Check for Vec subaccess in NamedComponent and throw a nicer error. (backport #2907) (#2928)

* Check for Vec subaccess in NamedComponent and throw a nicer error. (#2907)

This would previously end up throwing an exception later, when trying
to create a component name and realizing that it was invalid. Instead,
this detects Vec subaccesses early, and gives a more precise error and
suggestion.

(cherry picked from commit d8c30961c7b293ee19024a487698630367ee71c6)

# Conflicts:
#	core/src/main/scala/chisel3/internal/Builder.scala

* Resolve backport conflicts

Co-authored-by: Mike Urbach <mikeurbach@gmail.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/src/test/scala/chiselTests/VecToTargetSpec.scala b/src/test/scala/chiselTests/VecToTargetSpec.scala
new file mode 100644
index 00000000..20c6f306
--- /dev/null
+++ b/src/test/scala/chiselTests/VecToTargetSpec.scala
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package chiselTests
+
+import chisel3._
+import chisel3.stage.ChiselStage
+
+trait VecToTargetSpecUtils extends Utils {
+  this: ChiselFunSpec =>
+
+  class Foo extends RawModule {
+    val vec = IO(Input(Vec(4, Bool())))
+
+    // Index a Vec with a Scala literal.
+    val scalaLit = 0
+    val vecSubaccessScalaLit = vec(scalaLit)
+
+    // Index a Vec with a Chisel literal.
+    val chiselLit = 0.U
+    val vecSubaccessChiselLit = vec(chiselLit)
+
+    // Index a Vec with a node.
+    val node = IO(Input(UInt(2.W)))
+    val vecSubaccessNode = vec(node)
+
+    // Put an otherwise un-targetable Vec subaccess into a temp.
+    val vecSubaccessTmp = WireInit(vecSubaccessNode)
+  }
+
+  val expectedError = "You cannot target Vec subaccess:"
+
+  def conversionSucceeds(data: InstanceId) = {
+    describe(".toTarget") {
+      it("should convert successfully") {
+        data.toTarget
+      }
+    }
+
+    describe(".toNamed") {
+      it("should convert successfully") {
+        data.toNamed
+      }
+    }
+  }
+
+  def conversionFails(data: InstanceId) = {
+    describe(".toTarget") {
+      it("should fail to convert with a useful error message") {
+        (the[ChiselException] thrownBy extractCause[ChiselException] {
+          data.toTarget
+        }).getMessage should include(expectedError)
+      }
+    }
+
+    describe(".toNamed") {
+      it("should fail to convert with a useful error message") {
+        (the[ChiselException] thrownBy extractCause[ChiselException] {
+          data.toNamed
+        }).getMessage should include(expectedError)
+      }
+    }
+  }
+}
+
+class VecToTargetSpec extends ChiselFunSpec with VecToTargetSpecUtils {
+  describe("Vec subaccess") {
+    var foo: Foo = null
+    ChiselStage.elaborate { foo = new Foo; foo }
+
+    describe("with a Scala literal") {
+      (it should behave).like(conversionSucceeds(foo.vecSubaccessScalaLit))
+    }
+
+    describe("with a Chisel literal") {
+      (it should behave).like(conversionFails(foo.vecSubaccessChiselLit))
+    }
+
+    describe("with a Node") {
+      (it should behave).like(conversionFails(foo.vecSubaccessNode))
+    }
+
+    describe("with an un-targetable construct that is assigned to a temporary") {
+      (it should behave).like(conversionSucceeds(foo.vecSubaccessTmp))
+    }
+  }
+}