fix: allow unescaped hyphen in string in some cases

If a string starts with a hyphen (aka: minus sign) but a digit does not immediately follow it, there is no need to escape the hyphen.

Author: aleclarson

spec.md

@@ -98,7 +98,7 @@ For example, these characters are _always_ escaped with a backslash (`\`):
 And these characters are escaped if they're the first character, since they would otherwise imply another data type:
 
 - digits (if not escaped, implies a number)
-- hyphens (if not escaped, implies a negative number)
+- hyphens, but only if followed by a digit (if not escaped, implies a negative number)
 - backslashes (if not escaped, implies an escape sequence)
 
 The following object…

src/charCode.ts

@@ -18,3 +18,7 @@ export const enum CharCode {
   Quote = 39, // '
   Space = 32,
 }
+
+export function isDigit(charCode: number): boolean {
+  return charCode >= CharCode.DigitMin && charCode <= CharCode.DigitMax
+}

src/decode.ts

@@ -1,4 +1,4 @@
-import { CharCode } from './charCode.js'
+import { CharCode, isDigit } from './charCode.js'
 import { CodableObject, CodableValue } from './types.js'
 
 type URLSearchParams = typeof globalThis extends {
@@ -69,11 +69,13 @@ function decodeValue(input: string, cursor = { pos: 0 }): CodableValue {
       break
 
     case CharCode.Minus:
-      mode = ValueMode.NumberOrBigint
+      mode = isDigit(input.charCodeAt(pos + 1))
+        ? ValueMode.NumberOrBigint
+        : ValueMode.String
       break
 
     default:
-      if (charCode >= CharCode.DigitMin && charCode <= CharCode.DigitMax) {
+      if (isDigit(charCode)) {
         mode = ValueMode.NumberOrBigint
       } else {
         endPos = nested ? findEndPos(input, pos) : input.length

src/encode.ts

@@ -1,5 +1,5 @@
 import { isArray } from 'radashi'
-import { CharCode } from './charCode.js'
+import { CharCode, isDigit } from './charCode.js'
 import { CodableObject, CodableValue } from './types.js'
 
 export type EncodeOptions = {
@@ -66,7 +66,7 @@ function encodeValue(value: CodableValue): string {
     }
     // For string values, escape the first character if it's a digit or
     // minus sign, since those are used to detect a number value.
-    return encodeString(value, isNumberLike(value.charCodeAt(0)))
+    return encodeString(value, isNumberLike(value))
   }
   if (typeof value === 'number') {
     if (Number.isNaN(value) || !Number.isFinite(value)) {
@@ -86,6 +86,14 @@ function encodeValue(value: CodableValue): string {
   throw new Error(`Unsupported value type: ${typeof value}`)
 }
 
+function isNumberLike(value: string): boolean {
+  const charCode = value.charCodeAt(0)
+  return (
+    isDigit(charCode) ||
+    (charCode === CharCode.Minus && isDigit(value.charCodeAt(1)))
+  )
+}
+
 function encodeArray(array: readonly CodableValue[]): string {
   let result = ''
   for (let i = 0; i < array.length; i++) {
@@ -106,13 +114,6 @@ function encodeObject(obj: CodableObject): string {
   return `{${encodeProperties(obj, true)}}`
 }
 
-function isNumberLike(charCode: number): boolean {
-  return (
-    (charCode >= CharCode.DigitMin && charCode <= CharCode.DigitMax) ||
-    charCode === CharCode.Minus
-  )
-}
-
 function encodeString(str: string, escape?: boolean): string {
   // Regardless of the escape flag, we always escape backslashes.
   let result = escape || str.charCodeAt(0) === CharCode.Escape ? '\\' : ''

test/cases.ts

@@ -141,6 +141,10 @@ export const cases: Record<string, Case | Case[]> = {
       encoded: 'a=+\\(\\)\\{\\}\\:\\,+',
     },
   ],
+  'string that starts with minus sign but is not a number': {
+    decoded: { sort: '-title' },
+    encoded: 'sort=-title',
+  },
   'non-ASCII characters': [
     {
       decoded: { a: '💩' },