lib/json: fix go1.17 build by avoiding reflect.Value.UnsafePointer (#474

)

Fixes #473

lib/json/json.go

@@ -26,29 +26,30 @@ import (
 
 // Module json is a Starlark module of JSON-related functions.
 //
-//   json = module(
-//      encode,
-//      decode,
-//      indent,
-//   )
+//	json = module(
+//	   encode,
+//	   decode,
+//	   indent,
+//	)
 //
 // def encode(x):
 //
 // The encode function accepts one required positional argument,
 // which it converts to JSON by cases:
-// - A Starlark value that implements Go's standard json.Marshal
-//   interface defines its own JSON encoding.
-// - None, True, and False are converted to null, true, and false, respectively.
-// - Starlark int values, no matter how large, are encoded as decimal integers.
-//   Some decoders may not be able to decode very large integers.
-// - Starlark float values are encoded using decimal point notation,
-//   even if the value is an integer.
-//   It is an error to encode a non-finite floating-point value.
-// - Starlark strings are encoded as JSON strings, using UTF-16 escapes.
-// - a Starlark IterableMapping (e.g. dict) is encoded as a JSON object.
-//   It is an error if any key is not a string.
-// - any other Starlark Iterable (e.g. list, tuple) is encoded as a JSON array.
-// - a Starlark HasAttrs (e.g. struct) is encoded as a JSON object.
+//   - A Starlark value that implements Go's standard json.Marshal
+//     interface defines its own JSON encoding.
+//   - None, True, and False are converted to null, true, and false, respectively.
+//   - Starlark int values, no matter how large, are encoded as decimal integers.
+//     Some decoders may not be able to decode very large integers.
+//   - Starlark float values are encoded using decimal point notation,
+//     even if the value is an integer.
+//     It is an error to encode a non-finite floating-point value.
+//   - Starlark strings are encoded as JSON strings, using UTF-16 escapes.
+//   - a Starlark IterableMapping (e.g. dict) is encoded as a JSON object.
+//     It is an error if any key is not a string.
+//   - any other Starlark Iterable (e.g. list, tuple) is encoded as a JSON array.
+//   - a Starlark HasAttrs (e.g. struct) is encoded as a JSON object.
+//
 // It an application-defined type matches more than one the cases describe above,
 // (e.g. it implements both Iterable and HasFields), the first case takes precedence.
 // Encoding any other value yields an error.
@@ -57,10 +58,11 @@ import (
 //
 // The decode function has one required positional parameter, a JSON string.
 // It returns the Starlark value that the string denotes.
-// - Numbers are parsed as int or float, depending on whether they
-//   contain a decimal point.
-// - JSON objects are parsed as new unfrozen Starlark dicts.
-// - JSON arrays are parsed as new unfrozen Starlark lists.
+//   - Numbers are parsed as int or float, depending on whether they
+//     contain a decimal point.
+//   - JSON objects are parsed as new unfrozen Starlark dicts.
+//   - JSON arrays are parsed as new unfrozen Starlark lists.
+//
 // If x is not a valid JSON string, the behavior depends on the "default"
 // parameter: if present, Decode returns its value; otherwise, Decode fails.
 //
@@ -71,7 +73,6 @@ import (
 // It accepts one required positional parameter, the JSON string,
 // and two optional keyword-only string parameters, prefix and indent,
 // that specify a prefix of each new line, and the unit of indentation.
-//
 var Module = &starlarkstruct.Module{
 	Name: "json",
 	Members: starlark.StringDict{
@@ -235,7 +236,8 @@ func pointer(i interface{}) unsafe.Pointer {
 	v := reflect.ValueOf(i)
 	switch v.Kind() {
 	case reflect.Ptr, reflect.Chan, reflect.Map, reflect.UnsafePointer, reflect.Slice:
-		return v.UnsafePointer()
+		// TODO(adonovan): use v.Pointer() when we drop go1.17.
+		return unsafe.Pointer(v.Pointer())
 	default:
 		return nil
 	}