feat: add break, continue actions in ranges

This is copied verbatim from https://go-review.googlesource.com/c/go/+/66410/. The above commit was reverted due to issues with html/template (see golang/go#23683
). However, as we don't have such issues, there seems to be no issue in adding it to this fork. Changes pass all tests.

exec.go

@@ -38,6 +38,7 @@ type state struct {
 	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.
 	operations int
 
 	parent *state
@@ -247,9 +248,17 @@ 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) {
+func (s *state) walk(dot reflect.Value, node parse.Node) rangeControl {
 	s.at(node)
 	switch node := node.(type) {
 	case *parse.ActionNode:
@@ -260,29 +269,42 @@ func (s *state) walk(dot reflect.Value, node parse.Node) {
 			s.printValue(node, val)
 		}
 	case *parse.IfNode:
-		s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
+		return s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
 	case *parse.ListNode:
 		for _, node := range node.Nodes {
-			s.walk(dot, node)
+			if c := s.walk(dot, node); c != rangeNone {
+				return c
+			}
 		}
 	case *parse.RangeNode:
-		s.walkRange(dot, node)
+		return 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:
-		s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
+		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
 	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) {
+func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) rangeControl {
 	defer s.pop(s.mark())
 	val := s.evalPipeline(dot, pipe)
 	truth, ok := isTrue(val)
@@ -291,13 +313,14 @@ func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.
 	}
 	if truth {
 		if typ == parse.NodeWith {
-			s.walk(val, list)
+			return s.walk(val, list)
 		} else {
-			s.walk(dot, list)
+			return s.walk(dot, list)
 		}
 	} else if elseList != nil {
-		s.walk(dot, elseList)
+		return s.walk(dot, elseList)
 	}
+	return rangeNone
 }
 
 // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
@@ -335,15 +358,16 @@ func isTrue(val reflect.Value) (truth, ok bool) {
 	return truth, true
 }
 
-func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
+func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) rangeControl {
 	s.incrOPs(1)
 
 	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()
-	oneIteration := func(index, elem reflect.Value) {
+	s.rangeDepth++
+	oneIteration := func(index, elem reflect.Value) rangeControl {
 		s.incrOPs(1)
 
 		// Set top var (lexically the second if there are two) to the element.
@@ -354,26 +378,33 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 		if len(r.Pipe.Decl) > 1 {
 			s.setTopVar(2, index)
 		}
-		s.walk(elem, r.List)
+		ctrl := 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++ {
-			oneIteration(reflect.ValueOf(i), val.Index(i))
+			if ctrl := oneIteration(reflect.ValueOf(i), val.Index(i)); ctrl == rangeBreak {
+				break
+			}
 		}
-		return
+		s.rangeDepth--
+		return rangeNone
 	case reflect.Map:
 		if val.Len() == 0 {
 			break
 		}
 		for _, key := range sortKeys(val.MapKeys()) {
-			oneIteration(key, val.MapIndex(key))
+			if ctrl := oneIteration(key, val.MapIndex(key)); ctrl == rangeBreak {
+				break
+			}
 		}
-		return
+		s.rangeDepth--
+		return rangeNone
 	case reflect.Chan:
 		if val.IsNil() {
 			break
@@ -384,20 +415,25 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 			if !ok {
 				break
 			}
-			oneIteration(reflect.ValueOf(i), elem)
+			if ctrl := oneIteration(reflect.ValueOf(i), elem); ctrl == rangeBreak {
+				break
+			}
 		}
 		if i == 0 {
 			break
 		}
-		return
+		s.rangeDepth--
+		return rangeNone
 	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 {
-		s.walk(dot, r.ElseList)
+		return s.walk(dot, r.ElseList)
 	}
+	return rangeNone
 }
 
 func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {

exec_test.go

@@ -534,6 +534,10 @@ 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},

parse/lex.go

@@ -61,6 +61,8 @@ 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
@@ -75,6 +77,8 @@ const (
 var key = map[string]itemType{
 	".":        itemDot,
 	"block":    itemBlock,
+	"break":    itemBreak,
+	"continue": itemContinue,
 	"define":   itemDefine,
 	"else":     itemElse,
 	"end":      itemEnd,

parse/lex_test.go

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

parse/node.go

@@ -69,6 +69,8 @@ const (
 	NodeTemplate                   // A template invocation action.
 	NodeVariable                   // A $ variable.
 	NodeWith                       // A with action.
+	NodeBreak                      // A break action.
+	NodeContinue                   // A continue action.
 )
 
 // Nodes.
@@ -798,6 +800,58 @@ 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

parse/parse.go

@@ -23,12 +23,13 @@ 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
+	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.
 }
 
 // Copy returns a copy of the Tree. Any parsing state is discarded.
@@ -219,6 +220,7 @@ 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
@@ -373,6 +375,10 @@ 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()
@@ -461,7 +467,13 @@ 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:
@@ -506,6 +518,26 @@ 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}}