text/template: allow {{else if ... }} to simplify if chains
The method is simple: the parser just parses
{{if A}}a{{else if B}}b{{end}}
to the same tree that would be produced by
{{if A}}a{{else}}{{if B}}b{{end}}{{end}}
Thus no changes are required in text/template itself
or in html/template, only in text/template/parse.
Fixes #6085
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/13327043
diff --git a/src/pkg/text/template/doc.go b/src/pkg/text/template/doc.go
index b952789..ab18f9a 100644
--- a/src/pkg/text/template/doc.go
+++ b/src/pkg/text/template/doc.go
@@ -63,6 +63,12 @@
If the value of the pipeline is empty, T0 is executed;
otherwise, T1 is executed. Dot is unaffected.
+ {{if pipeline}} T1 {{else if pipeline}} T0 {{end}}
+ To simplify the appearance of if-else chains, the else action
+ of an if may include another if directly; the effect is exactly
+ the same as writing
+ {{if pipeline}} T1 {{else}}{{if pipeline}} T0 {{end}}{{end}}
+
{{range pipeline}} T1 {{end}}
The value of the pipeline must be an array, slice, map, or channel.
If the value of the pipeline has length zero, nothing is output;
diff --git a/src/pkg/text/template/exec_test.go b/src/pkg/text/template/exec_test.go
index be1a2d2..bc8aee6 100644
--- a/src/pkg/text/template/exec_test.go
+++ b/src/pkg/text/template/exec_test.go
@@ -374,6 +374,8 @@
{"if map not unset", "{{if not .MXI.none}}ZERO{{else}}NON-ZERO{{end}}", "ZERO", tVal, true},
{"if $x with $y int", "{{if $x := true}}{{with $y := .I}}{{$x}},{{$y}}{{end}}{{end}}", "true,17", tVal, true},
{"if $x with $x int", "{{if $x := true}}{{with $x := .I}}{{$x}},{{end}}{{$x}}{{end}}", "17,true", tVal, true},
+ {"if else if", "{{if false}}FALSE{{else if true}}TRUE{{end}}", "TRUE", tVal, true},
+ {"if else chain", "{{if eq 1 3}}1{{else if eq 2 3}}2{{else if eq 3 3}}3{{end}}", "3", tVal, true},
// Print etc.
{"print", `{{print "hello, print"}}`, "hello, print", tVal, true},
diff --git a/src/pkg/text/template/parse/parse.go b/src/pkg/text/template/parse/parse.go
index 2919124..be83e77 100644
--- a/src/pkg/text/template/parse/parse.go
+++ b/src/pkg/text/template/parse/parse.go
@@ -409,7 +409,7 @@
}
}
-func (t *Tree) parseControl(context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
+func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
defer t.popVars(len(t.vars))
line = t.lex.lineNumber()
pipe = t.pipeline(context)
@@ -418,6 +418,23 @@
switch next.Type() {
case nodeEnd: //done
case nodeElse:
+ if allowElseIf {
+ // Special case for "else if". If the "else" is followed immediately by an "if",
+ // the elseControl will have left the "if" token pending. Treat
+ // {{if a}}_{{else if b}}_{{end}}
+ // as
+ // {{if a}}_{{else}}{{if b}}_{{end}}{{end}}.
+ // To do this, parse the if as usual and stop at it {{end}}; the subsequent{{end}}
+ // is assumed. This technique works even for long if-else-if chains.
+ // TODO: Should we allow else-if in with and range?
+ if t.peek().typ == itemIf {
+ t.next() // Consume the "if" token.
+ elseList = newList(next.Position())
+ elseList.append(t.ifControl())
+ // Do not consume the next item - only one {{end}} required.
+ break
+ }
+ }
elseList, next = t.itemList()
if next.Type() != nodeEnd {
t.errorf("expected end; found %s", next)
@@ -431,7 +448,7 @@
// {{if pipeline}} itemList {{else}} itemList {{end}}
// If keyword is past.
func (t *Tree) ifControl() Node {
- return newIf(t.parseControl("if"))
+ return newIf(t.parseControl(true, "if"))
}
// Range:
@@ -439,7 +456,7 @@
// {{range pipeline}} itemList {{else}} itemList {{end}}
// Range keyword is past.
func (t *Tree) rangeControl() Node {
- return newRange(t.parseControl("range"))
+ return newRange(t.parseControl(false, "range"))
}
// With:
@@ -447,7 +464,7 @@
// {{with pipeline}} itemList {{else}} itemList {{end}}
// If keyword is past.
func (t *Tree) withControl() Node {
- return newWith(t.parseControl("with"))
+ return newWith(t.parseControl(false, "with"))
}
// End:
@@ -461,6 +478,12 @@
// {{else}}
// Else keyword is past.
func (t *Tree) elseControl() Node {
+ // Special case for "else if".
+ peek := t.peekNonSpace()
+ if peek.typ == itemIf {
+ // We see "{{else if ... " but in effect rewrite it to {{else}}{{if ... ".
+ return newElse(peek.pos, t.lex.lineNumber())
+ }
return newElse(t.expect(itemRightDelim, "else").pos, t.lex.lineNumber())
}
diff --git a/src/pkg/text/template/parse/parse_test.go b/src/pkg/text/template/parse/parse_test.go
index 0e5c144..c35f4ac 100644
--- a/src/pkg/text/template/parse/parse_test.go
+++ b/src/pkg/text/template/parse/parse_test.go
@@ -194,6 +194,10 @@
`{{if .X}}"hello"{{end}}`},
{"if with else", "{{if .X}}true{{else}}false{{end}}", noError,
`{{if .X}}"true"{{else}}"false"{{end}}`},
+ {"if with else if", "{{if .X}}true{{else if .Y}}false{{end}}", noError,
+ `{{if .X}}"true"{{else}}{{if .Y}}"false"{{end}}{{end}}`},
+ {"if else chain", "+{{if .X}}X{{else if .Y}}Y{{else if .Z}}Z{{end}}+", noError,
+ `"+"{{if .X}}"X"{{else}}{{if .Y}}"Y"{{else}}{{if .Z}}"Z"{{end}}{{end}}{{end}}"+"`},
{"simple range", "{{range .X}}hello{{end}}", noError,
`{{range .X}}"hello"{{end}}`},
{"chained field range", "{{range .X.Y.Z}}hello{{end}}", noError,
@@ -238,6 +242,7 @@
{"dot applied to parentheses", "{{printf (printf .).}}", hasError, ""},
{"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, ""},
// Equals (and other chars) do not assignments make (yet).
{"bug0a", "{{$x := 0}}{{$x}}", noError, "{{$x := 0}}{{$x}}"},
{"bug0b", "{{$x = 1}}{{$x}}", hasError, ""},
