text/template: provide a mechanism for options
Add one option, which is the motivating example, a way to control
what happens when a map is indexed with a key that is not in the map.
Rather than do something specific for that case, we provide a simple
general option mechanism to avoid adding API if something else
comes up. This general approach also makes it easy for html/template
to track (and adapt, should that become important).
New method: Option(option string...). The option strings are key=value
pairs or just simple strings (no =).
New option:
missingkey: Control the behavior during execution if a map is
indexed with a key that is not present in the map.
"missingkey=default" or "missingkey=invalid"
The default behavior: Do nothing and continue execution.
If printed, the result of the index operation is the string
"<no value>".
"missingkey=zero"
The operation returns the zero value for the map type's element.
"missingkey=error"
Execution stops immediately with an error.
Fixes #6288.
Change-Id: Id811e2b99dc05aff324d517faac113ef3c25293a
Reviewed-on: https://go-review.googlesource.com/8462
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index b1f7787..8c4e165 100644
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -1044,3 +1044,54 @@
}
}
}
+
+func TestMissingMapKey(t *testing.T) {
+ data := map[string]int{
+ "x": 99,
+ }
+ tmpl, err := New("t1").Parse("{{.x}} {{.y}}")
+ if err != nil {
+ t.Fatal(err)
+ }
+ var b bytes.Buffer
+ // By default, just get "<no value>"
+ err = tmpl.Execute(&b, data)
+ if err != nil {
+ t.Fatal(err)
+ }
+ want := "99 <no value>"
+ got := b.String()
+ if got != want {
+ t.Errorf("got %q; expected %q", got, want)
+ }
+ // Same if we set the option explicitly to the default.
+ tmpl.Option("missingkey=default")
+ b.Reset()
+ err = tmpl.Execute(&b, data)
+ if err != nil {
+ t.Fatal("default:", err)
+ }
+ want = "99 <no value>"
+ got = b.String()
+ if got != want {
+ t.Errorf("got %q; expected %q", got, want)
+ }
+ // Next we ask for a zero value
+ tmpl.Option("missingkey=zero")
+ b.Reset()
+ err = tmpl.Execute(&b, data)
+ if err != nil {
+ t.Fatal("zero:", err)
+ }
+ want = "99 0"
+ got = b.String()
+ if got != want {
+ t.Errorf("got %q; expected %q", got, want)
+ }
+ // Now we ask for an error.
+ tmpl.Option("missingkey=error")
+ err = tmpl.Execute(&b, data)
+ if err == nil {
+ t.Errorf("expected error; got none")
+ }
+}
