Restore 'It is a member of hidden package' message.

See comment in Packages for more details.

Fixes #14717.

Signed-off-by: Edward Z. Yang <ezyang@fb.com>

Test Plan: validate

Reviewers: snoyberg, taylorfausak, bgamari

Reviewed By: snoyberg, taylorfausak, bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #14717

Differential Revision: https://phabricator.haskell.org/D4376

4 files changed, 37 insertions, 3 deletions

diff --git a/compiler/main/Packages.hs b/compiler/main/Packages.hs
index 14407be418..e8e9032761 100644
--- a/compiler/main/Packages.hs
+++ b/compiler/main/Packages.hs
@@ -1596,8 +1596,35 @@ mkModuleToPkgConfAll
   -> VisibilityMap
   -> ModuleToPkgConfAll
 mkModuleToPkgConfAll dflags pkg_db vis_map =
-    Map.foldlWithKey extend_modmap emptyMap vis_map
+    -- What should we fold on?  Both situations are awkward:
+    --
+    --    * Folding on the visibility map means that we won't create
+    --      entries for packages that aren't mentioned in vis_map
+    --      (e.g., hidden packages, causing #14717)
+    --
+    --    * Folding on pkg_db is awkward because if we have an
+    --      Backpack instantiation, we need to possibly add a
+    --      package from pkg_db multiple times to the actual
+    --      ModuleToPkgConfAll.  Also, we don't really want
+    --      definite package instantiations to show up in the
+    --      list of possibilities.
+    --
+    -- So what will we do instead?  We'll extend vis_map with
+    -- entries for every definite (for non-Backpack) and
+    -- indefinite (for Backpack) package, so that we get the
+    -- hidden entries we need.
+    Map.foldlWithKey extend_modmap emptyMap vis_map_extended
  where
+  vis_map_extended = Map.union vis_map {- preferred -} default_vis
+
+  default_vis = Map.fromList
+                  [ (packageConfigId pkg, mempty)
+                  | pkg <- eltsUDFM (unPackageConfigMap pkg_db)
+                  -- Exclude specific instantiations of an indefinite
+                  -- package
+                  , indefinite pkg || null (instantiatedWith pkg)
+                  ]
+
   emptyMap = Map.empty
   sing pk m _ = Map.singleton (mkModule pk m)
   addListTo = foldl' merge
diff --git a/testsuite/tests/package/package07e.stderr b/testsuite/tests/package/package07e.stderr
index a446a47247..9ca835f7ac 100644
--- a/testsuite/tests/package/package07e.stderr
+++ b/testsuite/tests/package/package07e.stderr
@@ -1,16 +1,20 @@
 
 package07e.hs:2:1: error:
     Could not find module ‘MyHsTypes’
+    Perhaps you meant HsTypes (needs flag -package-key ghc-8.5)
     Use -v to see a list of the files searched for.
 
 package07e.hs:3:1: error:
     Could not find module ‘HsTypes’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
 
 package07e.hs:4:1: error:
     Could not find module ‘HsUtils’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
 
 package07e.hs:5:1: error:
     Could not find module ‘UniqFM’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
diff --git a/testsuite/tests/package/package08e.stderr b/testsuite/tests/package/package08e.stderr
index 3d8d2321b7..5992a4ca49 100644
--- a/testsuite/tests/package/package08e.stderr
+++ b/testsuite/tests/package/package08e.stderr
@@ -1,16 +1,20 @@
 
 package08e.hs:2:1: error:
     Could not find module ‘MyHsTypes’
+    Perhaps you meant HsTypes (needs flag -package-key ghc-8.5)
     Use -v to see a list of the files searched for.
 
 package08e.hs:3:1: error:
     Could not find module ‘HsTypes’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
 
 package08e.hs:4:1: error:
     Could not find module ‘HsUtils’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
 
 package08e.hs:5:1: error:
     Could not find module ‘UniqFM’
+    It is a member of the hidden package ‘ghc-8.5’.
     Use -v to see a list of the files searched for.
diff --git a/testsuite/tests/plugins/T11244.stderr b/testsuite/tests/plugins/T11244.stderr
index f489103f28..30c8c5b127 100644
--- a/testsuite/tests/plugins/T11244.stderr
+++ b/testsuite/tests/plugins/T11244.stderr
@@ -1,4 +1,3 @@
 <command line>: Could not find module ‘RuleDefiningPlugin’
-Perhaps you meant
-  RuleDefiningPlugin (from rule-defining-plugin-0.1)
+It is a member of the hidden package ‘rule-defining-plugin-0.1’.
 Use -v to see a list of the files searched for.