Break and continue for range loops was accepted as a proposal in June 2017.
It was implemented in CL 66410 (Oct 2017)
but then rolled back in CL 92155 (Feb 2018)
because html/template changes had not been implemented.
This CL reimplements break and continue in text/template
and then adds support for them in html/template as well.
Fixes #20531.
Change-Id: I05330482a976f1c078b4b49c2287bd9031bb7616
Reviewed-on: https://go-review.googlesource.com/c/go/+/321491
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
import (
"fmt"
+ "text/template/parse"
)
// context describes the state an HTML parser must be in when it reaches the
jsCtx jsCtx
attr attr
element element
+ n parse.Node // for range break/continue
err *Error
}
// stateError is an infectious error state outside any valid
// HTML/CSS/JS construct.
stateError
+ // stateDead marks unreachable code after a {{break}} or {{continue}}.
+ stateDead
)
// isComment is true for any state that contains content meant for template
actionNodeEdits map[*parse.ActionNode][]string
templateNodeEdits map[*parse.TemplateNode]string
textNodeEdits map[*parse.TextNode][]byte
+ // rangeContext holds context about the current range loop.
+ rangeContext *rangeContext
+}
+
+// rangeContext holds information about the current range loop.
+type rangeContext struct {
+ outer *rangeContext // outer loop
+ breaks []context // context at each break action
+ continues []context // context at each continue action
}
// makeEscaper creates a blank escaper for the given set.
map[*parse.ActionNode][]string{},
map[*parse.TemplateNode]string{},
map[*parse.TextNode][]byte{},
+ nil,
}
}
switch n := n.(type) {
case *parse.ActionNode:
return e.escapeAction(c, n)
+ case *parse.BreakNode:
+ c.n = n
+ e.rangeContext.breaks = append(e.rangeContext.breaks, c)
+ return context{state: stateDead}
case *parse.CommentNode:
return c
+ case *parse.ContinueNode:
+ c.n = n
+ e.rangeContext.continues = append(e.rangeContext.breaks, c)
+ return context{state: stateDead}
case *parse.IfNode:
return e.escapeBranch(c, &n.BranchNode, "if")
case *parse.ListNode:
if b.state == stateError {
return b
}
+ if a.state == stateDead {
+ return b
+ }
+ if b.state == stateDead {
+ return a
+ }
if a.eq(b) {
return a
}
// escapeBranch escapes a branch template node: "if", "range" and "with".
func (e *escaper) escapeBranch(c context, n *parse.BranchNode, nodeName string) context {
+ if nodeName == "range" {
+ e.rangeContext = &rangeContext{outer: e.rangeContext}
+ }
c0 := e.escapeList(c, n.List)
- if nodeName == "range" && c0.state != stateError {
+ if nodeName == "range" {
+ if c0.state != stateError {
+ c0 = joinRange(c0, e.rangeContext)
+ }
+ e.rangeContext = e.rangeContext.outer
+ if c0.state == stateError {
+ return c0
+ }
+
// The "true" branch of a "range" node can execute multiple times.
// We check that executing n.List once results in the same context
// as executing n.List twice.
+ e.rangeContext = &rangeContext{outer: e.rangeContext}
c1, _ := e.escapeListConditionally(c0, n.List, nil)
c0 = join(c0, c1, n, nodeName)
if c0.state == stateError {
+ e.rangeContext = e.rangeContext.outer
// Make clear that this is a problem on loop re-entry
// since developers tend to overlook that branch when
// debugging templates.
c0.err.Description = "on range loop re-entry: " + c0.err.Description
return c0
}
+ c0 = joinRange(c0, e.rangeContext)
+ e.rangeContext = e.rangeContext.outer
+ if c0.state == stateError {
+ return c0
+ }
}
c1 := e.escapeList(c, n.ElseList)
return join(c0, c1, n, nodeName)
}
+func joinRange(c0 context, rc *rangeContext) context {
+ // Merge contexts at break and continue statements into overall body context.
+ // In theory we could treat breaks differently from continues, but for now it is
+ // enough to treat them both as going back to the start of the loop (which may then stop).
