Fix parsing errors on implementation keywords in conditional branches

Author: cirras

delphi-frontend/src/main/antlr3/au/com/integradev/delphi/antlr/Delphi.g

@@ -1503,9 +1503,9 @@ COMMENT                 :  '//' ~('\n'|'\r')*                          {$channel
 
                               if ($text.startsWith(start + "\$")) {
                                 $type = TkCompilerDirective;
-                                if ($text.startsWith(start + "\$endif") || $text.startsWith(start + "\$ifend")) {
+                                if ($text.startsWithIgnoreCase(start + "\$endif") || $text.startsWithIgnoreCase(start + "\$ifend")) {
                                   --directiveNesting;
-                                } else if ($text.startsWith(start + "\$if")) {
+                                } else if ($text.startsWithIgnoreCase(start + "\$if")) {
                                   ++directiveNesting;
                                 }
                               }

delphi-frontend/src/test/java/au/com/integradev/delphi/file/DelphiFileTest.java

@@ -18,8 +18,7 @@
  */
 package au.com.integradev.delphi.file;
 
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.*;
 
 import au.com.integradev.delphi.compiler.Platform;
 import au.com.integradev.delphi.core.Delphi;
@@ -36,6 +35,8 @@
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.sonar.api.batch.fs.InputFile;
 import org.sonar.api.batch.fs.internal.TestInputFileBuilder;
 
@@ -106,4 +107,21 @@ void testByteOrderMarkShouldBeStripped() {
     String firstLine = delphiFile.getSourceCodeFileLines().get(0);
     assertThat(firstLine).doesNotStartWith("\ufeff");
   }
+
+  @ParameterizedTest
+  @ValueSource(strings = {"SkipImplementation.pas", "SkipImplementationWithDirectiveNesting.pas"})
+  void testShouldSkipImplementation(String filename) {
+    File file = DelphiUtils.getResource("/au/com/integradev/delphi/file/" + filename);
+
+    DelphiFileConfig config =
+        DelphiFile.createConfig(
+            StandardCharsets.UTF_8.name(),
+            new DelphiPreprocessorFactory(Platform.WINDOWS),
+            TypeFactoryUtils.defaultFactory(),
+            SearchPath.create(Collections.emptyList()),
+            Collections.emptySet(),
+            true);
+
+    assertThatNoException().isThrownBy(() -> DelphiFile.from(file, config));
+  }
 }

delphi-frontend/src/test/resources/au/com/integradev/delphi/file/SkipImplementation.pas

@@ -0,0 +1,9 @@
+unit SkipImplementation;
+
+interface
+
+implementation
+
+ERROR
+
+end.

delphi-frontend/src/test/resources/au/com/integradev/delphi/file/SkipImplementationWithDirectiveNesting.pas

@@ -0,0 +1,14 @@
+unit SkipImplementationWithDirectiveNesting;
+
+interface
+
+{$If False}
+type
+  TFoo = ERROR class
+  emd;
+implementation
+{$eLsE}
+implementation
+{$endif}
+
+end.