Enable Gauge builders to take a subclass of Number (#5601)

This helps with type erasure issues.

Author: s-ste

micrometer-core/src/main/java/io/micrometer/core/instrument/Gauge.java

@@ -53,7 +53,7 @@ static <T> Builder<T> builder(String name, @Nullable T obj, ToDoubleFunction<T>
      * @since 1.1.0
      */
     @Incubating(since = "1.1.0")
-    static Builder<Supplier<Number>> builder(String name, Supplier<Number> f) {
+    static <T extends Number> Builder<Supplier<T>> builder(String name, Supplier<T> f) {
         return new Builder<>(name, f, f2 -> {
             Number val = f2.get();
             return val == null ? Double.NaN : val.doubleValue();

micrometer-core/src/main/java/io/micrometer/core/instrument/MultiGauge.java

@@ -112,7 +112,7 @@ public static Row<Number> of(Tags uniqueTags, Number number) {
             return new Row<>(uniqueTags, number, Number::doubleValue);
         }
 
-        public static Row<Supplier<Number>> of(Tags uniqueTags, Supplier<Number> valueFunction) {
+        public static <T extends Number> Row<Supplier<T>> of(Tags uniqueTags, Supplier<T> valueFunction) {
             return new Row<>(uniqueTags, valueFunction, f -> {
                 Number value = valueFunction.get();
                 return value == null ? Double.NaN : value.doubleValue();

micrometer-core/src/main/java/io/micrometer/core/instrument/TimeGauge.java

@@ -46,7 +46,7 @@ static <T> Builder<T> builder(String name, @Nullable T obj, TimeUnit fUnits, ToD
      * @since 1.7.0
      */
     @Incubating(since = "1.7.0")
-    static Builder<Supplier<Number>> builder(String name, Supplier<Number> f, TimeUnit fUnits) {
+    static <T extends Number> Builder<Supplier<T>> builder(String name, Supplier<T> f, TimeUnit fUnits) {
         return new Builder<>(name, f, fUnits, f2 -> {
             Number val = f2.get();
             return val == null ? Double.NaN : val.doubleValue();

micrometer-core/src/test/java/io/micrometer/core/instrument/MultiGaugeTest.java

@@ -26,6 +26,7 @@
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -93,6 +94,14 @@ void rowGaugesHoldStrongReferences() {
         assertThat(registry.get("colors").tag("color", "red").gauge().value()).isEqualTo(1);
     }
 
+    @Test
+    void rowGaugesCanTakeSubClassOfNumberSuppliers() {
+        final Supplier<Long> supplier = () -> 1L;
+        colorGauges.register(Collections.singletonList(Row.of(Tags.of("color", "red"), supplier)));
+
+        assertThat(registry.get("colors").tag("color", "red").gauge().value()).isEqualTo(1);
+    }
+
     @Test
     void overwrite() {
         testOverwrite();

micrometer-core/src/test/java/io/micrometer/core/instrument/simple/SimpleMeterRegistryTest.java

@@ -22,12 +22,17 @@
 import io.micrometer.core.instrument.step.StepFunctionCounter;
 import io.micrometer.core.instrument.step.StepFunctionTimer;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
 
+import java.math.BigInteger;
 import java.time.Duration;
 import java.util.Arrays;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -165,6 +170,35 @@ void stringRepresentationOfMetersShouldBeOk() {
         sample.stop();
     }
 
+    @ParameterizedTest
+    @MethodSource("getSuppliers")
+    void newGaugeWhenSupplierProvidesSubClassOfNumberShouldReportCorrectly(Supplier<? extends Number> supplier) {
+        Gauge.builder("temperature", supplier).register(registry);
+        assertThat(registry.getMeters()).singleElement().satisfies(meter -> {
+            assertThat(meter.getId().getName()).isEqualTo("temperature");
+            assertThat(meter.measure()).singleElement()
+                .satisfies(measurement -> assertThat(measurement.getValue()).isEqualTo(70));
+        });
+    }
+
+    @ParameterizedTest
+    @MethodSource("getSuppliers")
+    void newTimeGaugeWhenSupplierProvidesSubClassOfNumberShouldReportCorrectly(Supplier<? extends Number> supplier) {
+        TimeGauge.builder("processing.time", supplier, TimeUnit.SECONDS).register(registry);
+        assertThat(registry.getMeters()).singleElement().satisfies(meter -> {
+            assertThat(meter.getId().getName()).isEqualTo("processing.time");
+            assertThat(meter.getId().getBaseUnit()).isEqualTo("seconds");
+            assertThat(meter.measure()).singleElement()
+                .satisfies(measurement -> assertThat(measurement.getValue()).isEqualTo(70));
+        });
+    }
+
+    private static Stream<Supplier<? extends Number>> getSuppliers() {
+        return Stream.of((Supplier<Integer>) () -> 70, (Supplier<Double>) () -> 70.0, (Supplier<Long>) () -> 70L,
+                (Supplier<AtomicInteger>) () -> new AtomicInteger(70),
+                (Supplier<BigInteger>) () -> new BigInteger("70"));
+    }
+
     private SimpleMeterRegistry createRegistry(CountingMode mode) {
         return new SimpleMeterRegistry(new SimpleConfig() {