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>

4 files changed, 157 insertions, 10 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) {
diff --git a/src/encoding/json/v2/arshal_default.go b/src/encoding/json/v2/arshal_default.go
index c2307fa31d..078d345e14 100644
--- a/src/encoding/json/v2/arshal_default.go
+++ b/src/encoding/json/v2/arshal_default.go
@@ -474,10 +474,21 @@ func makeIntArshaler(t reflect.Type) *arshaler {
 				break
 			}
 			val = jsonwire.UnquoteMayCopy(val, flags.IsVerbatim())
-			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) && string(val) == "null" {
-				if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
-					va.SetInt(0)
+			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) {
+				// For historical reasons, v1 parsed a quoted number
+				// according to the Go syntax and permitted a quoted null.
+				// See https://go.dev/issue/75619
+				n, err := strconv.ParseInt(string(val), 10, bits)
+				if err != nil {
+					if string(val) == "null" {
+						if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
+							va.SetInt(0)
+						}
+						return nil
+					}
+					return newUnmarshalErrorAfterWithValue(dec, t, errors.Unwrap(err))
 				}
+				va.SetInt(n)
 				return nil
 			}
 			fallthrough
@@ -561,10 +572,21 @@ func makeUintArshaler(t reflect.Type) *arshaler {
 				break
 			}
 			val = jsonwire.UnquoteMayCopy(val, flags.IsVerbatim())
-			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) && string(val) == "null" {
-				if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
-					va.SetUint(0)
+			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) {
+				// For historical reasons, v1 parsed a quoted number
+				// according to the Go syntax and permitted a quoted null.
+				// See https://go.dev/issue/75619
+				n, err := strconv.ParseUint(string(val), 10, bits)
+				if err != nil {
+					if string(val) == "null" {
+						if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
+							va.SetUint(0)
+						}
+						return nil
+					}
+					return newUnmarshalErrorAfterWithValue(dec, t, errors.Unwrap(err))
 				}
+				va.SetUint(n)
 				return nil
 			}
 			fallthrough
@@ -671,10 +693,21 @@ func makeFloatArshaler(t reflect.Type) *arshaler {
 			if !stringify {
 				break
 			}
-			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) && string(val) == "null" {
-				if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
-					va.SetFloat(0)
+			if uo.Flags.Get(jsonflags.StringifyWithLegacySemantics) {
+				// For historical reasons, v1 parsed a quoted number
+				// according to the Go syntax and permitted a quoted null.
+				// See https://go.dev/issue/75619
+				n, err := strconv.ParseFloat(string(val), bits)
+				if err != nil {
+					if string(val) == "null" {
+						if !uo.Flags.Get(jsonflags.MergeWithLegacySemantics) {
+							va.SetFloat(0)
+						}
+						return nil
+					}
+					return newUnmarshalErrorAfterWithValue(dec, t, errors.Unwrap(err))
 				}
+				va.SetFloat(n)
 				return nil
 			}
 			if n, err := jsonwire.ConsumeNumber(val); n != len(val) || err != nil {
diff --git a/src/encoding/json/v2_decode_test.go b/src/encoding/json/v2_decode_test.go
index f9b0a60f47..28c57ec8bf 100644
--- a/src/encoding/json/v2_decode_test.go
+++ b/src/encoding/json/v2_decode_test.go
@@ -1243,6 +1243,62 @@ var unmarshalTests = []struct {
 		out:      (chan int)(nil),
 		err:      &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[chan int]()},
 	},
+
+	// #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": `))},
+	},
+	{
+		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": `))},
+	},
+	{
+		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": `))},
+	},
 }
 
 func TestMarshal(t *testing.T) {
diff --git a/src/encoding/json/v2_options.go b/src/encoding/json/v2_options.go
index 4dea88ad7e..819fe59f41 100644
--- a/src/encoding/json/v2_options.go
+++ b/src/encoding/json/v2_options.go
@@ -506,7 +506,9 @@ func ReportErrorsWithLegacySemantics(v bool) Options {
 // When marshaling, such Go values are serialized as their usual
 // JSON representation, but quoted within a JSON string.
 // When unmarshaling, such Go values must be deserialized from
-// a JSON string containing their usual JSON representation.
+// a JSON string containing their usual JSON representation or
+// Go number representation for that numeric kind.
+// Note that the Go number grammar is a superset of the JSON number grammar.
 // A JSON null quoted in a JSON string is a valid substitute for JSON null
 // while unmarshaling into a Go value that `string` takes effect on.
 //