+ for _, c := range rc.breaks {
+ c0 = join(c0, c, c.n, "range")
+ if c0.state == stateError {
+ c0.err.Line = c.n.(*parse.BreakNode).Line
+ c0.err.Description = "at range loop break: " + c0.err.Description
+ return c0
+ }
+ }
+ for _, c := range rc.continues {
+ c0 = join(c0, c, c.n, "range")
+ if c0.state == stateError {
+ c0.err.Line = c.n.(*parse.ContinueNode).Line
+ c0.err.Description = "at range loop continue: " + c0.err.Description
+ return c0
+ }
+ }
+ return c0
+}
+
// escapeList escapes a list template node.
func (e *escaper) escapeList(c context, n *parse.ListNode) context {
if n == nil {
}
for _, m := range n.Nodes {
c = e.escape(c, m)
+ if c.state == stateDead {
+ break
+ }
}
return c
}
// which is the same as whether e was updated.
func (e *escaper) escapeListConditionally(c context, n *parse.ListNode, filter func(*escaper, context) bool) (context, bool) {
e1 := makeEscaper(e.ns)
+ e1.rangeContext = e.rangeContext
// Make type inferences available to f.
for k, v := range e.output {
e1.output[k] = v
"<a href='/foo?{{range .Items}}&{{.K}}={{.V}}{{end}}'>",
"",
},
+ {
+ "{{range .Items}}<a{{if .X}}{{end}}>{{end}}",
+ "",
+ },
+ {
+ "{{range .Items}}<a{{if .X}}{{end}}>{{continue}}{{end}}",
+ "",
+ },
+ {
+ "{{range .Items}}<a{{if .X}}{{end}}>{{break}}{{end}}",
+ "",
+ },
+ {
+ "{{range .Items}}<a{{if .X}}{{end}}>{{if .X}}{{break}}{{end}}{{end}}",
+ "",
+ },
// Error cases.
{
"{{if .Cond}}<a{{end}}",
"\n{{range .Items}} x='<a{{end}}",
"z:2:8: on range loop re-entry: {{range}} branches",
},
+ {
+ "{{range .Items}}<a{{if .X}}{{break}}{{end}}>{{end}}",
+ "z:1:29: at range loop break: {{range}} branches end in different contexts",
+ },
+ {
+ "{{range .Items}}<a{{if .X}}{{continue}}{{end}}>{{end}}",
+ "z:1:29: at range loop continue: {{range}} branches end in different contexts",
+ },
{
"<a b=1 c={{.H}}",
"z: ends in a non-text context: {stateAttr delimSpaceOrTagEnd",
{"range empty no else", "{{range .SIEmpty}}-{{.}}-{{end}}", "", tVal, true},
{"range []int else", "{{range .SI}}-{{.}}-{{else}}EMPTY{{end}}", "-3--4--5-", tVal, true},
{"range empty else", "{{range .SIEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+ {"range []int break else", "{{range .SI}}-{{.}}-{{break}}NOTREACHED{{else}}EMPTY{{end}}", "-3-", tVal, true},
+ {"range []int continue else", "{{range .SI}}-{{.}}-{{continue}}NOTREACHED{{else}}EMPTY{{end}}", "-3--4--5-", tVal, true},
{"range []bool", "{{range .SB}}-{{.}}-{{end}}", "-true--false-", tVal, true},
{"range []int method", "{{range .SI | .MAdd .I}}-{{.}}-{{end}}", "-20--21--22-", tVal, true},
{"range map", "{{range .MSI}}-{{.}}-{{end}}", "-1--3--2-", tVal, true},
T0 is executed; otherwise, dot is set to the successive elements
of the array, slice, or map and T1 is executed.
+ {{break}}
+ The innermost {{range pipeline}} loop is ended early, stopping the
+ current iteration and bypassing all remaining iterations.
+
+ {{continue}}
+ The current iteration of the innermost {{range pipeline}} loop is
+ stopped, and the loop starts the next iteration.
+
{{template "name"}}
The template with the specified name is executed with nil data.
package template
import (
+ "errors"
"fmt"
"internal/fmtsort"
"io"
return b.String()
}
+// Sentinel errors for use with panic to signal early exits from range loops.
