[repo-assist] perf: cache compiled Regex per pattern in JsonSchema.validate

RELEASE_NOTES.md

@@ -1,5 +1,9 @@
 # Release Notes
 
+## 8.2.1 - Sep 28 2026
+
+- Perf: `JsonSchema.validate` now caches compiled `Regex` instances per `pattern`, instead of recompiling a new `Regex` for every string value validated against a schema `pattern` constraint. No behavior change.
+
 ## 8.2.0 - Jul 06 2026
 
 - Fix: HTML hexadecimal character references (`A`) are now decoded correctly; previously digit-only hex refs were parsed as decimal and refs containing `a`–`f` were left as literal text.

src/FSharp.Data.Json.Core/JsonSchema.fs

@@ -366,6 +366,14 @@ module JsonSchema =
 
         resolve schema
 
+    // Cache compiled regexes by pattern so repeated validation of many values against
+    // the same schema pattern (e.g. array/object properties) doesn't recompile the regex each time.
+    let private patternRegexCache =
+        System.Collections.Concurrent.ConcurrentDictionary<string, System.Text.RegularExpressions.Regex>()
+
+    let private getPatternRegex (pattern: string) =
+        patternRegexCache.GetOrAdd(pattern, (fun p -> System.Text.RegularExpressions.Regex(p)))
+
     /// Validate a JSON value against a schema
     let rec validate (schema: JsonSchemaDefinition) (value: JsonValue) : ValidationResult =
         // Check nulls first
@@ -388,7 +396,7 @@ module JsonSchema =
                         // Validate pattern
                         match schema.Pattern with
                         | Some pattern ->
-                            let regex = System.Text.RegularExpressions.Regex(pattern)
+                            let regex = getPatternRegex pattern
 
                             if regex.IsMatch(str) then
                                 Valid