Fix error handling for the time func alias

Fixes #8835

53 files changed, 122 insertions, 65 deletions

diff --git a/hugolib/dates_test.go b/hugolib/dates_test.go
index dfcb681a3..4b4dc29d2 100644
--- a/hugolib/dates_test.go
+++ b/hugolib/dates_test.go
@@ -203,3 +203,14 @@ timeZone = "America/LosAngeles"   # Should be America/Los_Angeles
 	b.Assert(err, qt.Not(qt.IsNil))
 	b.Assert(err.Error(), qt.Contains, `failed to load config: invalid timeZone for language "en": unknown time zone America/LosAngeles`)
 }
+
+// Issue 8835
+func TestTimeOnError(t *testing.T) {
+	b := newTestSitesBuilder(t)
+
+	b.WithTemplates("index.html", `time: {{ time "2020-10-20" "invalid-timezone" }}`)
+	b.WithContent("p1.md", "")
+
+	b.Assert(b.BuildE(BuildCfg{}), qt.Not(qt.IsNil))
+
+}
diff --git a/tpl/cast/init.go b/tpl/cast/init.go
index 3f1f3f253..079be4719 100644
--- a/tpl/cast/init.go
+++ b/tpl/cast/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.ToInt,
diff --git a/tpl/cast/init_test.go b/tpl/cast/init_test.go
index dd024b775..5eb4a9086 100644
--- a/tpl/cast/init_test.go
+++ b/tpl/cast/init_test.go
@@ -37,5 +37,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/collections/init.go b/tpl/collections/init.go
index 4126b4410..dc4e1ff31 100644
--- a/tpl/collections/init.go
+++ b/tpl/collections/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.After,
diff --git a/tpl/collections/init_test.go b/tpl/collections/init_test.go
index 3a3b2070f..570e58d93 100644
--- a/tpl/collections/init_test.go
+++ b/tpl/collections/init_test.go
@@ -37,5 +37,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/compare/init.go b/tpl/compare/init.go
index f96e382e5..9aa533f55 100644
--- a/tpl/compare/init.go
+++ b/tpl/compare/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Default,
diff --git a/tpl/compare/init_test.go b/tpl/compare/init_test.go
index 29a525f93..8698cb5e3 100644
--- a/tpl/compare/init_test.go
+++ b/tpl/compare/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/crypto/init.go b/tpl/crypto/init.go
index 2c6e94298..5ce2a4b5e 100644
--- a/tpl/crypto/init.go
+++ b/tpl/crypto/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.MD5,
diff --git a/tpl/crypto/init_test.go b/tpl/crypto/init_test.go
index 120e1e4e7..1c200d777 100644
--- a/tpl/crypto/init_test.go
+++ b/tpl/crypto/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/data/init.go b/tpl/data/init.go
index 3bdc02786..5ac24eaab 100644
--- a/tpl/data/init.go
+++ b/tpl/data/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.GetCSV,
diff --git a/tpl/data/init_test.go b/tpl/data/init_test.go
index 9174d42a6..631a91b39 100644
--- a/tpl/data/init_test.go
+++ b/tpl/data/init_test.go
@@ -41,5 +41,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/debug/init.go b/tpl/debug/init.go
index e478fb46d..1f032ce69 100644
--- a/tpl/debug/init.go
+++ b/tpl/debug/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Dump,
diff --git a/tpl/debug/init_test.go b/tpl/debug/init_test.go
index 35c6a193e..226915b34 100644
--- a/tpl/debug/init_test.go
+++ b/tpl/debug/init_test.go
@@ -38,5 +38,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/encoding/init.go b/tpl/encoding/init.go
index f97b17182..77c9c8c49 100644
--- a/tpl/encoding/init.go
+++ b/tpl/encoding/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Base64Decode,
diff --git a/tpl/encoding/init_test.go b/tpl/encoding/init_test.go
index 5fd71eb32..666a4e549 100644
--- a/tpl/encoding/init_test.go
+++ b/tpl/encoding/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/fmt/init.go b/tpl/fmt/init.go
index f322f5117..c02f985be 100644
--- a/tpl/fmt/init.go
+++ b/tpl/fmt/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Print,
diff --git a/tpl/fmt/init_test.go b/tpl/fmt/init_test.go
index 8fa3945b8..07b740a73 100644
--- a/tpl/fmt/init_test.go
+++ b/tpl/fmt/init_test.go
@@ -38,5 +38,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/hugo/init.go b/tpl/hugo/init.go
index c57d4a27a..f2c43893e 100644
--- a/tpl/hugo/init.go
+++ b/tpl/hugo/init.go
@@ -27,7 +27,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return h },
+			Context: func(args ...interface{}) (interface{}, error) { return h, nil },
 		}
 
