[wpiunits] Change units to track their base unit, instead of their base class (#6342)

Unit objects now have a reference to the base unit from which they're derived. Constructing a unit object without specifying a base unit implicitly signifies that it's its own base unit, eg new Angle(null, 1, "Radian", "rad") would be the base angle unit of radians, while new Angle(Radians, 2 * PI, "Rotation", "R") would be a new angle unit based on radians.

This fixes much of the hacky code surrounding the derived unit types Velocity, Per, and Mult, but is a breaking change for any user code that defines custom unit classes or uses the anonymous unit type.

wpiunits/src/test/java/edu/wpi/first/units/DistanceTest.java

@@ -12,9 +12,10 @@ import org.junit.jupiter.api.Test;
 class DistanceTest {
   @Test
   void testBaseUnitDistancePerTime() {
-    Velocity<Distance> anonBaseUnit = new Distance(1, "D", "d").per(new Time(1, "T", "t"));
+    Velocity<Distance> anonBaseUnit =
+        new Distance(null, 1, "D", "d").per(new Time(null, 1, "T", "t"));
 
-    assertTrue(BaseUnits.Velocity.equivalent(anonBaseUnit));
+    assertTrue(Units.MetersPerSecond.equivalent(anonBaseUnit));
   }
 
   @Test

wpiunits/src/test/java/edu/wpi/first/units/ExampleUnit.java

@@ -9,11 +9,16 @@ class ExampleUnit extends Unit<ExampleUnit> {
     this(baseUnitEquivalent, "Example", "ex");
   }
 
-  ExampleUnit(UnaryFunction toBase, UnaryFunction fromBase, String name, String symbol) {
-    super(ExampleUnit.class, toBase, fromBase, name, symbol);
+  ExampleUnit(
+      ExampleUnit baseUnit,
+      UnaryFunction toBase,
+      UnaryFunction fromBase,
+      String name,
+      String symbol) {
+    super(baseUnit, toBase, fromBase, name, symbol);
   }
 
   ExampleUnit(double baseUnitEquivalent, String name, String symbol) {
-    super(ExampleUnit.class, baseUnitEquivalent, name, symbol);
+    super(null, baseUnitEquivalent, name, symbol);
   }
 }

wpiunits/src/test/java/edu/wpi/first/units/UnitsTest.java

@@ -135,7 +135,7 @@ class UnitsTest {
     assertEquals(9.80665, Gs.of(1).in(MetersPerSecondPerSecond), thresh);
     assertEquals("G", Gs.name());
     assertEquals("G", Gs.symbol());
-    assertEquals(Units.AnonymousBaseUnit, Gs.getUnit());
+    assertEquals(MetersPerSecond, Gs.getUnit());
     assertEquals(Seconds, Gs.getPeriod());
   }
 

wpiunits/src/test/java/edu/wpi/first/units/VelocityTest.java

@@ -20,8 +20,8 @@ import org.junit.jupiter.api.Test;
 class VelocityTest {
   @Test
   void testBaseUnit() {
-    assertTrue(MetersPerSecond.equivalent(BaseUnits.Velocity));
-    assertTrue(Meters.per(Second).equivalent(BaseUnits.Velocity));
+    assertTrue(MetersPerSecond.equivalent(MetersPerSecond));
+    assertTrue(Meters.per(Second).equivalent(MetersPerSecond));
   }
 
   @Test