fix(parser): ] only needs escape after [

Author: gruhn

src/code-point-range.ts

@@ -112,11 +112,11 @@ export function difference(rangeA: CodePointRange, rangeB: CodePointRange): [] |
 /**
  * Returns true iff the given char must always be escaped to occur literally
  * in a regular expression. Some special chars like `$` don't need to be 
- * escaped when inside brackets (e.g. `/[$]/`). But `\` and `]` must 
- * even be escaped when inside brackets. 
+ * escaped when inside brackets (e.g. `/[$]/`). But `\` must even be
+ * escaped when inside brackets. And `]` must only be escaped inside brackets.
  */
-export function mustAlwaysBeEscaped(char: string) {
-  return '\\\]/'.includes(char)
+export function mustBeEscapedInsideBrackets(char: string) {
+  return char === '\\' || char === ']'
 }
 
 /**
@@ -125,18 +125,14 @@ export function mustAlwaysBeEscaped(char: string) {
  * for special chars like `$`. Outside brackets we have to write `\$`. 
  * Inside brackets `[$]` is allowed.
  */
-export function mustBeEscapedOrInBrackets(char: string) {
-  return '.^$*+?()[|/'.includes(char)
-}
-
-export function neverMustBeEscaped(char: string) {
-  return !mustAlwaysBeEscaped(char) && !mustBeEscapedOrInBrackets(char)
+export function mustBeEscapedOutsideBrackets(char: string) {
+  return '.^$*+?()[|/\\'.includes(char)
 }
 
 function codePointToString(codePoint: number): string {
   const char = String.fromCharCode(codePoint)
 
-  if (mustAlwaysBeEscaped(char) || mustBeEscapedOrInBrackets(char)) 
+  if (mustBeEscapedInsideBrackets(char) || mustBeEscapedOutsideBrackets(char)) 
     // e.g. \$ \+ \. 
     return '\\' + char
   else if (codePoint > 126)

src/regex-parser.ts

@@ -37,11 +37,12 @@ const wildcard = P.string('.').map(
   () => RE.literal(CharSet.wildcard({ dotAll: false }))
 )
 
-const unescapedChar = P.satisfy(Range.neverMustBeEscaped)
-
 const alphaNumChar = P.satisfy(char => /^[a-zA-Z0-9]$/.test(char))
 
-const unescapedCharInsideBrackets = P.satisfy(Range.mustBeEscapedOrInBrackets)
+const unescapedCharInsideBrackets = P.satisfy(char => !Range.mustBeEscapedInsideBrackets(char))
+  .map(CharSet.singleton)
+
+const unescapedCharOutsideBrackets = P.satisfy(char => !Range.mustBeEscapedOutsideBrackets(char))
   .map(CharSet.singleton)
 
 export class UnsupportedSyntaxError extends Error {}
@@ -96,15 +97,14 @@ const alphaNumRange: P.Parser<CharSet.CharSet> = alphaNumChar.andThen(start =>
 
 const charSet = P.choice([
   P.between(
-    // QUESTION: can brackets be nested?
+    // square brackets cant't be nested
     P.string('['),
     P.string(']'),
     P.optional(P.string('^')).andThen(negated =>
       P.many(P.choice([
         escapeSequence, // e.g. "\$", "\]"
         alphaNumRange, // e.g. "a-z", "0-9" (will also match just "a", "3")
         unescapedCharInsideBrackets, // e.g. "$", "."
-        unescapedChar.map(CharSet.singleton), // e.g. "#", "%"
       ])).map(
         sets => {
           if (negated === undefined)
@@ -115,7 +115,7 @@ const charSet = P.choice([
       )
     )
   ),
-  unescapedChar.map(CharSet.singleton),
+  unescapedCharOutsideBrackets,
 ])
 
 const group = P.between(