 		// We just add the Hugo struct as the namespace here. No method mappings.
diff --git a/tpl/hugo/init_test.go b/tpl/hugo/init_test.go
index 9b1b14be4..bc806448e 100644
--- a/tpl/hugo/init_test.go
+++ b/tpl/hugo/init_test.go
@@ -43,5 +43,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, s.Hugo())
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, s.Hugo())
 }
diff --git a/tpl/images/init.go b/tpl/images/init.go
index e9fd52e73..f3233f6e9 100644
--- a/tpl/images/init.go
+++ b/tpl/images/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Config,
diff --git a/tpl/images/init_test.go b/tpl/images/init_test.go
index d6dc26fe7..d8d8d7839 100644
--- a/tpl/images/init_test.go
+++ b/tpl/images/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/inflect/init.go b/tpl/inflect/init.go
index 52b234df3..548827465 100644
--- a/tpl/inflect/init.go
+++ b/tpl/inflect/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Humanize,
diff --git a/tpl/inflect/init_test.go b/tpl/inflect/init_test.go
index 322813b5f..38499838c 100644
--- a/tpl/inflect/init_test.go
+++ b/tpl/inflect/init_test.go
@@ -37,5 +37,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/internal/templatefuncsRegistry.go b/tpl/internal/templatefuncsRegistry.go
index 6d58d8d2b..df300a5bb 100644
--- a/tpl/internal/templatefuncsRegistry.go
+++ b/tpl/internal/templatefuncsRegistry.go
@@ -49,7 +49,7 @@ type TemplateFuncsNamespace struct {
 	Name string
 
 	// This is the method receiver.
-	Context func(v ...interface{}) interface{}
+	Context func(v ...interface{}) (interface{}, error)
 
 	// Additional info, aliases and examples, per method name.
 	MethodMappings map[string]TemplateFuncMethodMapping
@@ -172,7 +172,10 @@ func (t *TemplateFuncsNamespace) toJSON() ([]byte, error) {
 
 	buf.WriteString(fmt.Sprintf(`%q: {`, t.Name))
 
-	ctx := t.Context()
+	ctx, err := t.Context()
+	if err != nil {
+		return nil, err
+	}
 	ctxType := reflect.TypeOf(ctx)
 	for i := 0; i < ctxType.NumMethod(); i++ {
 		method := ctxType.Method(i)
diff --git a/tpl/js/init.go b/tpl/js/init.go
index 0af10bb10..4ab8671cc 100644
--- a/tpl/js/init.go
+++ b/tpl/js/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		return ns
diff --git a/tpl/lang/init.go b/tpl/lang/init.go
index beb148ff6..f74b6fc35 100644
--- a/tpl/lang/init.go
+++ b/tpl/lang/init.go
@@ -27,7 +27,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Translate,
diff --git a/tpl/lang/init_test.go b/tpl/lang/init_test.go
index 61d7b5047..e62db95b9 100644
--- a/tpl/lang/init_test.go
+++ b/tpl/lang/init_test.go
@@ -42,5 +42,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/math/init.go b/tpl/math/init.go
index 4d8a23fde..32315d362 100644
--- a/tpl/math/init.go
+++ b/tpl/math/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Add,
diff --git a/tpl/math/init_test.go b/tpl/math/init_test.go
index 6c0ce0a93..9998eaf90 100644
--- a/tpl/math/init_test.go
+++ b/tpl/math/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/openapi/openapi3/init.go b/tpl/openapi/openapi3/init.go
index 4b4396ff4..a0084d503 100644
--- a/tpl/openapi/openapi3/init.go
+++ b/tpl/openapi/openapi3/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Unmarshal,
diff --git a/tpl/os/init.go b/tpl/os/init.go
index 9d9b75473..c25d63d56 100644
--- a/tpl/os/init.go
+++ b/tpl/os/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Getenv,
diff --git a/tpl/os/init_test.go b/tpl/os/init_test.go
index 6a91c743a..5d756bab2 100644
--- a/tpl/os/init_test.go
+++ b/tpl/os/init_test.go
@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/partials/init.go b/tpl/partials/init.go
index 4666fa336..d6670d99e 100644
--- a/tpl/partials/init.go
+++ b/tpl/partials/init.go
@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Include,
diff --git a/tpl/partials/init_test.go b/tpl/partials/init_test.go
index 6fd0b3e6d..467e202d4 100644
--- a/tpl/partials/init_test.go
+++ b/tpl/partials/init_test.go
@@ -40,5 +40,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }
diff --git a/tpl/path/init.go b/tpl/path/init.go
index a7f65073c..07f20d717 100644
--- a/tpl/path/init.go
+++ b/tpl/path/init.go
@@ -29,7 +29,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface