text/template: clarify error when too few or too many return values

Prior to CL 561115, calling a function without any return values would
print "function called with 0 args; should be 1 or 2". Afterwards, the
error message became "too many return values".

Keep the improvement of referring to return values rather than args,
and bring back clarity about their actual and permitted numbers.

Change-Id: I2c014e4633208cc7052fac265a995a8f2fe68151
Reviewed-on: https://go-review.googlesource.com/c/go/+/588355
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index 4ec213d8cfb24d6ca5890a11e4daaed701c0e185..9903e17d0ef2c82e02bc1eedb0583117c75abde5 100644 (file)
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -81,7 +81,8 @@ type T struct {
        NilOKFunc              func(*int) bool
        ErrFunc                func() (string, error)
        PanicFunc              func() string
-       InvalidReturnCountFunc func() (string, error, int)
+       TooFewReturnCountFunc  func()
+       TooManyReturnCountFunc func() (string, error, int)
        InvalidReturnTypeFunc  func() (string, bool)
        // Template to test evaluation of templates.
        Tmpl *Template
@@ -170,7 +171,8 @@ var tVal = &T{
        NilOKFunc:                 func(s *int) bool { return s == nil },
        ErrFunc:                   func() (string, error) { return "bla", nil },
        PanicFunc:                 func() string { panic("test panic") },
-       InvalidReturnCountFunc:    func() (string, error, int) { return "", nil, 0 },
+       TooFewReturnCountFunc:     func() {},
+       TooManyReturnCountFunc:    func() (string, error, int) { return "", nil, 0 },
        InvalidReturnTypeFunc:     func() (string, bool) { return "", false },
        Tmpl:                      Must(New("x").Parse("test template")), // "x" is the value of .X
 }
@@ -1746,16 +1748,22 @@ func TestFunctionCheckDuringCall(t *testing.T) {
                        wantErr: "error calling call: wrong number of args for .VariadicFuncInt: got 0 want at least 1",
                },
                {
-                       name:    "call invalid return number func",
-                       input:   `{{call .InvalidReturnCountFunc}}`,
+                       name:    "call too few return number func",
+                       input:   `{{call .TooFewReturnCountFunc}}`,
                        data:    tVal,
-                       wantErr: "error calling call: too many return values for .InvalidReturnCountFunc",
+                       wantErr: "error calling call: function .TooFewReturnCountFunc has 0 return values; should be 1 or 2",
+               },
+               {
+                       name:    "call too many return number func",
+                       input:   `{{call .TooManyReturnCountFunc}}`,
+                       data:    tVal,
+                       wantErr: "error calling call: function .TooManyReturnCountFunc has 3 return values; should be 1 or 2",
                },
                {
                        name:    "call invalid return type func",
                        input:   `{{call .InvalidReturnTypeFunc}}`,
                        data:    tVal,
-                       wantErr: "error calling call: invalid function signature for .InvalidReturnTypeFunc: second argument should be error; is bool",
+                       wantErr: "error calling call: invalid function signature for .InvalidReturnTypeFunc: second return value should be error; is bool",
                },
                {
                        name:    "call pipeline",

diff --git a/src/text/template/funcs.go b/src/text/template/funcs.go
index 6832ae3682deb7603a85952d5a390de5c1352ddc..7d63cf8b7bb6db3864672e162394d21d6090b83b 100644 (file)
--- a/src/text/template/funcs.go
+++ b/src/text/template/funcs.go
@@ -110,18 +110,16 @@ func addFuncs(out, in FuncMap) {
 
 // goodFunc reports whether the function or method has the right result signature.
 func goodFunc(name string, typ reflect.Type) error {
-       numOut := typ.NumOut()
-
        // We allow functions with 1 result or 2 results where the second is an error.
-       switch {
+       switch numOut := typ.NumOut(); {
        case numOut == 1:
                return nil
        case numOut == 2 && typ.Out(1) == errorType:
                return nil
        case numOut == 2:
-               return fmt.Errorf("invalid function signature for %s: second argument should be error; is %s", name, typ.Out(1))
+               return fmt.Errorf("invalid function signature for %s: second return value should be error; is %s", name, typ.Out(1))
        default:
-               return fmt.Errorf("too many return values for %s", name)
+               return fmt.Errorf("function %s has %d return values; should be 1 or 2", name, typ.NumOut())
        }
 }