Improve naming of anonymous/class-in-function Modules (bp #1224) (#1249)

* Better anonymous and class-in-function desiredName

This changes the desired name of a Module to provide non-numeric
naming for anonymous Modules and Modules defined inside function
bodies.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
(cherry picked from commit a69d79f)

* Tests for anonymous/class-in-module desiredName

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
(cherry picked from commit 77d2455)

Author: mergify[bot]

chiselFrontend/src/main/scala/chisel3/Module.scala

@@ -218,10 +218,32 @@ package experimental {
     //
     // Chisel Internals
     //
-    /** Desired name of this module. Override this to give this module a custom, perhaps parametric,
-      * name.
+
+    /** The desired name of this module (which will be used in generated FIRRTL IR or Verilog).
+      *
+      * The name of a module approximates the behavior of the Java Reflection [[`getSimpleName` method
+      * https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html#getSimpleName--]] with some modifications:
+      *
+      * - Anonymous modules will get an `"_Anon"` tag
+      * - Modules defined in functions will use their class name and not a numeric name
+      *
+      * @note If you want a custom or parametric name, override this method.
       */
-    def desiredName: String = this.getClass.getName.split("\\.|\\$").last
+    def desiredName: String = {
+      /* The default module name is derived from the Java reflection derived class name. */
+      val baseName = this.getClass.getName
+
+      /* A sequence of string filters applied to the name */
+      val filters: Seq[String => String] = Seq(
+        ((a: String) => raw"\$$+anon".r.replaceAllIn(a, "_Anon")) // Merge the "$$anon" name with previous name
+      )
+
+      filters
+        .foldLeft(baseName){ case (str, filter) => filter(str) } // 1. Apply filters to baseName
+        .split("\\.|\\$")                                        // 2. Split string at '.' or '$'
+        .filterNot(_.forall(_.isDigit))                          // 3. Drop purely numeric names
+        .last                                                    // 4. Use the last name
+    }
 
     /** Legalized name of this module. */
     final lazy val name = try {

src/test/scala/chiselTests/Module.scala

@@ -158,4 +158,19 @@ class ModuleSpec extends ChiselPropSpec {
     (the [Exception] thrownBy (Driver.elaborate(() => new NullModuleWrapper)))
       .getMessage should include ("desiredName of chiselTests.NullModuleWrapper is null")
   }
+  property("The name of a module in a function should be sane") {
+    def foo = {
+      class Foo1 extends RawModule {
+        assert(name == "Foo1")
+      }
+      new Foo1
+    }
+    Driver.elaborate(() => foo)
+  }
+  property("The name of an anonymous module should include '_Anon'") {
+    trait Foo { this: RawModule =>
+      assert(name.contains("_Anon"))
+    }
+    Driver.elaborate(() => new RawModule with Foo)
+  }
 }