From 9c064dac3528fda98fd29ee93a03ae24e87d17bb Mon Sep 17 00:00:00 2001
From: Andreas Herrmann <42969706+aherrmann-da@users.noreply.github.com>
Date: Mon, 26 Jul 2021 13:45:52 +0200
Subject: [PATCH] Allow imports of internal modules (#10397)

* Allow imports of internal modules

changelog_begin
- [Daml Compiler] Imports of internal modules from stable packages are
  no longer illegal. Previously, the compiler raised an error when it
  encountered imports of internal modules such as
  `DA.Internal.Template`. Such imports are now accepted by the compiler.
  Note, however, that internal modules are still not part of the stable
  API. Fixes https://github.com/digital-asset/daml/issues/10379
changelog_end

* ~unstable~

https://github.com/digital-asset/daml/pull/10397#discussion_r676485891

Co-authored-by: Andreas Herrmann <andreas.herrmann@tweag.io>
---
 .../damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs | 1 +
 compiler/damlc/daml-preprocessor/BUILD.bazel             | 2 ++
 .../damlc/daml-preprocessor/src/DA/Daml/Preprocessor.hs  | 9 ++++++++-
 compiler/damlc/tests/daml-test-files/InternalImport.daml | 5 +++--
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/compiler/damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs b/compiler/damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs
index 93d33b8622d7..5dce65bbbdf7 100644
--- a/compiler/damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs
+++ b/compiler/damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs
@@ -75,6 +75,7 @@
 
 module DA.Daml.LFConversion
     ( convertModule
+    , convertModuleName
     , sourceLocToRange
     , convertRationalBigNumeric -- exposed for festing
     , runConvertM -- exposed for testing
diff --git a/compiler/damlc/daml-preprocessor/BUILD.bazel b/compiler/damlc/daml-preprocessor/BUILD.bazel
index 96ec5cb5bda8..3d897af34814 100644
--- a/compiler/damlc/daml-preprocessor/BUILD.bazel
+++ b/compiler/damlc/daml-preprocessor/BUILD.bazel
@@ -35,6 +35,8 @@ da_haskell_library(
         "//compiler/daml-lf-ast",
         "//compiler/daml-lf-proto",
         "//compiler/daml-lf-tools",
+        "//compiler/damlc/daml-lf-conversion",
+        "//compiler/damlc/stable-packages:stable-packages-lib",
         "//libs-haskell/bazel-runfiles",
         "//libs-haskell/da-hs-base",
     ],
diff --git a/compiler/damlc/daml-preprocessor/src/DA/Daml/Preprocessor.hs b/compiler/damlc/daml-preprocessor/src/DA/Daml/Preprocessor.hs
index 30f343230bdd..9c97621fba73 100644
--- a/compiler/damlc/daml-preprocessor/src/DA/Daml/Preprocessor.hs
+++ b/compiler/damlc/daml-preprocessor/src/DA/Daml/Preprocessor.hs
@@ -8,9 +8,11 @@ module DA.Daml.Preprocessor
   , noPreprocessor
   ) where
 
+import           DA.Daml.LFConversion (convertModuleName)
 import           DA.Daml.Preprocessor.Records
 import           DA.Daml.Preprocessor.Generics
 import           DA.Daml.Preprocessor.EnumType
+import           DA.Daml.StablePackages (stablePackageByModuleName)
 
 import Development.IDE.Types.Options
 import qualified "ghc-lib" GHC
@@ -47,6 +49,11 @@ isInternal (GHC.moduleNameString -> x)
       , "DA.Time.Types"
       ]
 
+isUnstableInternal :: GHC.ModuleName -> Bool
+isUnstableInternal moduleName =
+  isInternal moduleName &&
+    convertModuleName moduleName `Map.notMember` stablePackageByModuleName
+
 preprocessorExceptions :: Set.Set GHC.ModuleName
 preprocessorExceptions = Set.fromList $ map GHC.mkModuleName
     -- These modules need to import internal modules.
@@ -164,7 +171,7 @@ checkModuleName (GHC.L _ m)
 checkImports :: GHC.ParsedSource -> [(GHC.SrcSpan, String)]
 checkImports x =
     [ (ss, "Import of internal module " ++ GHC.moduleNameString m ++ " is not allowed.")
-    | GHC.L ss GHC.ImportDecl{ideclName=GHC.L _ m} <- GHC.hsmodImports $ GHC.unLoc x, isInternal m]
+    | GHC.L ss GHC.ImportDecl{ideclName=GHC.L _ m} <- GHC.hsmodImports $ GHC.unLoc x, isUnstableInternal m]
 
 -- | Emit a warning if the "daml 1.2" version header is present.
 checkDamlHeader :: GHC.ParsedSource -> [(GHC.SrcSpan, String)]
diff --git a/compiler/damlc/tests/daml-test-files/InternalImport.daml b/compiler/damlc/tests/daml-test-files/InternalImport.daml
index 630b3ed96877..acb603747f0a 100644
--- a/compiler/damlc/tests/daml-test-files/InternalImport.daml
+++ b/compiler/damlc/tests/daml-test-files/InternalImport.daml
@@ -1,9 +1,10 @@
 -- Copyright (c) 2020, Digital Asset (Switzerland) GmbH and/or its affiliates.
 -- All rights reserved.
 
--- @ERROR range=9:1-9:28; Import of internal module DA.Internal.Template is not allowed.
+-- @ERROR range=10:1-10:39; Import of internal module DA.Internal.RebindableSyntax is not allowed.
 
 
 module InternalImport where
 
-import DA.Internal.Template
+import DA.Internal.Template ()
+import DA.Internal.RebindableSyntax ()