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 <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

10 files changed, 31 insertions, 225 deletions

diff --git a/api/go1.10.txt b/api/go1.10.txt
index f17e54343f..250c10f6ab 100644
--- a/api/go1.10.txt
+++ b/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
diff --git a/doc/go1.10.html b/doc/go1.10.html
index aef3be2bef..5885176f46 100644
--- a/doc/go1.10.html
+++ b/doc/go1.10.html
@@ -1069,11 +1069,6 @@ now implement those interfaces.
 <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 @@ is now implemented.
 </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>
diff --git a/src/text/template/doc.go b/src/text/template/doc.go
index f7609293ce..d174ebd9cf 100644
--- a/src/text/template/doc.go
+++ b/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.
 
diff --git a/src/text/template/exec.go b/src/text/template/exec.go
index 87cf1e9b1c..83c38cdf13 100644
--- a/src/text/template/exec.go
+++ b/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:
@@ -242,15 +233,13 @@ 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:
@@ -258,26 +247,15 @@ func (s *state) walk(dot reflect.Value, node parse.Node) rangeControl {
 			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)
@@ -347,9 +323,8 @@ 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:
@@ -357,23 +332,17 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) rangeControl {
 			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) {
diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index 79b504f8a4..d0cda6bd62 100644
--- a/src/text/template/exec_test.go
+++ b/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},
diff --git a/src/text/template/parse/lex.go b/src/text/template/parse/lex.go
index da766cc7c3..e112cb7714 100644
--- a/src/text/template/parse/lex.go
+++ b/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,
diff --git a/src/text/template/parse/lex_test.go b/src/text/template/parse/lex_test.go
index ca7c3f64bc..cb01cd98b6 100644
--- a/src/text/template/parse/lex_test.go
+++ b/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,
 	}},
diff --git a/src/text/template/parse/node.go b/src/text/template/parse/node.go
index 7e16349b31..55ff46c17a 100644
--- a/src/text/template/parse/node.go
+++ b/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
diff --git a/src/text/template/parse/parse.go b/src/text/template/parse/parse.go
index ad9c051978..a91a544ce0 100644
--- a/src/text/template/parse/parse.go
+++ b/src/text/template/parse/parse.go
@@ -23,13 +23,12 @@ type Tree struct {
 	Root      *ListNode // top-level root of the tree.
 	text      string    // text parsed to create the template (or its parent)
 	// Parsing only; cleared after parse.
-	funcs      []map[string]interface{}
-	lex        *lexer
-	token      [3]item // three-token lookahead for parser.
-	peekCount  int
-	vars       []string // variables defined at the moment.
-	treeSet    map[string]*Tree
-	rangeDepth int // nesting level of range loops.
+	funcs     []map[string]interface{}
+	lex       *lexer
+	token     [3]item // three-token lookahead for parser.
+	peekCount int
+	vars      []string // variables defined at the moment.
+	treeSet   map[string]*Tree
 }
 
 // Copy returns a copy of the Tree. Any parsing state is discarded.
@@ -220,7 +219,6 @@ func (t *Tree) stopParse() {
 	t.vars = nil
 	t.funcs = nil
 	t.treeSet = nil
-	t.rangeDepth = 0
 }
 
 // Parse parses the template definition string to construct a representation of
@@ -375,10 +373,6 @@ func (t *Tree) action() (n Node) {
 		return t.templateControl()
 	case itemWith:
 		return t.withControl()
-	case itemBreak:
-		return t.breakControl()
-	case itemContinue:
-		return t.continueControl()
 	}
 	t.backup()
 	token := t.peek()
@@ -459,13 +453,7 @@ func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int
 	defer t.popVars(len(t.vars))
 	pipe = t.pipeline(context)
 	var next Node
-	if context == "range" {
-		t.rangeDepth++
-	}
 	list, next = t.itemList()
-	if context == "range" {
-		t.rangeDepth--
-	}
 	switch next.Type() {
 	case nodeEnd: //done
 	case nodeElse:
@@ -510,26 +498,6 @@ func (t *Tree) rangeControl() Node {
 	return t.newRange(t.parseControl(false, "range"))
 }
 
-// Break:
-//	{{break}}
-// Break keyword is past.
-func (t *Tree) breakControl() Node {
-	if t.rangeDepth == 0 {
-		t.errorf("unexpected break outside of range")
-	}
-	return t.newBreak(t.expect(itemRightDelim, "break").pos)
-}
-
-// Continue:
-//	{{continue}}
-// Continue keyword is past.
-func (t *Tree) continueControl() Node {
-	if t.rangeDepth == 0 {
-		t.errorf("unexpected continue outside of range")
-	}
-	return t.newContinue(t.expect(itemRightDelim, "continue").pos)
-}
-
 // With:
 //	{{with pipeline}} itemList {{end}}
 //	{{with pipeline}} itemList {{else}} itemList {{end}}
diff --git a/src/text/template/parse/parse_test.go b/src/text/template/parse/parse_test.go
index aade33ea48..81f14aca98 100644
--- a/src/text/template/parse/parse_test.go
+++ b/src/text/template/parse/parse_test.go
@@ -218,12 +218,6 @@ var parseTests = []parseTest{
 		`{{range $x := .SI}}{{.}}{{end}}`},
 	{"range 2 vars", "{{range $x, $y := .SI}}{{.}}{{end}}", noError,
 		`{{range $x, $y := .SI}}{{.}}{{end}}`},
-	{"range []int with break", "{{range .SI}}{{break}}{{.}}{{end}}", noError,
-		`{{range .SI}}{{break}}{{.}}{{end}}`},
-	{"range []int with break in else", "{{range .SI}}{{range .SI}}{{.}}{{else}}{{break}}{{end}}{{end}}", noError,
-		`{{range .SI}}{{range .SI}}{{.}}{{else}}{{break}}{{end}}{{end}}`},
-	{"range []int with continue", "{{range .SI}}{{continue}}{{.}}{{end}}", noError,
-		`{{range .SI}}{{continue}}{{.}}{{end}}`},
 	{"constants", "{{range .SI 1 -3.2i true false 'a' nil}}{{end}}", noError,
 		`{{range .SI 1 -3.2i true false 'a' nil}}{{end}}`},
 	{"template", "{{template `x`}}", noError,
@@ -294,12 +288,6 @@ var parseTests = []parseTest{
 	{"empty pipeline", `{{printf "%d" ( ) }}`, hasError, ""},
 	// Missing pipeline in block
 	{"block definition", `{{block "foo"}}hello{{end}}`, hasError, ""},
-	// Invalid range control
-	{"break outside of range", `{{break}}`, hasError, ""},
-	{"break in range else, outside of range", `{{range .}}{{.}}{{else}}{{break}}{{end}}`, hasError, ""},
-	{"continue outside of range", `{{continue}}`, hasError, ""},
-	{"continue in range else, outside of range", `{{range .}}{{.}}{{else}}{{continue}}{{end}}`, hasError, ""},
-	{"additional break data", `{{range .}}{{break label}}{{end}}`, hasError, ""},
 }
 
 var builtins = map[string]interface{}{