perf(toString): no bounds when duplication is shorter

E.g. render `a{3}` as `aaa` because it's shorter.

Author: gruhn

README.md

@@ -116,17 +116,19 @@ import { RB } from '@gruhn/regex-utils'
 
 const strContainingCommentEnd = RB(/.*-->.*/)
 
-const commentRegex = RB('<!--')
-  .concat(strContainingEndMarker.not())
-  .concat('-->')
+const commentStart = RB('<!--')
+const commentInner = RB(/^.*-->.*$/).not()
+const commentEnd = RB('-->')
+
+const comment = commentStart.concat(commentInner).concat(commentEnd)
 ```
 
 With `.toRegExp()` we can convert back to a native JavaScript regex:
 ```typescript
-commentRegex.toRegExp()
+comment.toRegExp()
 ```
 ```
-/^(<!-{2}(-{2}-*[^->]|-?[^-])*-{2}-*>)$/
+/^<!--(---*[^->]|-?[^-])*---*>$/
 ```
 
 ### Password Regex using Intersections 🔐

benchmark/toStdRegex_output_length-result.txt

@@ -7,11 +7,11 @@ failed instances:
 - regexSyntaxError   : 0
 
 size multipliers:
-- mean   : 323.8333568093031
+- mean   : 321.86932736154387
 - median : 1.1923076923076923
 - max    : 178441.75438596492
 - min    : 0.0021570319240724763
 
 memory:
-- max heap used : 2370.280075073242 MB
-- max rss       : 2722.53515625 MB
+- max heap used : 2491.6993865966797 MB
+- max rss       : 2909.78515625 MB

src/ast.ts

@@ -614,6 +614,10 @@ export function toString(ast: RegExpAST, options: RenderOptions): string {
       const innerStr = maybeWithParens(ast.inner, ast, options)
       if (innerStr === '') 
         return ''
+      else if (typeof ast.bounds === 'number' && ast.bounds <= 3 && innerStr.length === 1)
+        // Just duplicate `innerStr` if that makes rendered expression shorter.
+        // E.g. `aaa` instead of `a{3}`.
+        return innerStr.repeat(ast.bounds)
       else
         return innerStr + repeatBoundsToString(ast.bounds)
     }

test/regex.spec.ts

@@ -264,10 +264,10 @@ describe('derivative', () => {
 
   const derivativeCases = [
     [/^((aa*)?)$/, 'a', /^a*$/],
-    [/^(a{2}(a{3})*)$/, 'a', /^a(a{3})*$/],
+    [/^(a{2}(a{3})*)$/, 'a', /^a(aaa)*$/],
     [/^(a{2}(a*)|(aa*))$/, 'a', /^a?a*$/],
-    [/^(a(a{3})*|(aa*)?)$/, 'a', /^((a{3})*|a*)$/],
-    [/^(a{2}(a{3})*|(aa*)?)$/, 'a', /^(a(a{3})*|a*)$/],
+    [/^(a(a{3})*|(aa*)?)$/, 'a', /^((aaa)*|a*)$/],
+    [/^(a{2}(a{3})*|(aa*)?)$/, 'a', /^(a(aaa)*|a*)$/],
   ] as const
 
   for (const [input, str, expected] of derivativeCases) {