Move Chisel3 to SPDX license conventions (#1604)

Change source and other relevant files to use SPDX license
LICENSE file moved from src/ to ./
Changed license file to refer to this per recommendation
using_spdx_license_list_short_identifiers

WARNING: Tests fail with as of yet undiagnosed error
```
[error] Failed: Total 691, Failed 19, Errors 0, Passed 672, Ignored 15
[error] Failed tests:
[error] 	chiselTests.QueueSpec
[error] 	examples.VendingMachineGeneratorSpec
[error] 	chiselTests.HarnessSpec
[error] 	chiselTests.ConnectSpec
[error] 	chiselTests.aop.SelectSpec
[error] 	chiselTests.PopCountSpec
[error] 	chiselTests.CloneModuleSpec
[error] (Test / test) sbt.TestsFailedException: Tests unsuccessful
[error] Total time: 379 s (06:19), completed Sep 30, 2020 12:38:17 AM
sbt:chisel3>
```

44 files changed, 45 insertions, 43 deletions

diff --git a/core/src/main/scala/chisel3/Aggregate.scala b/core/src/main/scala/chisel3/Aggregate.scala
index 4e9a95c1..9ccf7dbb 100644
--- a/core/src/main/scala/chisel3/Aggregate.scala
+++ b/core/src/main/scala/chisel3/Aggregate.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Annotation.scala b/core/src/main/scala/chisel3/Annotation.scala
index b24fa09b..c8ac462d 100644
--- a/core/src/main/scala/chisel3/Annotation.scala
+++ b/core/src/main/scala/chisel3/Annotation.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.experimental
 
diff --git a/core/src/main/scala/chisel3/Assert.scala b/core/src/main/scala/chisel3/Assert.scala
index 310a454d..9a497e1f 100644
--- a/core/src/main/scala/chisel3/Assert.scala
+++ b/core/src/main/scala/chisel3/Assert.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Attach.scala b/core/src/main/scala/chisel3/Attach.scala
index 2736ed65..0e005690 100644
--- a/core/src/main/scala/chisel3/Attach.scala
+++ b/core/src/main/scala/chisel3/Attach.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.experimental
 
