template: better error message for empty templates

New("x").ParseFiles("y") can result in an empty "x" template.
Make the message clearer that this is the problem. The error
returns from both template packages in this case were
confusing.

I considered making the method use "x" instead of "y" in
this case, but that just made other situations confusing
and harder to explain.

Fixes #2594.

R=golang-dev, rsc, r
CC=golang-dev
https://golang.org/cl/5498048

diff --git a/src/pkg/html/template/escape.go b/src/pkg/html/template/escape.go
index 2f6be3b6c21feee57319a5d3a7436635fdc4c7b6..c6f723ae4a47baff517340b075fca9286d090005 100644 (file)
--- a/src/pkg/html/template/escape.go
+++ b/src/pkg/html/template/escape.go
@@ -486,9 +486,17 @@ func (e *escaper) escapeTree(c context, name string, line int) (context, string)
        }
        t := e.template(name)
        if t == nil {
+               // Two cases: The template exists but is empty, or has never been mentioned at
+               // all. Distinguish the cases in the error messages.
+               if e.tmpl.set[name] != nil {
+                       return context{
+                               state: stateError,
+                               err:   errorf(ErrNoSuchTemplate, line, "%q is an incomplete or empty template", name),
+                       }, dname
+               }
                return context{
                        state: stateError,
-                       err:   errorf(ErrNoSuchTemplate, line, "no such template %s", name),
+                       err:   errorf(ErrNoSuchTemplate, line, "no such template %q", name),
                }, dname
        }
        if dname != name {

diff --git a/src/pkg/html/template/escape_test.go b/src/pkg/html/template/escape_test.go
index 7702300ffda4d09f9b335ce9d7d341f907986ba6..a57f9826b5b5a4e75a5214cc1bf039ed04228082 100644 (file)
--- a/src/pkg/html/template/escape_test.go
+++ b/src/pkg/html/template/escape_test.go
@@ -928,7 +928,7 @@ func TestErrors(t *testing.T) {
                },
                {
                        `{{template "foo"}}`,
-                       "z:1: no such template foo",
+                       "z:1: no such template \"foo\"",
                },
                {
                        `<div{{template "y"}}>` +

diff --git a/src/pkg/text/template/exec.go b/src/pkg/text/template/exec.go
index ba20fff89dfbdf4dbe39381c7697dba924f662bb..acb88afee3684afa1e1bfb4222277ac7664d2285 100644 (file)
--- a/src/pkg/text/template/exec.go
+++ b/src/pkg/text/template/exec.go
@@ -107,7 +107,7 @@ func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
                vars: []variable{{"$", value}},
        }
        if t.Tree == nil || t.Root == nil {
-               state.errorf("must be parsed before execution")
+               state.errorf("%q is an incomplete or empty template", t.name)
        }
        state.walk(value, t.Root)
        return