text/template: revert CL 66410 "add break, continue actions in ranges"

The new break and continue actions do not work in html/template, and
fixing them requires thinking about security issues that seem too
tricky at this stage of the release. We will try again for 1.11.

Original CL description:

    text/template: add break, continue actions in ranges

    Adds the two range control actions "break" and "continue". They act the
    same as the Go keywords break and continue, but are simplified in that
    only the innermost range statement can be broken out of or continued.

    Fixes #20531

Updates #20531
Updates #23683

Change-Id: Ia7fd3c409163e3bcb5dc42947ae90b15bdf89853
Reviewed-on: https://go-review.googlesource.com/92155
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: ianlancetaylor

api/go1.10.txt

@@ -618,24 +618,6 @@ pkg syscall (windows-386), func CreateProcessAsUser(Token, *uint16, *uint16, *Se
 pkg syscall (windows-386), type SysProcAttr struct, Token Token
 pkg syscall (windows-amd64), func CreateProcessAsUser(Token, *uint16, *uint16, *SecurityAttributes, *SecurityAttributes, bool, uint32, *uint16, *uint16, *StartupInfo, *ProcessInformation) error
 pkg syscall (windows-amd64), type SysProcAttr struct, Token Token
-pkg text/template/parse, const NodeBreak = 20
-pkg text/template/parse, const NodeBreak NodeType
-pkg text/template/parse, const NodeContinue = 21
-pkg text/template/parse, const NodeContinue NodeType
-pkg text/template/parse, method (*BreakNode) Copy() Node
-pkg text/template/parse, method (*BreakNode) Position() Pos
-pkg text/template/parse, method (*BreakNode) String() string
-pkg text/template/parse, method (*BreakNode) Type() NodeType
-pkg text/template/parse, method (*ContinueNode) Copy() Node
-pkg text/template/parse, method (*ContinueNode) Position() Pos
-pkg text/template/parse, method (*ContinueNode) String() string
-pkg text/template/parse, method (*ContinueNode) Type() NodeType
-pkg text/template/parse, type BreakNode struct
-pkg text/template/parse, type BreakNode struct, embedded NodeType
-pkg text/template/parse, type BreakNode struct, embedded Pos
-pkg text/template/parse, type ContinueNode struct
-pkg text/template/parse, type ContinueNode struct, embedded NodeType
-pkg text/template/parse, type ContinueNode struct, embedded Pos
 pkg time, func LoadLocationFromTZData(string, []uint8) (*Location, error)
 pkg unicode, const Version = "10.0.0"
 pkg unicode, var Masaram_Gondi *RangeTable

doc/go1.10.html

@@ -1069,11 +1069,6 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="html/template"><dt><a href="/pkg/html/template/">html/template</a></dt>
 <dd>
 <p>
-The new actions <code>{{"{{break}}"}}</code> and <code>{{"{{continue}}"}}</code>
-break out of the innermost <code>{{"{{range"}}</code>&nbsp;...<code>}}</code> loop,
-like the corresponding Go statements.
-</p>
-<p>
 The new <a href="/pkg/html/template#Srcset"><code>Srcset</code></a> content
 type allows for proper handling of values within the
 <a href="https://w3c.github.io/html/semantics-embedded-content.html#element-attrdef-img-srcset"><code>srcset</code></a>
@@ -1411,15 +1406,6 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 </p>
 </dl>
 
-<dl id="text/template"><dt><a href="/pkg/text/template/">text/template</a></dt>
-<dd>
-<p>
-The new actions <code>{{"{{break}}"}}</code> and <code>{{"{{continue}}"}}</code>
-break out of the innermost <code>{{"{{range"}}</code>&nbsp;...<code>}}</code> loop,
-like the corresponding Go statements.
-</p>
-</dl>
-
 <dl id="time"><dt><a href="/pkg/time/">time</a></dt>
 <dd>
 <p>

src/text/template/doc.go

@@ -110,12 +110,6 @@ data, defined in detail in the corresponding sections that follow.
 		T0 is executed; otherwise, dot is set to the successive elements
 		of the array, slice, or map and T1 is executed.
 
-	{{break}}
-		Break out of the surrounding range loop.
-
-	{{continue}}
-		Begin the next iteration of the surrounding range loop.
-
 	{{template "name"}}
 		The template with the specified name is executed with nil data.
 

src/text/template/exec.go

@@ -25,12 +25,11 @@ const maxExecDepth = 100000
 // template so that multiple executions of the same template
 // can execute in parallel.
 type state struct {
-	tmpl       *Template
-	wr         io.Writer
-	node       parse.Node // current node, for errors.
-	vars       []variable // push-down stack of variable values.
-	depth      int        // the height of the stack of executing templates.
-	rangeDepth int        // nesting level of range loops.
+	tmpl  *Template
+	wr    io.Writer
+	node  parse.Node // current node, for errors
+	vars  []variable // push-down stack of variable values.
+	depth int        // the height of the stack of executing templates.
 }
 
 // variable holds the dynamic value of a variable such as $, $x etc.
@@ -221,17 +220,9 @@ func (t *Template) DefinedTemplates() string {
 	return s
 }
 
