text/template: add "else with" action

Add "else with" action will reduce the template complexity in some use cases(#57646).
This action will be added:
  {{with pipeline}} T1 {{else with pipeline}} T0 {{end}}.

Fixes #57646

Change-Id: I90ed546ab671805f753343b00bd3c9d1a1d5581d
Reviewed-on: https://go-review.googlesource.com/c/go/+/545376
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

diff --git a/src/html/template/exec_test.go b/src/html/template/exec_test.go
index 05302156e0703390ef1460c000c132be74a29b9b..f60308e6799650618f311e404c601e087fbb403b 100644 (file)
--- a/src/html/template/exec_test.go
+++ b/src/html/template/exec_test.go
@@ -561,6 +561,8 @@ var execTests = []execTest{
        {"with $x struct.U.V", "{{with $x := $}}{{$x.U.V}}{{end}}", "v", tVal, true},
        {"with variable and action", "{{with $x := $}}{{$y := $.U.V}}{{$y}}{{end}}", "v", tVal, true},
        {"with on typed nil interface value", "{{with .NonEmptyInterfaceTypedNil}}TRUE{{ end }}", "", tVal, true},
+       {"with else with", "{{with 0}}{{.}}{{else with true}}{{.}}{{end}}", "true", tVal, true},
+       {"with else with chain", "{{with 0}}{{.}}{{else with false}}{{.}}{{else with `notempty`}}{{.}}{{end}}", "notempty", tVal, true},
 
        // Range.
        {"range []int", "{{range .SI}}-{{.}}-{{end}}", "-3--4--5-", tVal, true},

diff --git a/src/text/template/doc.go b/src/text/template/doc.go
index 032784bc3f0c08fc8c69363198cbf71381556edc..b3ffaabb153c9deac544aa00405321b2f340600e 100644 (file)
--- a/src/text/template/doc.go
+++ b/src/text/template/doc.go
@@ -144,6 +144,13 @@ data, defined in detail in the corresponding sections that follow.
                is executed; otherwise, dot is set to the value of the pipeline
                and T1 is executed.
 
+       {{with pipeline}} T1 {{else with pipeline}} T0 {{end}}
+               To simplify the appearance of with-else chains, the else action
+               of a with may include another with directly; the effect is exactly
+               the same as writing
+                       {{with pipeline}} T1 {{else}}{{with pipeline}} T0 {{end}}{{end}}
+
+
 Arguments
 
 An argument is a simple value, denoted by one of the following.

diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index e607fd3beea86bfbba5302a07f050e2907bc08a7..8fdd9280f2436ff3abf90bab80cc6fbded248f1a 100644 (file)
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -569,6 +569,8 @@ var execTests = []execTest{
        {"with $x struct.U.V", "{{with $x := $}}{{$x.U.V}}{{end}}", "v", tVal, true},
        {"with variable and action", "{{with $x := $}}{{$y := $.U.V}}{{$y}}{{end}}", "v", tVal, true},
        {"with on typed nil interface value", "{{with .NonEmptyInterfaceTypedNil}}TRUE{{ end }}", "", tVal, true},
+       {"with else with", "{{with 0}}{{.}}{{else with true}}{{.}}{{end}}", "true", tVal, true},
+       {"with else with chain", "{{with 0}}{{.}}{{else with false}}{{.}}{{else with `notempty`}}{{.}}{{end}}", "notempty", tVal, true},
 
        // Range.
        {"range []int", "{{range .SI}}-{{.}}-{{end}}", "-3--4--5-", tVal, true},

diff --git a/src/text/template/parse/parse.go b/src/text/template/parse/parse.go
index d43d5334ba04f3c3f7bdbee23378f1155d53a716..b768dd498552ea67ca96fa2670824d2c78352438 100644 (file)
--- a/src/text/template/parse/parse.go
+++ b/src/text/template/parse/parse.go
@@ -521,7 +521,7 @@ func (t *Tree) checkPipeline(pipe *PipeNode, context string) {
        }
 }
 
