[go] encoding/json: document contrasting v2 behavior in StringifyWithLegacySemantics and UnmarshalArrayFromAnyLength

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Joseph Tsai (Gerrit)

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Jun 9, 2026, 3:23:24 PM (14 hours ago) Jun 9

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encoding/json: document contrasting v2 behavior in StringifyWithLegacySemantics and UnmarshalArrayFromAnyLength

Updates #79733

Change-Id: I97505b8c49152f3880b2c66e87c3b444e28d0b26

Change diff

diff --git a/src/encoding/json/v2_options.go b/src/encoding/json/v2_options.go
index d2414db..d7a95b6 100644
--- a/src/encoding/json/v2_options.go
+++ b/src/encoding/json/v2_options.go
@@ -501,7 +501,12 @@
 // StringifyWithLegacySemantics specifies that the `string` tag option
 // may stringify bools and string values. It only takes effect on fields
 // where the top-level type is a bool, string, numeric kind, or a pointer to
-// such a kind.
+// such a kind. In contrast, the v2 default only allows the `string` tag option
+// on Go types that would have otherwise serialized as a JSON number,
+// and stringifies the JSON number within a a JSON string. In particular,
+// the v2 default does not stringify Go bools and strings.
+// If [ReportErrorsWithLegacySemantics] is false,
+// then incorrect usages of `string` results in a runtime error.
 //
 // When marshaling, such Go values are serialized as their usual JSON
 // representation, but quoted within a JSON string.
@@ -511,6 +516,8 @@
 // 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.
+// In contrast, the v2 default rejects stringified numbers outside of the
+// grammar for a JSON number and also rejects a JSON null quoted in a JSON string.
 //
 // This affects either marshaling or unmarshaling.
 // The v1 default is true.
@@ -526,6 +533,8 @@
 // from input JSON arrays of any length. If the JSON array is too short,
 // then the remaining Go array elements are zeroed. If the JSON array
 // is too long, then the excess JSON array elements are skipped over.
+// In contrast, the v2 default expects that Go arrays be unmarshaled
+// from input JSON arrays of the exact length.
 //
 // This only affects unmarshaling and is ignored when marshaling.
 // The v1 default is true.

Change information

Files:

M src/encoding/json/v2_options.go

Change size: S

Delta: 1 file changed, 10 insertions(+), 1 deletion(-)

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Michael Pratt (Gerrit)

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Jun 9, 2026, 6:19:34 PM (11 hours ago) Jun 9

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File src/encoding/json/v2_options.go

Line 506, Patchset 1 (Latest):// and stringifies the JSON number within a a JSON string. In particular,

Michael Pratt . unresolved

```suggestion
// and stringifies the JSON number within a JSON string. In particular,
```

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