-type rangeControl int8
-
-const (
-	rangeNone     rangeControl = iota // no action.
-	rangeBreak                        // break out of range.
-	rangeContinue                     // continues next range iteration.
-)
-
 // Walk functions step through the major pieces of the template structure,
 // generating output as they go.
-func (s *state) walk(dot reflect.Value, node parse.Node) rangeControl {
+func (s *state) walk(dot reflect.Value, node parse.Node) {
 	s.at(node)
 	switch node := node.(type) {
 	case *parse.ActionNode:
@@ -242,42 +233,29 @@ func (s *state) walk(dot reflect.Value, node parse.Node) rangeControl {
 			s.printValue(node, val)
 		}
 	case *parse.IfNode:
-		return s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
+		s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
 	case *parse.ListNode:
 		for _, node := range node.Nodes {
-			if c := s.walk(dot, node); c != rangeNone {
-				return c
-			}
+			s.walk(dot, node)
 		}
 	case *parse.RangeNode:
-		return s.walkRange(dot, node)
+		s.walkRange(dot, node)
 	case *parse.TemplateNode:
 		s.walkTemplate(dot, node)
 	case *parse.TextNode:
 		if _, err := s.wr.Write(node.Text); err != nil {
 			s.writeError(err)
 		}
 	case *parse.WithNode:
-		return s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
-	case *parse.BreakNode:
-		if s.rangeDepth == 0 {
-			s.errorf("invalid break outside of range")
-		}
-		return rangeBreak
-	case *parse.ContinueNode:
-		if s.rangeDepth == 0 {
-			s.errorf("invalid continue outside of range")
-		}
-		return rangeContinue
+		s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
 	default:
 		s.errorf("unknown node: %s", node)
 	}
-	return rangeNone
 }
 
 // walkIfOrWith walks an 'if' or 'with' node. The two control structures
 // are identical in behavior except that 'with' sets dot.
-func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) rangeControl {
+func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) {
 	defer s.pop(s.mark())
 	val := s.evalPipeline(dot, pipe)
 	truth, ok := isTrue(val)
@@ -286,14 +264,13 @@ func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.
 	}
 	if truth {
 		if typ == parse.NodeWith {
-			return s.walk(val, list)
+			s.walk(val, list)
 		} else {
-			return s.walk(dot, list)
+			s.walk(dot, list)
 		}
 	} else if elseList != nil {
-		return s.walk(dot, elseList)
+		s.walk(dot, elseList)
 	}
-	return rangeNone
 }
 
 // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
@@ -331,14 +308,13 @@ func isTrue(val reflect.Value) (truth, ok bool) {
 	return truth, true
 }
 
-func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) rangeControl {
+func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 	s.at(r)
 	defer s.pop(s.mark())
 	val, _ := indirect(s.evalPipeline(dot, r.Pipe))
 	// mark top of stack before any variables in the body are pushed.
 	mark := s.mark()
-	s.rangeDepth++
-	oneIteration := func(index, elem reflect.Value) rangeControl {
+	oneIteration := func(index, elem reflect.Value) {
 		// Set top var (lexically the second if there are two) to the element.
 		if len(r.Pipe.Decl) > 0 {
 			s.setVar(1, elem)
@@ -347,33 +323,26 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) rangeControl {
 		if len(r.Pipe.Decl) > 1 {
 			s.setVar(2, index)
 		}
-		ctrl := s.walk(elem, r.List)
+		s.walk(elem, r.List)
 		s.pop(mark)
-		return ctrl
 	}
 	switch val.Kind() {
 	case reflect.Array, reflect.Slice:
 		if val.Len() == 0 {
 			break
 		}
 		for i := 0; i < val.Len(); i++ {
-			if ctrl := oneIteration(reflect.ValueOf(i), val.Index(i)); ctrl == rangeBreak {
-				break
-			}
+			oneIteration(reflect.ValueOf(i), val.Index(i))
 		}
-		s.rangeDepth--
-		return rangeNone
+		return
 	case reflect.Map:
 		if val.Len() == 0 {
 			break
 		}
 		for _, key := range sortKeys(val.MapKeys()) {
-			if ctrl := oneIteration(key, val.MapIndex(key)); ctrl == rangeBreak {
-				break
-			}
+			oneIteration(key, val.MapIndex(key))
 		}
-		s.rangeDepth--
-		return rangeNone
+		return
 	case reflect.Chan:
 		if val.IsNil() {
 			break
@@ -384,25 +353,20 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) rangeControl {
 			if !ok {
 				break
 			}
-			if ctrl := oneIteration(reflect.ValueOf(i), elem); ctrl == rangeBreak {
-				break
-			}
+			oneIteration(reflect.ValueOf(i), elem)
 		}
 		if i == 0 {
 			break
 		}
-		s.rangeDepth--
-		return rangeNone
+		return
 	case reflect.Invalid:
 		break // An invalid value is likely a nil map, etc. and acts like an empty map.
 	default:
 		s.errorf("range can't iterate over %v", val)
 	}
-	s.rangeDepth--
 	if r.ElseList != nil {
-		return s.walk(dot, r.ElseList)
+		s.walk(dot, r.ElseList)
 	}
-	return rangeNone
 }
 