+var (
+ walkBreak = errors.New("break")
+ walkContinue = errors.New("continue")
+)
+
// 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) {
if len(node.Pipe.Decl) == 0 {
s.printValue(node, val)
}
+ case *parse.BreakNode:
+ panic(walkBreak)
case *parse.CommentNode:
+ case *parse.ContinueNode:
+ panic(walkContinue)
case *parse.IfNode:
s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
case *parse.ListNode:
func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
s.at(r)
+ defer func() {
+ if r := recover(); r != nil && r != walkBreak {
+ panic(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.
if len(r.Pipe.Decl) > 1 {
s.setTopVar(2, index)
}
+ defer s.pop(mark)
+ defer func() {
+ // Consume panic(walkContinue)
+ if r := recover(); r != nil && r != walkContinue {
+ panic(r)
+ }
+ }()
s.walk(elem, r.List)
- s.pop(mark)
}
switch val.Kind() {
case reflect.Array, reflect.Slice:
{"range empty no else", "{{range .SIEmpty}}-{{.}}-{{end}}", "", tVal, true},
{"range []int else", "{{range .SI}}-{{.}}-{{else}}EMPTY{{end}}", "-3--4--5-", tVal, true},
{"range empty else", "{{range .SIEmpty}}-{{.}}-{{else}}EMPTY{{end}}", "EMPTY", tVal, true},
+ {"range []int break else", "{{range .SI}}-{{.}}-{{break}}NOTREACHED{{else}}EMPTY{{end}}", "-3-", tVal, true},
+ {"range []int continue else", "{{range .SI}}-{{.}}-{{continue}}NOTREACHED{{else}}EMPTY{{end}}", "-3--4--5-", tVal, true},
{"range []bool", "{{range .SB}}-{{.}}-{{end}}", "-true--false-", tVal, true},
{"range []int method", "{{range .SI | .MAdd .I}}-{{.}}-{{end}}", "-20--21--22-", tVal, true},
{"range map", "{{range .MSI}}-{{.}}-{{end}}", "-1--3--2-", tVal, true},
// 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
var key = map[string]itemType{
".": itemDot,
"block": itemBlock,
+ "break": itemBreak,
+ "continue": itemContinue,
"define": itemDefine,
"else": itemElse,
"end": itemEnd,
parenDepth int // nesting depth of ( ) exprs
line int // 1+number of newlines seen
startLine int // start line of this item
+ breakOK bool // break keyword allowed
+ continueOK bool // continue keyword allowed
}
// next returns the next rune in the input.
}
switch {
case key[word] > itemKeyword:
- l.emit(key[word])
+ item := key[word]
+ if item == itemBreak && !l.breakOK || item == itemContinue && !l.continueOK {
+ l.emit(itemIdentifier)
+ } else {
+ l.emit(item)
+ }
case word[0] == '.':
l.emit(itemField)
case word == "true", word == "false":
// keywords
itemDot: ".",
itemBlock: "block",
+ itemBreak: "break",
+ itemContinue: "continue",
itemDefine: "define",
itemElse: "else",
itemIf: "if",
NodeVariable // A $ variable.
NodeWith // A with action.
NodeComment // A comment.
+ NodeBreak // A break action.
+ NodeContinue // A continue action.
)
// Nodes.
return i.tr.newIf(i.Pos, i.Line, i.Pipe.CopyPipe(), i.List.CopyList(), i.ElseList.CopyList())
}
+// BreakNode represents a {{break}} action.
+type BreakNode struct {
+ tr *Tree
+ NodeType
+ Pos
+ Line int
+}
+
+func (t *Tree) newBreak(pos Pos, line int) *BreakNode {
+ return &BreakNode{tr: t, NodeType: NodeBreak, Pos: pos, Line: line}
+}
+
+func (b *BreakNode) Copy() Node { return b.tr.newBreak(b.Pos, b.Line) }
+func (b *BreakNode) String() string { return "{{break}}" }
+func (b *BreakNode) tree() *Tree { return b.tr }
+func (b *BreakNode) writeTo(sb *strings.Builder) { sb.WriteString("{{break}}") }
+
+// ContinueNode represents a {{continue}} action.
