#2142: Strip leading underscore when sanitizing identifier name

processor/src/main/java/org/mapstruct/ap/internal/model/ForgedMethod.java

@@ -125,8 +125,7 @@ public class ForgedMethod implements Method {
                          boolean forgedNameBased) {
 
         // establish name
-        String sourceParamName = Strings.decapitalize( sourceType.getName() );
-        String sourceParamSafeName = Strings.getSafeVariableName( sourceParamName );
+        String sourceParamSafeName = Strings.getSafeVariableName( sourceType.getName() );
 
         // establish parameters
         this.parameters = new ArrayList<>( 1 + additionalParameters.size() );

processor/src/main/java/org/mapstruct/ap/internal/util/Strings.java

@@ -73,6 +73,8 @@ public class Strings {
         "while"
     );
 
+    private static final char UNDERSCORE = '_';
+
     private Strings() {
     }
 
@@ -166,7 +168,22 @@ public class Strings {
      * @return the identifier without any characters that are not allowed as part of a Java identifier.
      */
     public static String sanitizeIdentifierName(String identifier) {
-        return identifier.replace( "[]", "Array" );
+        if ( identifier != null && identifier.length() > 0 ) {
+
+            int firstNonUnderScoreIndex = 0;
+            while ( firstNonUnderScoreIndex < identifier.length() &&
+                identifier.charAt( firstNonUnderScoreIndex ) == UNDERSCORE ) {
+                firstNonUnderScoreIndex++;
+            }
+
+            if ( firstNonUnderScoreIndex < identifier.length()) {
+                // If it is not consisted of only underscores
+                return identifier.substring( firstNonUnderScoreIndex ).replace( "[]", "Array" );
+            }
+
+            return identifier.replace( "[]", "Array" );
+        }
+        return identifier;
     }
 
     /**

processor/src/test/java/org/mapstruct/ap/internal/util/StringsTest.java

@@ -83,6 +83,8 @@ public class StringsTest {
         assertThat( Strings.getSafeVariableName( "Case" ) ).isEqualTo( "case1" );
         assertThat( Strings.getSafeVariableName( "Synchronized" ) ).isEqualTo( "synchronized1" );
         assertThat( Strings.getSafeVariableName( "prop", "prop", "prop_" ) ).isEqualTo( "prop1" );
+        assertThat( Strings.getSafeVariableName( "_Test" ) ).isEqualTo( "test" );
+        assertThat( Strings.getSafeVariableName( "__Test" ) ).isEqualTo( "test" );
     }
 
     @Test
@@ -98,12 +100,20 @@ public class StringsTest {
         assertThat( Strings.getSafeVariableName( "prop", Arrays.asList( "prop", "prop1" ) ) ).isEqualTo( "prop2" );
         assertThat( Strings.getSafeVariableName( "prop.font", Arrays.asList( "propFont", "propFont_" ) ) )
             .isEqualTo( "propFont1" );
+        assertThat( Strings.getSafeVariableName( "_Test", new ArrayList<>() ) ).isEqualTo( "test" );
+        assertThat( Strings.getSafeVariableName( "__Test", Arrays.asList( "test" ) ) ).isEqualTo( "test1" );
+        assertThat( Strings.getSafeVariableName( "___", new ArrayList<>() ) ).isEqualTo( "___" );
     }
 
     @Test
     public void testSanitizeIdentifierName() {
         assertThat( Strings.sanitizeIdentifierName( "test" ) ).isEqualTo( "test" );
         assertThat( Strings.sanitizeIdentifierName( "int[]" ) ).isEqualTo( "intArray" );
+        assertThat( Strings.sanitizeIdentifierName( "_Test" ) ).isEqualTo( "Test" );
+        assertThat( Strings.sanitizeIdentifierName( "_int[]" ) ).isEqualTo( "intArray" );
+        assertThat( Strings.sanitizeIdentifierName( "__int[]" ) ).isEqualTo( "intArray" );
+        assertThat( Strings.sanitizeIdentifierName( "test_" ) ).isEqualTo( "test_" );
+        assertThat( Strings.sanitizeIdentifierName( "___" ) ).isEqualTo( "___" );
     }
 
     @Test

processor/src/test/java/org/mapstruct/ap/test/bugs/_2142/Issue2142Mapper.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._2142;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface Issue2142Mapper {
+
+    Issue2142Mapper INSTANCE = Mappers.getMapper( Issue2142Mapper.class );
+
+    _Target map(Source source);
+
+    // CHECKSTYLE:OFF
+    class _Target {
+    // CHECKSTYLE:ON
+        private final String value;
+
+        public _Target(String value) {
+            this.value = value;
+        }
+
+        public String getValue() {
+            return value;
+        }
+    }
+
+    class Source {
+        private final String value;
+
+        public Source(String value) {
+            this.value = value;
+        }
+
+        public String getValue() {
+            return value;
+        }
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2142/Issue2142Test.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._2142;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+import org.mapstruct.ap.testutil.runner.GeneratedSource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@IssueKey("2142")
+@WithClasses(Issue2142Mapper.class)
+@RunWith(AnnotationProcessorTestRunner.class)
+public class Issue2142Test {
+
+    @Rule
+    public final GeneratedSource generatedSource = new GeneratedSource()
+        .addComparisonToFixtureFor( Issue2142Mapper.class );
+
+    @Test
+    public void underscorePrefixShouldBeStrippedFromGeneratedLocalVariables() {
+        Issue2142Mapper._Target target = Issue2142Mapper.INSTANCE.map( new Issue2142Mapper.Source( "value1" ) );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getValue() ).isEqualTo( "value1" );
+    }
+}

processor/src/test/resources/fixtures/org/mapstruct/ap/test/bugs/_2142/Issue2142MapperImpl.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._2142;
+
+import javax.annotation.Generated;
+
+@Generated(
+    value = "org.mapstruct.ap.MappingProcessor",
+    date = "2019-02-10T09:58:11+0100",
+    comments = "version: , compiler: javac, environment: Java 1.8.0_181 (Oracle Corporation)"
+)
+public class Issue2142MapperImpl implements Issue2142Mapper {
+
+    @Override
+    public _Target map(Source source) {
+        if ( source == null ) {
+            return null;
+        }
+
+        String value = null;
+
+        value = source.getValue();
+
+        _Target target = new _Target( value );
+
+        return target;
+    }
+}