 func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {

src/text/template/exec_test.go

@@ -513,10 +513,6 @@ var execTests = []execTest{
 	{"declare in range", "{{range $x := .PSI}}<{{$foo:=$x}}{{$x}}>{{end}}", "<21><22><23>", tVal, true},
 	{"range count", `{{range $i, $x := count 5}}[{{$i}}]{{$x}}{{end}}`, "[0]a[1]b[2]c[3]d[4]e", tVal, true},
 	{"range nil count", `{{range $i, $x := count 0}}{{else}}empty{{end}}`, "empty", tVal, true},
-	{"range quick break", `{{range .SI}}{{break}}{{.}}{{end}}`, "", tVal, true},
-	{"range break after two", `{{range $i, $x := .SI}}{{if ge $i 2}}{{break}}{{end}}{{.}}{{end}}`, "34", tVal, true},
-	{"range continue", `{{range .SI}}{{continue}}{{.}}{{end}}`, "", tVal, true},
-	{"range continue condition", `{{range .SI}}{{if eq . 3 }}{{continue}}{{end}}{{.}}{{end}}`, "45", tVal, true},
 
 	// Cute examples.
 	{"or as if true", `{{or .SI "slice is empty"}}`, "[3 4 5]", tVal, true},

src/text/template/parse/lex.go

@@ -60,8 +60,6 @@ const (
 	// Keywords appear after all the rest.
 	itemKeyword  // used only to delimit the keywords
 	itemBlock    // block keyword
-	itemBreak    // break keyword
-	itemContinue // continue keyword
 	itemDot      // the cursor, spelled '.'
 	itemDefine   // define keyword
 	itemElse     // else keyword
@@ -76,8 +74,6 @@ const (
 var key = map[string]itemType{
 	".":        itemDot,
 	"block":    itemBlock,
-	"break":    itemBreak,
-	"continue": itemContinue,
 	"define":   itemDefine,
 	"else":     itemElse,
 	"end":      itemEnd,

src/text/template/parse/lex_test.go

@@ -192,7 +192,7 @@ var lexTests = []lexTest{
 		tRight,
 		tEOF,
 	}},
-	{"keywords", "{{range if else end with break continue}}", []item{
+	{"keywords", "{{range if else end with}}", []item{
 		tLeft,
 		mkItem(itemRange, "range"),
 		tSpace,
@@ -203,10 +203,6 @@ var lexTests = []lexTest{
 		mkItem(itemEnd, "end"),
 		tSpace,
 		mkItem(itemWith, "with"),
-		tSpace,
-		mkItem(itemBreak, "break"),
-		tSpace,
-		mkItem(itemContinue, "continue"),
 		tRight,
 		tEOF,
 	}},

src/text/template/parse/node.go

@@ -69,8 +69,6 @@ const (
 	NodeTemplate                   // A template invocation action.
 	NodeVariable                   // A $ variable.
 	NodeWith                       // A with action.
-	NodeBreak                      // A break action.
-	NodeContinue                   // A continue action.
 )
 
 // Nodes.
@@ -798,68 +796,6 @@ func (r *RangeNode) Copy() Node {
 	return r.tr.newRange(r.Pos, r.Line, r.Pipe.CopyPipe(), r.List.CopyList(), r.ElseList.CopyList())
 }
 
-// BreakNode represents a {{break}} action.
-type BreakNode struct {
-	NodeType
-	Pos
-	tr *Tree
-}
-
-func (t *Tree) newBreak(pos Pos) *BreakNode {
-	return &BreakNode{NodeType: NodeBreak, Pos: pos, tr: t}
-}
-
-func (b *BreakNode) Type() NodeType {
-	return b.NodeType
-}
-
-func (b *BreakNode) String() string {
-	return "{{break}}"
-}
-
-func (b *BreakNode) Copy() Node {
-	return b.tr.newBreak(b.Pos)
-}
-
-func (b *BreakNode) Position() Pos {
-	return b.Pos
-}
-
-func (b *BreakNode) tree() *Tree {
-	return b.tr
-}
-
-// ContinueNode represents a {{continue}} action.
-type ContinueNode struct {
-	NodeType
-	Pos
-	tr *Tree
-}
-
-func (t *Tree) newContinue(pos Pos) *ContinueNode {
-	return &ContinueNode{NodeType: NodeContinue, Pos: pos, tr: t}
-}
-
-func (c *ContinueNode) Type() NodeType {
-	return c.NodeType
-}
-
-func (c *ContinueNode) String() string {
-	return "{{continue}}"
-}
-
-func (c *ContinueNode) Copy() Node {
-	return c.tr.newContinue(c.Pos)
-}
-
-func (c *ContinueNode) Position() Pos {
-	return c.Pos
-}
-
-func (c *ContinueNode) tree() *Tree {
-	return c.tr
-}
-
 // WithNode represents a {{with}} action and its commands.
 type WithNode struct {
 	BranchNode