Fix panic when unmarshaling datetime values to incompatible types (#1028) (#1029)

pelletier · claude · web-flow · commit 2edc61f17159 · 2026-01-23T22:04:40.000-05:00
Return a type mismatch error instead of panicking when datetime values (DateTime, LocalDate, LocalTime, LocalDateTime) are unmarshaled into incompatible Go types. This makes the decoder safer for processing untrusted TOML input. https://claude.ai/code/session_011jwvtDS5M2KncLrqJpgMr5 Co-authored-by: Claude <noreply@anthropic.com>
diff --git a/unmarshaler.go b/unmarshaler.go
@@ -852,6 +852,9 @@ func (d *decoder) unmarshalDateTime(value *unstable.Node, v reflect.Value) error
 		return err
 	}
 
+	if v.Kind() != reflect.Interface && v.Type() != timeType {
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("datetime", v.Type()))
+	}
 	v.Set(reflect.ValueOf(dt))
 	return nil
 }
@@ -862,14 +865,14 @@ func (d *decoder) unmarshalLocalDate(value *unstable.Node, v reflect.Value) erro
 		return err
 	}
 
+	if v.Kind() != reflect.Interface && v.Type() != timeType {
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local date", v.Type()))
+	}
 	if v.Type() == timeType {
-		cast := ld.AsTime(time.Local)
-		v.Set(reflect.ValueOf(cast))
+		v.Set(reflect.ValueOf(ld.AsTime(time.Local)))
 		return nil
 	}
-
 	v.Set(reflect.ValueOf(ld))
-
 	return nil
 }
 
@@ -883,6 +886,9 @@ func (d *decoder) unmarshalLocalTime(value *unstable.Node, v reflect.Value) erro
 		return unstable.NewParserError(rest, "extra characters at the end of a local time")
 	}
 
+	if v.Kind() != reflect.Interface {
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local time", v.Type()))
+	}
 	v.Set(reflect.ValueOf(lt))
 	return nil
 }
@@ -897,15 +903,14 @@ func (d *decoder) unmarshalLocalDateTime(value *unstable.Node, v reflect.Value)
 		return unstable.NewParserError(rest, "extra characters at the end of a local date time")
 	}
 
+	if v.Kind() != reflect.Interface && v.Type() != timeType {
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local datetime", v.Type()))
+	}
 	if v.Type() == timeType {
-		cast := ldt.AsTime(time.Local)
-
-		v.Set(reflect.ValueOf(cast))
+		v.Set(reflect.ValueOf(ldt.AsTime(time.Local)))
 		return nil
 	}
-
 	v.Set(reflect.ValueOf(ldt))
-
 	return nil
 }
 
diff --git a/unmarshaler_test.go b/unmarshaler_test.go
@@ -4344,3 +4344,44 @@ value = "b"
 		},
 	}, cfg)
 }
+
+func TestIssue1028(t *testing.T) {
+	// Datetime values assigned to incompatible types should return an error,
+	// not panic.
+
+	type Item struct {
+		Name string `toml:"name"`
+	}
+
+	type Config struct {
+		Items map[string]Item `toml:"items"`
+	}
+
+	// Error: "cannot decode TOML datetime into struct field Config.Items of type map[string]Item"
+	t.Run("OffsetDateTime", func(t *testing.T) {
+		var c Config
+		err := toml.Unmarshal([]byte(`items = 2023-01-01T10:20:30Z`), &c)
+		assert.Error(t, err)
+	})
+
+	// Error: "cannot decode TOML local datetime into struct field Config.Items of type map[string]Item"
+	t.Run("LocalDateTime", func(t *testing.T) {
+		var c Config
+		err := toml.Unmarshal([]byte(`items = 2023-01-01T10:20:30`), &c)
+		assert.Error(t, err)
+	})
+
+	// Error: "cannot decode TOML local date into struct field Config.Items of type map[string]Item"
+	t.Run("LocalDate", func(t *testing.T) {
+		var c Config
+		err := toml.Unmarshal([]byte(`items = 2023-01-01`), &c)
+		assert.Error(t, err)
+	})
+
+	// Error: "cannot decode TOML local time into struct field Config.Items of type map[string]Item"
+	t.Run("LocalTime", func(t *testing.T) {
+		var c Config
+		err := toml.Unmarshal([]byte(`items = 10:20:30`), &c)
+		assert.Error(t, err)
+	})
+}

Original file line number	Diff line number	Diff line change
`@@ -852,6 +852,9 @@ func (d decoder) unmarshalDateTime(value unstable.Node, v reflect.Value) error`
`852`	`852`	`return err`
`853`	`853`	`}`
`854`	`854`
	`855`	`+ if v.Kind() != reflect.Interface && v.Type() != timeType {`
	`856`	`+ return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("datetime", v.Type()))`
	`857`	`+ }`
`855`	`858`	`v.Set(reflect.ValueOf(dt))`
`856`	`859`	`return nil`
`857`	`860`	`}`
`@@ -862,14 +865,14 @@ func (d decoder) unmarshalLocalDate(value unstable.Node, v reflect.Value) erro`
`862`	`865`	`return err`
`863`	`866`	`}`
`864`	`867`
	`868`	`+ if v.Kind() != reflect.Interface && v.Type() != timeType {`
	`869`	`+ return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local date", v.Type()))`
	`870`	`+ }`
`865`	`871`	`if v.Type() == timeType {`
`866`		`- cast := ld.AsTime(time.Local)`
`867`		`- v.Set(reflect.ValueOf(cast))`
	`872`	`+ v.Set(reflect.ValueOf(ld.AsTime(time.Local)))`
`868`	`873`	`return nil`
`869`	`874`	`}`
`870`		`-`
`871`	`875`	`v.Set(reflect.ValueOf(ld))`
`872`		`-`
`873`	`876`	`return nil`
`874`	`877`	`}`
`875`	`878`
`@@ -883,6 +886,9 @@ func (d decoder) unmarshalLocalTime(value unstable.Node, v reflect.Value) erro`
`883`	`886`	`return unstable.NewParserError(rest, "extra characters at the end of a local time")`
`884`	`887`	`}`
`885`	`888`
	`889`	`+ if v.Kind() != reflect.Interface {`
	`890`	`+ return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local time", v.Type()))`
	`891`	`+ }`
`886`	`892`	`v.Set(reflect.ValueOf(lt))`
`887`	`893`	`return nil`
`888`	`894`	`}`
`@@ -897,15 +903,14 @@ func (d decoder) unmarshalLocalDateTime(value unstable.Node, v reflect.Value)`
`897`	`903`	`return unstable.NewParserError(rest, "extra characters at the end of a local date time")`
`898`	`904`	`}`
`899`	`905`
	`906`	`+ if v.Kind() != reflect.Interface && v.Type() != timeType {`
	`907`	`+ return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local datetime", v.Type()))`
	`908`	`+ }`
`900`	`909`	`if v.Type() == timeType {`
`901`		`- cast := ldt.AsTime(time.Local)`
`902`		`-`
`903`		`- v.Set(reflect.ValueOf(cast))`
	`910`	`+ v.Set(reflect.ValueOf(ldt.AsTime(time.Local)))`
`904`	`911`	`return nil`
`905`	`912`	`}`
`906`		`-`
`907`	`913`	`v.Set(reflect.ValueOf(ldt))`
`908`		`-`
`909`	`914`	`return nil`
`910`	`915`	`}`
`911`	`916`