std.json: Parse -0 as a float instead of an integer (#17729)

This is consistent with `JSON.parse("-0")` in JavaScript, RFC 8259
doesn't specifically mention what to do in this case.
If a negative zero is encoded the intention is likely to preserve the
sign.

lib/std/json/dynamic_test.zig

@@ -339,6 +339,17 @@ test "many object keys" {
     try testing.expectEqualStrings("v5", parsed.value.object.get("k5").?.string);
 }
 
+test "negative zero" {
+    const doc = "-0";
+    var fbs = std.io.fixedBufferStream(doc);
+    var reader = smallBufferJsonReader(testing.allocator, fbs.reader());
+    defer reader.deinit();
+    var parsed = try parseFromTokenSource(Value, testing.allocator, &reader, .{});
+    defer parsed.deinit();
+
+    try testing.expect(parsed.value.float == 0 and std.math.signbit(parsed.value.float));
+}
+
 fn smallBufferJsonReader(allocator: Allocator, io_reader: anytype) JsonReader(16, @TypeOf(io_reader)) {
     return JsonReader(16, @TypeOf(io_reader)).init(allocator, io_reader);
 }

lib/std/json/scanner.zig

@@ -1700,11 +1700,12 @@ fn appendSlice(list: *std.ArrayList(u8), buf: []const u8, max_value_len: usize)
 }
 
 /// For the slice you get from a `Token.number` or `Token.allocated_number`,
-/// this function returns true if the number doesn't contain any fraction or exponent components.
+/// this function returns true if the number doesn't contain any fraction or exponent components, and is not `-0`.
 /// Note, the numeric value encoded by the value may still be an integer, such as `1.0`.
 /// This function is meant to give a hint about whether integer parsing or float parsing should be used on the value.
 /// This function will not give meaningful results on non-numeric input.
 pub fn isNumberFormattedLikeAnInteger(value: []const u8) bool {
+    if (std.mem.eql(u8, value, "-0")) return false;
     return std.mem.indexOfAny(u8, value, ".eE") == null;
 }
 

lib/std/json/scanner_test.zig

@@ -7,6 +7,7 @@ const TokenType = @import("./scanner.zig").TokenType;
 const Diagnostics = @import("./scanner.zig").Diagnostics;
 const Error = @import("./scanner.zig").Error;
 const validate = @import("./scanner.zig").validate;
+const isNumberFormattedLikeAnInteger = @import("./scanner.zig").isNumberFormattedLikeAnInteger;
 
 const example_document_str =
     \\{
@@ -465,3 +466,15 @@ test "enableDiagnostics" {
         try testDiagnostics(error.SyntaxError, 1, s.len, s.len - 1, s);
     }
 }
+
+test isNumberFormattedLikeAnInteger {
+    try std.testing.expect(isNumberFormattedLikeAnInteger("0"));
+    try std.testing.expect(isNumberFormattedLikeAnInteger("1"));
+    try std.testing.expect(isNumberFormattedLikeAnInteger("123"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("-0"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("0.0"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("1.0"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("1.23"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("1e10"));
+    try std.testing.expect(!isNumberFormattedLikeAnInteger("1E10"));
+}