+type ContinueNode struct {
+ tr *Tree
+ NodeType
+ Pos
+ Line int
+}
+
+func (t *Tree) newContinue(pos Pos, line int) *ContinueNode {
+ return &ContinueNode{tr: t, NodeType: NodeContinue, Pos: pos, Line: line}
+}
+
+func (c *ContinueNode) Copy() Node { return c.tr.newContinue(c.Pos, c.Line) }
+func (c *ContinueNode) String() string { return "{{continue}}" }
+func (c *ContinueNode) tree() *Tree { return c.tr }
+func (c *ContinueNode) writeTo(sb *strings.Builder) { sb.WriteString("{{continue}}") }
+
// RangeNode represents a {{range}} action and its commands.
type RangeNode struct {
BranchNode
vars []string // variables defined at the moment.
treeSet map[string]*Tree
actionLine int // line of left delim starting action
+ rangeDepth int
mode Mode
}
t.vars = []string{"$"}
t.funcs = funcs
t.treeSet = treeSet
+ lex.breakOK = !t.hasFunction("break")
+ lex.continueOK = !t.hasFunction("continue")
}
// stopParse terminates parsing.
switch token := t.nextNonSpace(); token.typ {
case itemBlock:
return t.blockControl()
+ case itemBreak:
+ return t.breakControl(token.pos, token.line)
+ case itemContinue:
+ return t.continueControl(token.pos, token.line)
case itemElse:
return t.elseControl()
case itemEnd:
return t.newAction(token.pos, token.line, t.pipeline("command", itemRightDelim))
}
+// Break:
+// {{break}}
+// Break keyword is past.
+func (t *Tree) breakControl(pos Pos, line int) Node {
+ if token := t.next(); token.typ != itemRightDelim {
+ t.unexpected(token, "in {{break}}")
+ }
+ if t.rangeDepth == 0 {
+ t.errorf("{{break}} outside {{range}}")
+ }
+ return t.newBreak(pos, line)
+}
+
+// Continue:
+// {{continue}}
+// Continue keyword is past.
+func (t *Tree) continueControl(pos Pos, line int) Node {
+ if token := t.next(); token.typ != itemRightDelim {
+ t.unexpected(token, "in {{continue}}")
+ }
+ if t.rangeDepth == 0 {
+ t.errorf("{{continue}} outside {{range}}")
+ }
+ return t.newContinue(pos, line)
+}
+
// Pipeline:
// declarations? command ('|' command)*
func (t *Tree) pipeline(context string, end itemType) (pipe *PipeNode) {
func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
defer t.popVars(len(t.vars))
pipe = t.pipeline(context, itemRightDelim)
+ if context == "range" {
+ t.rangeDepth++
+ }
var next Node
list, next = t.itemList()
+ if context == "range" {
+ t.rangeDepth--
+ }
switch next.Type() {
case nodeEnd: //done
case nodeElse:
// {{range pipeline}} itemList {{else}} itemList {{end}}
// Range keyword is past.
func (t *Tree) rangeControl() Node {
- return t.newRange(t.parseControl(false, "range"))
+ r := t.newRange(t.parseControl(false, "range"))
+ return r
}
// With:
`{{range $x := .SI}}{{.}}{{end}}`},
{"range 2 vars", "{{range $x, $y := .SI}}{{.}}{{end}}", noError,
`{{range $x, $y := .SI}}{{.}}{{end}}`},
+ {"range with break", "{{range .SI}}{{.}}{{break}}{{end}}", noError,
+ `{{range .SI}}{{.}}{{break}}{{end}}`},
+ {"range with continue", "{{range .SI}}{{.}}{{continue}}{{end}}", noError,
+ `{{range .SI}}{{.}}{{continue}}{{end}}`},
{"constants", "{{range .SI 1 -3.2i true false 'a' nil}}{{end}}", noError,
`{{range .SI 1 -3.2i true false 'a' nil}}{{end}}`},
{"template", "{{template `x`}}", noError,
{"adjacent args", "{{printf 3`x`}}", hasError, ""},
{"adjacent args with .", "{{printf `x`.}}", hasError, ""},
{"extra end after if", "{{if .X}}a{{else if .Y}}b{{end}}{{end}}", hasError, ""},
+ {"break outside range", "{{range .}}{{end}} {{break}}", hasError, ""},
+ {"continue outside range", "{{range .}}{{end}} {{continue}}", hasError, ""},
+ {"break in range else", "{{range .}}{{else}}{{break}}{{end}}", hasError, ""},
+ {"continue in range else", "{{range .}}{{else}}{{continue}}{{end}}", hasError, ""},
// Other kinds of assignments and operators aren't available yet.
{"bug0a", "{{$x := 0}}{{$x}}", noError, "{{$x := 0}}{{$x}}"},
{"bug0b", "{{$x += 1}}{{$x}}", hasError, ""},