // by adding the variants after the clone is made.
    86  func (t *Template) Clone() (*Template, error) {
    87  	nt := t.copy(nil)
    88  	nt.init()
    89  	if t.common == nil {
    90  		return nt, nil
    91  	}
    92  	t.muTmpl.RLock()
    93  	defer t.muTmpl.RUnlock()
    94  	for k, v := range t.tmpl {
    95  		if k == t.name {
    96  			nt.tmpl[t.name] = nt
    97  			continue
    98  		}
    99  		// The associated templates share nt's common structure.
   100  		tmpl := v.copy(nt.common)
   101  		nt.tmpl[k] = tmpl
   102  	}
   103  	t.muFuncs.RLock()
   104  	defer t.muFuncs.RUnlock()
   105  	for k, v := range t.parseFuncs {
   106  		nt.parseFuncs[k] = v
   107  	}
   108  	for k, v := range t.execFuncs {
   109  		nt.execFuncs[k] = v
   110  	}
   111  	return nt, nil
   112  }
   113  
   114  // copy returns a shallow copy of t, with common set to the argument.
   115  func (t *Template) copy(c *common) *Template {
   116  	return &Template{
   117  		name:       t.name,
   118  		Tree:       t.Tree,
   119  		common:     c,
   120  		leftDelim:  t.leftDelim,
   121  		rightDelim: t.rightDelim,
   122  	}
   123  }
   124  
   125  // AddParseTree associates the argument parse tree with the template t, giving
   126  // it the specified name. If the template has not been defined, this tree becomes
   127  // its definition. If it has been defined and already has that name, the existing
   128  // definition is replaced; otherwise a new template is created, defined, and returned.
   129  func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
   130  	t.init()
   131  	t.muTmpl.Lock()
   132  	defer t.muTmpl.Unlock()
   133  	nt := t
   134  	if name != t.name {
   135  		nt = t.New(name)
   136  	}
   137  	// Even if nt == t, we need to install it in the common.tmpl map.
   138  	if t.associate(nt, tree) || nt.Tree == nil {
   139  		nt.Tree = tree
   140  	}
   141  	return nt, nil
   142  }
   143  
   144  // Templates returns a slice of defined templates associated with t.
   145  func (t *Template) Templates() []*Template {
   146  	if t.common == nil {
   147  		return nil
   148  	}
   149  	// Return a slice so we don't expose the map.
   150  	t.muTmpl.RLock()
   151  	defer t.muTmpl.RUnlock()
   152  	m := make([]*Template, 0, len(t.tmpl))
   153  	for _, v := range t.tmpl {
   154  		m = append(m, v)
   155  	}
   156  	return m
   157  }
   158  
   159  // Delims sets the action delimiters to the specified strings, to be used in
   160  // subsequent calls to [Template.Parse], [Template.ParseFiles], or [Template.ParseGlob]. Nested template
   161  // definitions will inherit the settings. An empty delimiter stands for the
   162  // corresponding default: {{ or }}.
   163  // The return value is the template, so calls can be chained.
   164  func (t *Template) Delims(left, right string) *Template {
   165  	t.init()
   166  	t.leftDelim = left
   167  	t.rightDelim = right
   168  	return t
   169  }
   170  
   171  // Funcs adds the elements of the argument map to the template's function map.
   172  // It must be called before the template is parsed.
   173  // It panics if a value in the map is not a function with appropriate return
   174  // type or if the name cannot be used syntactically as a function in a template.
   175  // It is legal to overwrite elements of the map. The return value is the template,
   176  // so calls can be chained.
   177  func (t *Template) Funcs(funcMap FuncMap) *Template {
   178  	t.init()
   179  	t.muFuncs.Lock()
   180  	defer t.muFuncs.Unlock()
   181  	addValueFuncs(t.execFuncs, funcMap)
   182  	addFuncs(t.parseFuncs, funcMap)
   183  	return t
   184  }
   185  
   186  // Lookup returns the template with the given name that is associated with t.
   187  // It returns nil if there is no such template or the template has no definition.
   188  func (t *Template) Lookup(name string) *Template {
   189  	if t.common == nil {
   190  		return nil
   191  	}
   192  	t.muTmpl.RLock()
   193  	defer t.muTmpl.RUnlock()
   194  	return t.tmpl[name]
   195  }
   196  
   197  // Parse parses text as a template body for t.
   198  // Named template definitions ({{define ...}} or {{block ...}} statements) in text
   199  // define additional templates associated with t and are removed from the
   200  // definition of t itself.
   201  //
   202  // Templates can be redefined in successive calls to Parse.
   203  // A template definition with a body containing only white space and comments
   204  // is considered empty and will not replace an existing template's body.
   205  // This allows using Parse to add new named template definitions without
   206  // overwriting the main template body.
   207  func (t *Template) Parse(text string) (*Template, error) {
   208  	t.init()
   209  	t.muFuncs.RLock()
   210  	trees, err := parse.Parse(t.name, text, t.leftDelim, t.rightDelim, t.parseFuncs, builtins())
   211  	t.muFuncs.RUnlock()
   212  	if err != nil {
   213  		return nil, err
   214  	}
   215  	// Add the newly parsed trees, including the one for t, into our common structure.
   216  	for name, tree := range trees {
   217  		if _, err := t.AddParseTree(name, tree); err != nil {
   218  			return nil, err
   219  		}
   220  	}
   221  	return t, nil
   222  }
   223  
   224  // associate installs the new template into the group of templates associated
   225  // with t. The two are already known to share the common structure.
   226  // The boolean return value reports whether to store this tree as t.Tree.
   227  func (t *Template) associate(new *Template, tree *parse.Tree) bool {
   228  	if new.common != t.common {
   229  		panic("internal error: associate not common")
   230  	}
   231  	if old := t.tmpl[new.name]; old != nil && parse.IsEmptyTree(tree.Root) && old.Tree != nil {
   232  		// If a template by that name exists,
   233  		// don't replace it with an empty template.
   234  		return false
   235  	}
   236  	t.tmpl[new.name] = new
   237  	return true
   238  }
   239
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