[Python] Some regex patterns can generate invalid code. #6675 (#10920)

* fix issue 6675 & add javadoc

* fix formatting issue

* update JUnit test for 6675

* build & update samples for PR

* clean package and regenerating samples

* add progress for fix to issue 10957

* Revert "add progress for fix to issue 10957"

This reverts commit 8240c7ccb17141f7551ab34eda864ab4e068ebd8.

* fix version issues

* fix more versioning issues

* fix discrepancies with backslashes

* update samples

Co-authored-by: William Cheng <wing328hk@gmail.com>

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PythonLegacyClientCodegen.java

@@ -311,6 +311,13 @@ public class PythonLegacyClientCodegen extends AbstractPythonCodegen implements
      * The OpenAPI pattern spec follows the Perl convention and style of modifiers. Python
      * does not support this in as natural a way so it needs to convert it. See
      * https://docs.python.org/2/howto/regex.html#compilation-flags for details.
+	 *
+	 * @param pattern (the String pattern to convert from python to Perl convention)
+	 * @param vendorExtensions (list of custom x-* properties for extra functionality-see https://swagger.io/docs/specification/openapi-extensions/)
+	 * @return void
+	 * @throws IllegalArgumentException if pattern does not follow the Perl /pattern/modifiers convention
+	 *
+	 * Includes fix for issue #6675
      */
     public void postProcessPattern(String pattern, Map<String, Object> vendorExtensions) {
         if (pattern != null) {
@@ -321,6 +328,13 @@ public class PythonLegacyClientCodegen extends AbstractPythonCodegen implements
                 throw new IllegalArgumentException("Pattern must follow the Perl "
                         + "/pattern/modifiers convention. " + pattern + " is not valid.");
             }
+			
+	    //check for instances of extra backslash that could cause compile issues and remove
+	    int firstBackslash = pattern.indexOf("\\");
+            int bracket = pattern.indexOf("[");
+            if (firstBackslash == 0 || firstBackslash == 1 || firstBackslash == bracket+1) {
+                pattern = pattern.substring(0,firstBackslash)+pattern.substring(firstBackslash+1);
+            }
 
             String regex = pattern.substring(1, i).replace("'", "\\'");
             List<String> modifiers = new ArrayList<String>();

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonLegacyClientCodegenTest.java

@@ -91,6 +91,9 @@ public class PythonLegacyClientCodegenTest {
         Assert.assertEquals(op.allParams.get(4).pattern, "/^pattern\\/\\d{3}$/");
         // pattern_with_modifiers '/^pattern\d{3}$/i
         Assert.assertEquals(op.allParams.get(5).pattern, "/^pattern\\d{3}$/i");
+        // pattern_with_backslash_after_bracket '/^[\pattern\d{3}$/i'
+        // added to test fix for issue #6675
+        Assert.assertEquals(op.allParams.get(6).pattern, "/^[\\pattern\\d{3}$/i");
     }
 
 

modules/openapi-generator/src/test/resources/3_0/issue_1517.yaml

@@ -45,6 +45,11 @@ paths:
           schema:
             type: string
             pattern: '/^pattern\d{3}$/i'
+        - name: pattern_with_backslash_after_bracket
+          in: header
+          schema:
+            type: string
+            pattern: '/^[\pattern\d{3}$/i'
 
       responses:
         '200':