encoding/json: fix regression in quoted numbers under goexperiment.jsonv2

The legacy parsing of quoted numbers in v1 was according to
the Go grammar for a number, rather than
the JSON grammar for a number.
The former is a superset of the latter.

This is a historical mistake, but usages exist that depend on it.
We already have branches for StringifyWithLegacySemantics
to handle quoted nulls, so we can expand it to handle this.

Fixes #75619

Change-Id: Ic07802539b7cbe0e1f53bd0f7e9bb344a8447203
Reviewed-on: https://go-review.googlesource.com/c/go/+/709615
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index d12495f90b..0b26b8eb91 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -1237,6 +1237,62 @@ var unmarshalTests = []struct {
 		out:      (chan int)(nil),
 		err:      &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[chan int](), Offset: 1},
 	},
+
+	// #75619
+	{
+		CaseName: Name("QuotedInt/GoSyntax"),
+		in:       `{"X": "-0000123"}`,
+		ptr: new(struct {
+			X int64 `json:",string"`
+		}),
+		out: struct {
+			X int64 `json:",string"`
+		}{-123},
+	},
+	{
+		CaseName: Name("QuotedInt/Invalid"),
+		in:       `{"X": "123 "}`,
+		ptr: new(struct {
+			X int64 `json:",string"`
+		}),
+		err: &UnmarshalTypeError{Value: "number 123 ", Type: reflect.TypeFor[int64](), Field: "X", Offset: int64(len(`{"X": "123 "`))},
+	},
+	{
+		CaseName: Name("QuotedUint/GoSyntax"),
+		in:       `{"X": "0000123"}`,
+		ptr: new(struct {
+			X uint64 `json:",string"`
+		}),
+		out: struct {
+			X uint64 `json:",string"`
+		}{123},
+	},
+	{
+		CaseName: Name("QuotedUint/Invalid"),
+		in:       `{"X": "0x123"}`,
+		ptr: new(struct {
+			X uint64 `json:",string"`
+		}),
+		err: &UnmarshalTypeError{Value: "number 0x123", Type: reflect.TypeFor[uint64](), Field: "X", Offset: int64(len(`{"X": "0x123"`))},
+	},
+	{
+		CaseName: Name("QuotedFloat/GoSyntax"),
+		in:       `{"X": "0x1_4p-2"}`,
+		ptr: new(struct {
+			X float64 `json:",string"`
+		}),
+		out: struct {
+			X float64 `json:",string"`
+		}{0x1_4p-2},
+	},
+	{
+		CaseName: Name("QuotedFloat/Invalid"),
+		in:       `{"X": "1.5e1_"}`,
+		ptr: new(struct {
+			X float64 `json:",string"`
+		}),
+		err: &UnmarshalTypeError{Value: "number 1.5e1_", Type: reflect.TypeFor[float64](), Field: "X", Offset: int64(len(`{"X": "1.5e1_"`))},
+	},
 }
 
 func TestMarshal(t *testing.T) {