diff --git a/core/src/main/scala/chisel3/Bits.scala b/core/src/main/scala/chisel3/Bits.scala
index 0d6ebca7..6bd5a07c 100644
--- a/core/src/main/scala/chisel3/Bits.scala
+++ b/core/src/main/scala/chisel3/Bits.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/BlackBox.scala b/core/src/main/scala/chisel3/BlackBox.scala
index 8493196b..b204e301 100644
--- a/core/src/main/scala/chisel3/BlackBox.scala
+++ b/core/src/main/scala/chisel3/BlackBox.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/BoolFactory.scala b/core/src/main/scala/chisel3/BoolFactory.scala
index 78e73156..787f1e5e 100644
--- a/core/src/main/scala/chisel3/BoolFactory.scala
+++ b/core/src/main/scala/chisel3/BoolFactory.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Clock.scala b/core/src/main/scala/chisel3/Clock.scala
index c5154a8b..edb07908 100644
--- a/core/src/main/scala/chisel3/Clock.scala
+++ b/core/src/main/scala/chisel3/Clock.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/CompileOptions.scala b/core/src/main/scala/chisel3/CompileOptions.scala
index ed410c6e..3dcc25a8 100644
--- a/core/src/main/scala/chisel3/CompileOptions.scala
+++ b/core/src/main/scala/chisel3/CompileOptions.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Data.scala b/core/src/main/scala/chisel3/Data.scala
index bb7efedf..bb45b4d8 100644
--- a/core/src/main/scala/chisel3/Data.scala
+++ b/core/src/main/scala/chisel3/Data.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Element.scala b/core/src/main/scala/chisel3/Element.scala
index fccae9ab..7596bc82 100644
--- a/core/src/main/scala/chisel3/Element.scala
+++ b/core/src/main/scala/chisel3/Element.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Mem.scala b/core/src/main/scala/chisel3/Mem.scala
index ba9dc34b..a60b31ac 100644
--- a/core/src/main/scala/chisel3/Mem.scala
+++ b/core/src/main/scala/chisel3/Mem.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Module.scala b/core/src/main/scala/chisel3/Module.scala
index 194c546c..82a1708e 100644
--- a/core/src/main/scala/chisel3/Module.scala
+++ b/core/src/main/scala/chisel3/Module.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/ModuleAspect.scala b/core/src/main/scala/chisel3/ModuleAspect.scala
index 20793cd7..4e37ab35 100644
--- a/core/src/main/scala/chisel3/ModuleAspect.scala
+++ b/core/src/main/scala/chisel3/ModuleAspect.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/MultiClock.scala b/core/src/main/scala/chisel3/MultiClock.scala
index 718dc989..6a745f14 100644
--- a/core/src/main/scala/chisel3/MultiClock.scala
+++ b/core/src/main/scala/chisel3/MultiClock.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Mux.scala b/core/src/main/scala/chisel3/Mux.scala
index 960424bf..00f2a717 100644
--- a/core/src/main/scala/chisel3/Mux.scala
+++ b/core/src/main/scala/chisel3/Mux.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Num.scala b/core/src/main/scala/chisel3/Num.scala
index 893dd1ce..e1af9bdb 100644
--- a/core/src/main/scala/chisel3/Num.scala
+++ b/core/src/main/scala/chisel3/Num.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Printable.scala b/core/src/main/scala/chisel3/Printable.scala
index 7b730617..006286f9 100644
--- a/core/src/main/scala/chisel3/Printable.scala
+++ b/core/src/main/scala/chisel3/Printable.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Printf.scala b/core/src/main/scala/chisel3/Printf.scala
index fb525b6e..7cbd1918 100644
--- a/core/src/main/scala/chisel3/Printf.scala
+++ b/core/src/main/scala/chisel3/Printf.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/RawModule.scala b/core/src/main/scala/chisel3/RawModule.scala
index 16a2394f..9f0a24d6 100644
--- a/core/src/main/scala/chisel3/RawModule.scala
+++ b/core/src/main/scala/chisel3/RawModule.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/Reg.scala b/core/src/main/scala/chisel3/Reg.scala
index f57281d6..b2b99cc1 100644
--- a/core/src/main/scala/chisel3/Reg.scala
+++ b/core/src/main/scala/chisel3/Reg.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/SIntFactory.scala b/core/src/main/scala/chisel3/SIntFactory.scala
index 35bab7c2..b34c7dde 100644
--- a/core/src/main/scala/chisel3/SIntFactory.scala
+++ b/core/src/main/scala/chisel3/SIntFactory.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/SeqUtils.scala b/core/src/main/scala/chisel3/SeqUtils.scala
index 97bdc505..64904e51 100644
--- a/core/src/main/scala/chisel3/SeqUtils.scala
+++ b/core/src/main/scala/chisel3/SeqUtils.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/StrongEnum.scala b/core/src/main/scala/chisel3/StrongEnum.scala
index 5414ba40..2d372a94 100644
--- a/core/src/main/scala/chisel3/StrongEnum.scala
+++ b/core/src/main/scala/chisel3/StrongEnum.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.experimental
 
diff --git a/core/src/main/scala/chisel3/UIntFactory.scala b/core/src/main/scala/chisel3/UIntFactory.scala
index 864e6cb8..e0f3dc92 100644
--- a/core/src/main/scala/chisel3/UIntFactory.scala
+++ b/core/src/main/scala/chisel3/UIntFactory.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/When.scala b/core/src/main/scala/chisel3/When.scala
index 9e6accbc..048ac08a 100644
--- a/core/src/main/scala/chisel3/When.scala
+++ b/core/src/main/scala/chisel3/When.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/aop/Aspect.scala b/core/src/main/scala/chisel3/aop/Aspect.scala
index 9f10a0dd..59add417 100644
--- a/core/src/main/scala/chisel3/aop/Aspect.scala
+++ b/core/src/main/scala/chisel3/aop/Aspect.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.aop
 
diff --git a/core/src/main/scala/chisel3/core/package.scala b/core/src/main/scala/chisel3/core/package.scala
index 6d5bea13..1da4ba97 100644
--- a/core/src/main/scala/chisel3/core/package.scala
+++ b/core/src/main/scala/chisel3/core/package.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/dontTouch.scala b/core/src/main/scala/chisel3/dontTouch.scala
index a0c5dcc9..0487a567 100644
--- a/core/src/main/scala/chisel3/dontTouch.scala
+++ b/core/src/main/scala/chisel3/dontTouch.scala
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0
+
 package chisel3
 
 import chisel3.experimental.{ChiselAnnotation, annotate, requireIsHardware}
diff --git a/core/src/main/scala/chisel3/experimental/Analog.scala b/core/src/main/scala/chisel3/experimental/Analog.scala
index 37eb578d..df76fd70 100644
--- a/core/src/main/scala/chisel3/experimental/Analog.scala
+++ b/core/src/main/scala/chisel3/experimental/Analog.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.experimental
 
