NSRegularExpression: Improved Error and Exception handling to match macOS behaviour

Source/NSRegularExpression.m

@@ -52,6 +52,8 @@
 #import "Foundation/NSCoder.h"
 #import "Foundation/NSUserDefaults.h"
 #import "Foundation/NSNotification.h"
+#import "Foundation/FoundationErrors.h"
+#import "Foundation/NSError.h"
 
 
 /**
@@ -114,6 +116,15 @@ - (id) initWithPattern: (NSString*)aPattern
 	       options: (NSRegularExpressionOptions)opts
 		 error: (NSError**)e
 {
+  // Raise an NSInvalidArgumentException to match macOS behaviour.
+  if (!aPattern) {
+    NSException *exp;
+
+    exp = [NSException exceptionWithName: NSInvalidArgumentException
+          reason: @"nil argument"];
+    [exp raise];
+  }
+
   uint32_t	flags = NSRegularExpressionOptionsToURegexpFlags(opts);
   UText		p = UTEXT_INITIALIZER;
   UParseError	pe = {0};
@@ -131,7 +142,27 @@ - (id) initWithPattern: (NSString*)aPattern
   utext_close(&p);
   if (U_FAILURE(s))
     {
-      // FIXME: Do something sensible with the error parameter.
+      // Match macOS behaviour if the pattern is invalid.
+      // Example:
+      //   Domain=NSCocoaErrorDomain
+      //   Code=2048 "The value “<PATTERN>” is invalid."
+      //   UserInfo={NSInvalidValue=<PATTERN>}
+      if (e) {
+        NSDictionary *userInfo;
+        NSString *description;
+
+        description = [NSString stringWithFormat:
+                       @"The value “%@” is invalid.",
+                       aPattern];
+
+        userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
+                    aPattern, @"NSInvalidValue", description, NSLocalizedDescriptionKey, nil];
+
+        *e = [NSError errorWithDomain: NSCocoaErrorDomain
+                                 code: NSFormattingError
+                             userInfo: userInfo];
+      }
+
       [self release];
       return nil;
     }

Tests/base/NSRegularExpression/basic.m

@@ -9,6 +9,8 @@
 #import <Foundation/NSRunLoop.h>
 #import <Foundation/NSThread.h>
 #import <Foundation/NSValue.h>
+#import <Foundation/NSError.h>
+#import <Foundation/FoundationErrors.h>
 
 @interface DegeneratePatternTest : NSObject
 {
@@ -169,6 +171,38 @@ int main()
        beforeDate: [NSDate dateWithTimeIntervalSinceNow: 0.01]];
     }
   PASS(NO == [thread isExecuting], "Faulty regular expression terminated");
+
+  /* Testing the error handling when an invalid pattern is passed
+   * The error should look like this:
+   *
+   * Error Domain=NSCocoaErrorDomain Code=2048 "The value “(abc” is
+   * invalid." UserInfo={NSInvalidValue=(abc}
+   */
+
+  NSError *error = nil;
+  NSRegularExpression *testObj3 =
+    [[NSRegularExpression alloc] initWithPattern: @"(abc"
+           options: 0
+             error: &error];
+  PASS(testObj3 == nil, "Invalid pattern: returns nil");
+  PASS(error != nil, "Invalid pattern: error is set");
+  PASS_EQUAL([error domain], NSCocoaErrorDomain,
+             "Invalid pattern: error domain is NSCocoaErrorDomain");
+  PASS_EQUAL([error code], NSFormattingError, 
+             "Invalid pattern: error code is NSFormattingError");
+  PASS_EQUAL([[error userInfo] objectForKey: @"NSInvalidValue"],
+             @"(abc", "Invalid pattern: error message is correct");
+  PASS_EQUAL([[error userInfo] objectForKey: NSLocalizedDescriptionKey],
+             @"The value “(abc” is invalid.",
+             "Invalid pattern: localized description is correct");
+
+  /* Testing exception handling when nil is passed as pattern */
+  PASS_EXCEPTION([NSRegularExpression regularExpressionWithPattern: nil
+                                                           options: 0
+                                                             error: NULL],
+                 NSInvalidArgumentException,
+                 "nil pattern: throws NSInvalidArgumentException");
+
 #endif
 
   END_SET("NSRegularExpression")