-func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
+func (t *Tree) parseControl(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" {
@@ -535,27 +535,30 @@ func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int
        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 = t.newList(next.Position())
-                               elseList.append(t.ifControl())
-                               // Do not consume the next item - only one {{end}} required.
-                               break
+               // Special case for "else if" and "else with".
+               // If the "else" is followed immediately by an "if" or "with",
+               // the elseControl will have left the "if" or "with" token pending. Treat
+               //      {{if a}}_{{else if b}}_{{end}}
+               //  {{with a}}_{{else with b}}_{{end}}
+               // as
+               //      {{if a}}_{{else}}{{if b}}_{{end}}{{end}}
+               //  {{with a}}_{{else}}{{with b}}_{{end}}{{end}}.
+               // To do this, parse the "if" or "with" as usual and stop at it {{end}};
+               // the subsequent{{end}} is assumed. This technique works even for long if-else-if chains.
+               if context == "if" && t.peek().typ == itemIf {
+                       t.next() // Consume the "if" token.
+                       elseList = t.newList(next.Position())
+                       elseList.append(t.ifControl())
+               } else if context == "with" && t.peek().typ == itemWith {
+                       t.next()
+                       elseList = t.newList(next.Position())
+                       elseList.append(t.withControl())
+               } else {
+                       elseList, next = t.itemList()
+                       if next.Type() != nodeEnd {
+                               t.errorf("expected end; found %s", next)
                        }
                }
-               elseList, next = t.itemList()
-               if next.Type() != nodeEnd {
-                       t.errorf("expected end; found %s", next)
-               }
        }
        return pipe.Position(), pipe.Line, pipe, list, elseList
 }
@@ -567,7 +570,7 @@ func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int
 //
 // If keyword is past.
 func (t *Tree) ifControl() Node {
-       return t.newIf(t.parseControl(true, "if"))
+       return t.newIf(t.parseControl("if"))
 }
 
 // Range:
@@ -577,7 +580,7 @@ func (t *Tree) ifControl() Node {
 //
 // Range keyword is past.
 func (t *Tree) rangeControl() Node {
-       r := t.newRange(t.parseControl(false, "range"))
+       r := t.newRange(t.parseControl("range"))
        return r
 }
 
@@ -588,7 +591,7 @@ func (t *Tree) rangeControl() Node {
 //
 // If keyword is past.
 func (t *Tree) withControl() Node {
-       return t.newWith(t.parseControl(false, "with"))
+       return t.newWith(t.parseControl("with"))
 }
 
 // End:
@@ -606,10 +609,11 @@ func (t *Tree) endControl() Node {
 //
 // 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 ... ".
+       // The "{{else if ... " and "{{else with ..." will be
+       // treated as "{{else}}{{if ..." and "{{else}}{{with ...".
+       // So return the else node here.
+       if peek.typ == itemIf || peek.typ == itemWith {
                return t.newElse(peek.pos, peek.line)
        }
        token := t.expect(itemRightDelim, "else")

diff --git a/src/text/template/parse/parse_test.go b/src/text/template/parse/parse_test.go
index 59e0a17412235b1c2645543e49e02c0b5ff9827b..faf226d1c3cac26a7ceb4dd8b1d167d38c0d3a96 100644 (file)
--- a/src/text/template/parse/parse_test.go
+++ b/src/text/template/parse/parse_test.go
@@ -244,6 +244,10 @@ var parseTests = []parseTest{
                `{{with .X}}"hello"{{end}}`},
        {"with with else", "{{with .X}}hello{{else}}goodbye{{end}}", noError,
                `{{with .X}}"hello"{{else}}"goodbye"{{end}}`},
+       {"with with else with", "{{with .X}}hello{{else with .Y}}goodbye{{end}}", noError,
+               `{{with .X}}"hello"{{else}}{{with .Y}}"goodbye"{{end}}{{end}}`},
+       {"with else chain", "{{with .X}}X{{else with .Y}}Y{{else with .Z}}Z{{end}}", noError,
+               `{{with .X}}"X"{{else}}{{with .Y}}"Y"{{else}}{{with .Z}}"Z"{{end}}{{end}}{{end}}`},
        // Trimming spaces.
        {"trim left", "x \r\n\t{{- 3}}", noError, `"x"{{3}}`},
        {"trim right", "{{3 -}}\n\n\ty", noError, `{{3}}"y"`},