diff --git a/core/src/main/scala/chisel3/experimental/package.scala b/core/src/main/scala/chisel3/experimental/package.scala
index 12631512..ec3f2a79 100644
--- a/core/src/main/scala/chisel3/experimental/package.scala
+++ b/core/src/main/scala/chisel3/experimental/package.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3
 
diff --git a/core/src/main/scala/chisel3/experimental/verification/package.scala b/core/src/main/scala/chisel3/experimental/verification/package.scala
index a983a6fd..5c71bd5f 100644
--- a/core/src/main/scala/chisel3/experimental/verification/package.scala
+++ b/core/src/main/scala/chisel3/experimental/verification/package.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.experimental
 
diff --git a/core/src/main/scala/chisel3/internal/BiConnect.scala b/core/src/main/scala/chisel3/internal/BiConnect.scala
index 49cfeb75..1ee149ee 100644
--- a/core/src/main/scala/chisel3/internal/BiConnect.scala
+++ b/core/src/main/scala/chisel3/internal/BiConnect.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/Binding.scala b/core/src/main/scala/chisel3/internal/Binding.scala
index 95bd40e5..4442c62e 100644
--- a/core/src/main/scala/chisel3/internal/Binding.scala
+++ b/core/src/main/scala/chisel3/internal/Binding.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/Builder.scala b/core/src/main/scala/chisel3/internal/Builder.scala
index 741a2498..3e0362e7 100644
--- a/core/src/main/scala/chisel3/internal/Builder.scala
+++ b/core/src/main/scala/chisel3/internal/Builder.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/Error.scala b/core/src/main/scala/chisel3/internal/Error.scala
index 89d6cc63..003be86f 100644
--- a/core/src/main/scala/chisel3/internal/Error.scala
+++ b/core/src/main/scala/chisel3/internal/Error.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/MonoConnect.scala b/core/src/main/scala/chisel3/internal/MonoConnect.scala
index 7edf6eba..2155894a 100644
--- a/core/src/main/scala/chisel3/internal/MonoConnect.scala
+++ b/core/src/main/scala/chisel3/internal/MonoConnect.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/Namer.scala b/core/src/main/scala/chisel3/internal/Namer.scala
index 0153c0df..1694d71d 100644
--- a/core/src/main/scala/chisel3/internal/Namer.scala
+++ b/core/src/main/scala/chisel3/internal/Namer.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 // This file contains part of the implementation of the naming static annotation system.
 
diff --git a/core/src/main/scala/chisel3/internal/SourceInfo.scala b/core/src/main/scala/chisel3/internal/SourceInfo.scala
index f1130db4..0d6d8eb7 100644
--- a/core/src/main/scala/chisel3/internal/SourceInfo.scala
+++ b/core/src/main/scala/chisel3/internal/SourceInfo.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 // This file contains macros for adding source locators at the point of invocation.
 //
diff --git a/core/src/main/scala/chisel3/internal/firrtl/Converter.scala b/core/src/main/scala/chisel3/internal/firrtl/Converter.scala
index 304ddec6..aefbf8ab 100644
--- a/core/src/main/scala/chisel3/internal/firrtl/Converter.scala
+++ b/core/src/main/scala/chisel3/internal/firrtl/Converter.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal.firrtl
 import chisel3._
diff --git a/core/src/main/scala/chisel3/internal/firrtl/IR.scala b/core/src/main/scala/chisel3/internal/firrtl/IR.scala
index 1783f68f..095c8a05 100644
--- a/core/src/main/scala/chisel3/internal/firrtl/IR.scala
+++ b/core/src/main/scala/chisel3/internal/firrtl/IR.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal.firrtl
 
diff --git a/core/src/main/scala/chisel3/internal/plugin/package.scala b/core/src/main/scala/chisel3/internal/plugin/package.scala
index 6d78b1c3..dd091ccc 100644
--- a/core/src/main/scala/chisel3/internal/plugin/package.scala
+++ b/core/src/main/scala/chisel3/internal/plugin/package.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/internal/prefix.scala b/core/src/main/scala/chisel3/internal/prefix.scala
index fbb1318c..bbe31226 100644
--- a/core/src/main/scala/chisel3/internal/prefix.scala
+++ b/core/src/main/scala/chisel3/internal/prefix.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 package chisel3.internal
 
diff --git a/core/src/main/scala/chisel3/package.scala b/core/src/main/scala/chisel3/package.scala
index 8597b5c7..fb83c9d9 100644
--- a/core/src/main/scala/chisel3/package.scala
+++ b/core/src/main/scala/chisel3/package.scala
@@ -1,4 +1,4 @@
-// See LICENSE for license details.
+// SPDX-License-Identifier: Apache-2.0
 
 import chisel3.internal.firrtl.BinaryPoint