Add render template hooks for links and images

This commit also

* revises the change detection for templates used by content files in server mode.
* Adds a Page.RenderString method

Fixes #6545
Fixes #4663
Closes #6043

3 files changed, 119 insertions, 9 deletions

diff --git a/tpl/internal/go_templates/texttemplate/exec.go b/tpl/internal/go_templates/texttemplate/exec.go
index db64edcb2..078bcf643 100644
--- a/tpl/internal/go_templates/texttemplate/exec.go
+++ b/tpl/internal/go_templates/texttemplate/exec.go
@@ -658,7 +658,7 @@ var (
 // evalCall executes a function or method call. If it's a method, fun already has the receiver bound, so
 // it looks just like a function call. The arg list, if non-nil, includes (in the manner of the shell), arg[0]
 // as the function itself.
-func (s *state) evalCall(dot, fun reflect.Value, node parse.Node, name string, args []parse.Node, final reflect.Value) reflect.Value {
+func (s *state) evalCallOld(dot, fun reflect.Value, node parse.Node, name string, args []parse.Node, final reflect.Value) reflect.Value {
 	if args != nil {
 		args = args[1:] // Zeroth arg is function name/node; not passed to function.
 	}
diff --git a/tpl/internal/go_templates/texttemplate/hugo_template.go b/tpl/internal/go_templates/texttemplate/hugo_template.go
index be8a5558f..a39f027fb 100644
--- a/tpl/internal/go_templates/texttemplate/hugo_template.go
+++ b/tpl/internal/go_templates/texttemplate/hugo_template.go
@@ -34,8 +34,9 @@ type Preparer interface {
 
 // ExecHelper allows some custom eval hooks.
 type ExecHelper interface {
-	GetFunc(name string) (reflect.Value, bool)
-	GetMapValue(receiver, key reflect.Value) (reflect.Value, bool)
+	GetFunc(tmpl Preparer, name string) (reflect.Value, bool)
+	GetMethod(tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value)
+	GetMapValue(tmpl Preparer, receiver, key reflect.Value) (reflect.Value, bool)
 }
 
 // Executer executes a given template.
@@ -64,6 +65,7 @@ func (t *executer) Execute(p Preparer, wr io.Writer, data interface{}) error {
 
 	state := &state{
 		helper: t.helper,
+		prep:   p,
 		tmpl:   tmpl,
 		wr:     wr,
 		vars:   []variable{{"$", value}},
@@ -75,7 +77,6 @@ func (t *executer) Execute(p Preparer, wr io.Writer, data interface{}) error {
 
 // Prepare returns a template ready for execution.
 func (t *Template) Prepare() (*Template, error) {
-
 	return t, nil
 }
 
@@ -95,6 +96,7 @@ func (t *Template) executeWithState(state *state, value reflect.Value) (err erro
 // can execute in parallel.
 type state struct {
 	tmpl   *Template
+	prep   Preparer   // Added for Hugo.
 	helper ExecHelper // Added for Hugo.
 	wr     io.Writer
 	node   parse.Node // current node, for errors
@@ -110,7 +112,7 @@ func (s *state) evalFunction(dot reflect.Value, node *parse.IdentifierNode, cmd
 	var ok bool
 	if s.helper != nil {
 		// Added for Hugo.
-		function, ok = s.helper.GetFunc(name)
+		function, ok = s.helper.GetFunc(s.prep, name)
 	}
 
