Make requireTypeEquivalent public and add context message (backport #4243)

core/src/main/scala/chisel3/Data.scala

@@ -606,15 +606,18 @@ abstract class Data extends HasId with NamedComponent with SourceInfoDoc {
 
   /** Require that two things are type equivalent, and if they are not, print a helpful error message as
     * to why not.
+    *
+    * @param that the Data to compare to for type equivalence
+    * @param message if they are not type equivalent, contextual message to add to the exception thrown
     */
-  private[chisel3] def requireTypeEquivalent(that: Data): Unit = {
+  private[chisel3] def requireTypeEquivalent(that: Data, message: String = ""): Unit = {
     require(
       this.typeEquivalent(that), {
         val reason = this
           .findFirstTypeMismatch(that, strictTypes = true, strictWidths = true, strictProbeInfo = true)
           .map(s => s"\nbecause $s")
           .getOrElse("")
-        s"$this is not typeEquivalent to $that$reason"
+        s"$message$this is not typeEquivalent to $that$reason"
       }
     )
   }

core/src/main/scala/chisel3/reflect/DataMirror.scala

@@ -105,6 +105,20 @@ object DataMirror {
     */
   def checkTypeEquivalence(x: Data, y: Data): Boolean = x.typeEquivalent(y)
 
+  /** Require that two things are type equivalent
+    *
+    * If they are not, print a helpful error message as
+    * to why not.
+    *
+    * Requires structural, alignment, width, probe, color type equivalent
+    * @param x First Chisel type
+    * @param y Second chisel type
+    * @param message if they are not type equivalent, contextual message to add to the exception thrown
+    */
+  def requireTypeEquivalent(x: Data, y: Data, message: String = ""): Unit = {
+    x.requireTypeEquivalent(y, message)
+  }
+
   /** Check if two Chisel types have the same alignments for all matching members
     *
     * This means that for matching members in Aggregates, they must have matching member alignments relative to the parent type

src/test/scala/chisel3/TypeEquivalenceSpec.scala

@@ -17,6 +17,14 @@ object TypeEquivalenceSpec {
     val c = if (hasC) Some(UInt(8.W)) else None
   }
 
+  class FooParent(hasC: Boolean) extends Bundle {
+    val foo = new Foo(hasC)
+  }
+
+  class FooGrandparent(hasC: Boolean) extends Bundle {
+    val bar = new FooParent(hasC)
+  }
+
   class Bar(bWidth: Int = 8) extends Bundle {
     val a = UInt(8.W)
     val b = UInt(bWidth.W)
@@ -340,4 +348,22 @@ class TypeEquivalenceSpec extends AnyFlatSpec {
     )
   }
 
+  behavior.of("Data.requireTypeEquivalent")
+
+  it should "have a good user message if it fails for wrong scala type" in {
+    val result = the[IllegalArgumentException] thrownBy {
+      Bool().requireTypeEquivalent(UInt(1.W), "This test should fail, because: ")
+    }
+    result.getMessage should include("This test should fail, because: Bool is not typeEquivalent to UInt<1>")
+  }
+
+  it should "have a good user message if it fails for mismatched bundles" in {
+    val result = the[IllegalArgumentException] thrownBy {
+      (new FooGrandparent(true)).requireTypeEquivalent(new FooGrandparent(false), "This test should fail, because: ")
+    }
+    result.getMessage should include("This test should fail, because:")
+    // Also says 'FooGrandparent$1 is not typeEquivalent to FooGrandparent$1' which isn't terribly interesting to match on
+    result.getMessage should include(".bar.foo.c: Dangling field on Left")
+  }
+
 }