Make Comparators.max/min return the type of the comparands, even …

…if the `Comparator` accepts a more general type.

RELNOTES=n/a
PiperOrigin-RevId: 623747164

android/guava-tests/test/com/google/common/collect/ComparatorsTest.java

@@ -97,6 +97,29 @@ public void testMinMaxComparator() {
     assertThat(Comparators.max(2, 1, reverse)).isEqualTo(1);
   }
 
+  /**
+   * Fails compilation if the signature of min and max is changed to take {@code Comparator<T>}
+   * instead of {@code Comparator<? super T>}.
+   */
+  public void testMinMaxWithSupertypeComparator() {
+    Comparator<Number> numberComparator =
+        // Can't use Comparator.comparing(Number::intValue) due to Java 7 compatibility.
+        new Comparator<Number>() {
+          @Override
+          public int compare(Number a, Number b) {
+            return a.intValue() - b.intValue();
+          }
+        };
+    Integer comparand1 = 1;
+    Integer comparand2 = 2;
+
+    Integer min = Comparators.min(comparand1, comparand2, numberComparator);
+    Integer max = Comparators.max(comparand1, comparand2, numberComparator);
+
+    assertThat(min).isEqualTo(1);
+    assertThat(max).isEqualTo(2);
+  }
+
   public void testMinMaxComparator_equalInstances() {
     Comparator<Foo> natural = Ordering.natural();
     Comparator<Foo> reverse = Collections.reverseOrder(natural);

android/guava/src/com/google/common/collect/Comparators.java

@@ -202,7 +202,7 @@ public static <T extends Comparable<? super T>> T min(T a, T b) {
    */
   @ParametricNullness
   public static <T extends @Nullable Object> T min(
-      @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) {
+      @ParametricNullness T a, @ParametricNullness T b, Comparator<? super T> comparator) {
     return (comparator.compare(a, b) <= 0) ? a : b;
   }
 
@@ -240,7 +240,7 @@ public static <T extends Comparable<? super T>> T max(T a, T b) {
    */
   @ParametricNullness
   public static <T extends @Nullable Object> T max(
-      @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) {
+      @ParametricNullness T a, @ParametricNullness T b, Comparator<? super T> comparator) {
     return (comparator.compare(a, b) >= 0) ? a : b;
   }
 }

guava-tests/test/com/google/common/collect/ComparatorsTest.java

@@ -124,6 +124,29 @@ public void testMinMaxComparator() {
     assertThat(Comparators.max(2, 1, reverse)).isEqualTo(1);
   }
 
+  /**
+   * Fails compilation if the signature of min and max is changed to take {@code Comparator<T>}
+   * instead of {@code Comparator<? super T>}.
+   */
+  public void testMinMaxWithSupertypeComparator() {
+    Comparator<Number> numberComparator =
+        // Can't use Comparator.comparing(Number::intValue) due to Java 7 compatibility.
+        new Comparator<Number>() {
+          @Override
+          public int compare(Number a, Number b) {
+            return a.intValue() - b.intValue();
+          }
+        };
+    Integer comparand1 = 1;
+    Integer comparand2 = 2;
+
+    Integer min = Comparators.min(comparand1, comparand2, numberComparator);
+    Integer max = Comparators.max(comparand1, comparand2, numberComparator);
+
+    assertThat(min).isEqualTo(1);
+    assertThat(max).isEqualTo(2);
+  }
+
   public void testMinMaxComparator_equalInstances() {
     Comparator<Foo> natural = Ordering.natural();
     Comparator<Foo> reverse = Collections.reverseOrder(natural);

guava/src/com/google/common/collect/Comparators.java

@@ -227,7 +227,7 @@ public static <T extends Comparable<? super T>> T min(T a, T b) {
    */
   @ParametricNullness
   public static <T extends @Nullable Object> T min(
-      @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) {
+      @ParametricNullness T a, @ParametricNullness T b, Comparator<? super T> comparator) {
     return (comparator.compare(a, b) <= 0) ? a : b;
   }
 
@@ -265,7 +265,7 @@ public static <T extends Comparable<? super T>> T max(T a, T b) {
    */
   @ParametricNullness
   public static <T extends @Nullable Object> T max(
-      @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) {
+      @ParametricNullness T a, @ParametricNullness T b, Comparator<? super T> comparator) {
     return (comparator.compare(a, b) >= 0) ? a : b;
   }
 }