 	if !ok {
@@ -148,9 +150,23 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 	if ptr.Kind() != reflect.Interface && ptr.Kind() != reflect.Ptr && ptr.CanAddr() {
 		ptr = ptr.Addr()
 	}
-	if method := ptr.MethodByName(fieldName); method.IsValid() {
+	// Added for Hugo.
+	var first reflect.Value
+	var method reflect.Value
+	if s.helper != nil {
+		method, first = s.helper.GetMethod(s.prep, ptr, fieldName)
+	} else {
+		method = ptr.MethodByName(fieldName)
+	}
+
+	if method.IsValid() {
+		if first != zero {
+			return s.evalCall(dot, method, node, fieldName, args, final, first)
+		}
+
 		return s.evalCall(dot, method, node, fieldName, args, final)
 	}
+
 	hasArgs := len(args) > 1 || final != missingVal
 	// It's not a method; must be a field of a struct or an element of a map.
 	switch receiver.Kind() {
@@ -177,7 +193,7 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 			var result reflect.Value
 			if s.helper != nil {
 				// Added for Hugo.
-				result, _ = s.helper.GetMapValue(receiver, nameVal)
+				result, _ = s.helper.GetMapValue(s.prep, receiver, nameVal)
 			} else {
 				result = receiver.MapIndex(nameVal)
 			}
@@ -209,3 +225,79 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 	s.errorf("can't evaluate field %s in type %s", fieldName, typ)
 	panic("not reached")
 }
+
+// evalCall executes a function or method call. If it's a method, fun already has the receiver bound, so
+// it looks just like a function call. The arg list, if non-nil, includes (in the manner of the shell), arg[0]
+// as the function itself.
+func (s *state) evalCall(dot, fun reflect.Value, node parse.Node, name string, args []parse.Node, final reflect.Value, first ...reflect.Value) reflect.Value {
+	if args != nil {
+		args = args[1:] // Zeroth arg is function name/node; not passed to function.
+	}
+	typ := fun.Type()
+	numFirst := len(first)
+	numIn := len(args) + numFirst // // Added for Hugo
+	if final != missingVal {
+		numIn++
+	}
+	numFixed := len(args) + len(first)
+	if typ.IsVariadic() {
+		numFixed = typ.NumIn() - 1 // last arg is the variadic one.
+		if numIn < numFixed {
+			s.errorf("wrong number of args for %s: want at least %d got %d", name, typ.NumIn()-1, len(args))
+		}
+	} else if numIn != typ.NumIn() {
+		s.errorf("wrong number of args for %s: want %d got %d", name, typ.NumIn(), numIn)
+	}
+	if !goodFunc(typ) {
+		// TODO: This could still be a confusing error; maybe goodFunc should provide info.
+		s.errorf("can't call method/function %q with %d results", name, typ.NumOut())
+	}
+	// Build the arg list.
+	argv := make([]reflect.Value, numIn)
+	// Args must be evaluated. Fixed args first.
+	i := len(first)
+	for ; i < numFixed && i < len(args)+numFirst; i++ {
+		argv[i] = s.evalArg(dot, typ.In(i), args[i-numFirst])
+	}
+	// Now the ... args.
+	if typ.IsVariadic() {
+		argType := typ.In(typ.NumIn() - 1).Elem() // Argument is a slice.
+		for ; i < len(args)+numFirst; i++ {
+			argv[i] = s.evalArg(dot, argType, args[i-numFirst])
+		}
+
+	}
+	// Add final value if necessary.
+	if final != missingVal {
+		t := typ.In(typ.NumIn() - 1)
+		if typ.IsVariadic() {
+			if numIn-1 < numFixed {
+				// The added final argument corresponds to a fixed parameter of the function.
+				// Validate against the type of the actual parameter.
+				t = typ.In(numIn - 1)
+			} else {
+				// The added final argument corresponds to the variadic part.
+				// Validate against the type of the elements of the variadic slice.
+				t = t.Elem()
+			}
+		}
+		argv[i] = s.validateType(final, t)
+	}
+
+	// Added for Hugo
+	for i := 0; i < len(first); i++ {
+		argv[i] = s.validateType(first[i], typ.In(i))
+	}
+
+	v, err := safeCall(fun, argv)
+	// If we have an error that is not nil, stop execution and return that
+	// error to the caller.
+	if err != nil {
+		s.at(node)
+		s.errorf("error calling %s: %v", name, err)
+	}
+	if v.Type() == reflectValueType {
+		v = v.Interface().(reflect.Value)
+	}
+	return v
+}
diff --git a/tpl/internal/go_templates/texttemplate/hugo_template_test.go b/tpl/internal/go_templates/texttemplate/hugo_template_test.go
index 2424a0a48..98a2575eb 100644
--- a/tpl/internal/go_templates/texttemplate/hugo_template_test.go
+++ b/tpl/internal/go_templates/texttemplate/hugo_template_test.go
@@ -27,10 +27,18 @@ type TestStruct struct {
 	M map[string]string
 }
 
+func (t TestStruct) Hello1(arg string) string {
+	return arg
+}
+
+func (t TestStruct) Hello2(arg1, arg2 string) string {
+	return arg1 + " " + arg2
+}
+
 type execHelper struct {
 }
 
-func (e *execHelper) GetFunc(name string) (reflect.Value, bool) {
+func (e *execHelper) GetFunc(tmpl Preparer, name string) (reflect.Value, bool) {
 	if name == "print" {
 		return zero, false
 	}
@@ -39,11 +47,19 @@ func (e *execHelper) GetFunc(name string) (reflect.Value, bool) {
 	}), true
 }
 
-func (e *execHelper) GetMapValue(m, key reflect.Value) (reflect.Value, bool) {
+func (e *execHelper) GetMapValue(tmpl Preparer, m, key reflect.Value) (reflect.Value, bool) {
 	key = reflect.ValueOf(strings.ToLower(key.String()))
 	return m.MapIndex(key), true
 }
 
+func (e *execHelper) GetMethod(tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
+	if name != "Hello1" {
+		return zero, zero
+	}
+	m := receiver.MethodByName("Hello2")
+	return m, reflect.ValueOf("v2")
+}
+
 func TestTemplateExecutor(t *testing.T) {
 	c := qt.New(t)
 
@@ -51,6 +67,7 @@ func TestTemplateExecutor(t *testing.T) {
 {{ print "foo" }}
 {{ printf "hugo" }}
 Map: {{ .M.A }}
+Method: {{ .Hello1 "v1" }}
 
 `)
 
@@ -67,5 +84,6 @@ Map: {{ .M.A }}
 	c.Assert(got, qt.Contains, "foo")
 	c.Assert(got, qt.Contains, "hello hugo")
 	c.Assert(got, qt.Contains, "Map: av")
+	c.Assert(got, qt.Contains, "Method: v2 v1")
 
 }