#2840, #2913, #2921: MethodMatcher should not match widening methods

In the MethodMatcher we need to do a special check when the target type is primitive.
The reason for that is that a Long is assignable to a primitive double.
However, doing that means that information can be lost and thus we should not pick such methods.
When the target type is primitive, then a method will be matched if and only if boxed equivalent of the target type is assignable to the boxed equivalent of the candidate return type

processor/src/main/java/org/mapstruct/ap/internal/model/source/MethodMatcher.java

@@ -82,6 +82,17 @@ public class MethodMatcher {
         // (the relation target / target type, target type being a class)
 
         if ( !analyser.candidateReturnType.isVoid() ) {
+            if ( targetType.isPrimitive() ) {
+                // If the target type is primitive
+                // then we are going to check if its boxed equivalent
+                // is assignable to the candidate return type
+                // This is done because primitives can be assigned from their own narrower counterparts
+                // directly without any casting.
+                // e.g. a Long is assignable to a primitive double
+                // However, in order not to lose information we are not going to allow this
+                return targetType.getBoxedEquivalent()
+                    .isAssignableTo( analyser.candidateReturnType.getBoxedEquivalent() );
+            }
             if ( !( analyser.candidateReturnType.isAssignableTo( targetType ) ) ) {
                 return false;
             }

processor/src/test/java/org/mapstruct/ap/test/bugs/_2840/Issue2840Mapper.java

@@ -0,0 +1,51 @@
+/*
+ * 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._2840;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface Issue2840Mapper {
+
+    Issue2840Mapper INSTANCE =
+        Mappers.getMapper( Issue2840Mapper.class );
+
+    Issue2840Mapper.Target map(Short shortValue, Integer intValue);
+
+    default int toInt(Number number) {
+        return number.intValue() + 5;
+    }
+
+    default short toShort(Number number) {
+        return (short) (number.shortValue() + 10);
+    }
+
+    class Target {
+
+        private int intValue;
+        private short shortValue;
+
+        public int getIntValue() {
+            return intValue;
+        }
+
+        public void setIntValue(int intValue) {
+            this.intValue = intValue;
+        }
+
+        public short getShortValue() {
+            return shortValue;
+        }
+
+        public void setShortValue(short shortValue) {
+            this.shortValue = shortValue;
+        }
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2840/Issue2840Test.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._2840;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2840")
+@WithClasses({
+    Issue2840Mapper.class,
+})
+class Issue2840Test {
+
+    @ProcessorTest
+    void shouldUseMethodWithMostSpecificReturnType() {
+        Issue2840Mapper.Target target = Issue2840Mapper.INSTANCE.map( (short) 10, 50 );
+
+        assertThat( target.getShortValue() ).isEqualTo( (short) 20 );
+        assertThat( target.getIntValue() ).isEqualTo( 55 );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2913/Issue2913Mapper.java

@@ -0,0 +1,85 @@
+/*
+ * 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._2913;
+
+import java.math.BigDecimal;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface Issue2913Mapper {
+
+    Issue2913Mapper INSTANCE = Mappers.getMapper( Issue2913Mapper.class );
+
+    @Mapping(target = "doublePrimitiveValue", source = "rounding")
+    @Mapping(target = "doubleValue", source = "rounding")
+    @Mapping(target = "longPrimitiveValue", source = "rounding")
+    @Mapping(target = "longValue", source = "rounding")
+    Target map(Source source);
+
+    default Long mapAmount(BigDecimal amount) {
+        return amount != null ? amount.movePointRight( 2 ).longValue() : null;
+    }
+
+    class Target {
+
+        private double doublePrimitiveValue;
+        private Double doubleValue;
+        private long longPrimitiveValue;
+        private Long longValue;
+
+        public double getDoublePrimitiveValue() {
+            return doublePrimitiveValue;
+        }
+
+        public void setDoublePrimitiveValue(double doublePrimitiveValue) {
+            this.doublePrimitiveValue = doublePrimitiveValue;
+        }
+
+        public Double getDoubleValue() {
+            return doubleValue;
+        }
+
+        public void setDoubleValue(Double doubleValue) {
+            this.doubleValue = doubleValue;
+        }
+
+        public long getLongPrimitiveValue() {
+            return longPrimitiveValue;
+        }
+
+        public void setLongPrimitiveValue(long longPrimitiveValue) {
+            this.longPrimitiveValue = longPrimitiveValue;
+        }
+
+        public Long getLongValue() {
+            return longValue;
+        }
+
+        public void setLongValue(Long longValue) {
+            this.longValue = longValue;
+        }
+    }
+
+    class Source {
+
+        private final BigDecimal rounding;
+
+        public Source(BigDecimal rounding) {
+            this.rounding = rounding;
+        }
+
+        public BigDecimal getRounding() {
+            return rounding;
+        }
+    }
+
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2913/Issue2913Test.java

@@ -0,0 +1,35 @@
+/*
+ * 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._2913;
+
+import java.math.BigDecimal;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2913")
+@WithClasses({
+    Issue2913Mapper.class,
+})
+class Issue2913Test {
+
+    @ProcessorTest
+    void shouldNotWidenWithUserDefinedMethods() {
+        Issue2913Mapper.Source source = new Issue2913Mapper.Source( BigDecimal.valueOf( 10.543 ) );
+        Issue2913Mapper.Target target = Issue2913Mapper.INSTANCE.map( source );
+
+        assertThat( target.getDoubleValue() ).isEqualTo( 10.543 );
+        assertThat( target.getDoublePrimitiveValue() ).isEqualTo( 10.543 );
+        assertThat( target.getLongValue() ).isEqualTo( 1054 );
+        assertThat( target.getLongPrimitiveValue() ).isEqualTo( 1054 );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2921/Issue2921Mapper.java

@@ -0,0 +1,49 @@
+/*
+ * 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._2921;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface Issue2921Mapper {
+
+    Issue2921Mapper INSTANCE = Mappers.getMapper( Issue2921Mapper.class );
+
+    Target map(Source source);
+
+    default Short toShort(Integer value) {
+        throw new UnsupportedOperationException( "toShort method should not be used" );
+    }
+
+    class Source {
+        private final Integer value;
+
+        public Source(Integer value) {
+            this.value = value;
+        }
+
+        public Integer getValue() {
+            return value;
+        }
+    }
+
+    class Target {
+        private final int value;
+
+        public Target(int value) {
+            this.value = value;
+        }
+
+        public int getValue() {
+            return value;
+        }
+    }
+
+}

processor/src/test/java/org/mapstruct/ap/test/bugs/_2921/Issue2921Test.java

@@ -0,0 +1,28 @@
+/*
+ * 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._2921;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.ProcessorTest;
+import org.mapstruct.ap.testutil.WithClasses;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2921")
+@WithClasses({
+    Issue2921Mapper.class,
+})
+class Issue2921Test {
+
+    @ProcessorTest
+    void shouldNotUseIntegerToShortForMappingIntegerToInt() {
+        Issue2921Mapper.Target target = Issue2921Mapper.INSTANCE.map( new Issue2921Mapper.Source( 10 ) );
+        assertThat( target.getValue() ).isEqualTo( 10 );
+    }
+}