Implement -hide-all-plugin-packages and -plugin-package(-id), fixing #11244

Summary:
The basic idea is that we have a new set of "exposed modules"
which are /only/ used for plugins, i.e. -fplugin Foo and
--frontend Foo.  You can interact with this namespace
using the flags -plugin-package-id and -plugin-package.
By default, this namespace contains all modules in the
user namespace (as before), but you can toggle that using
-hide-all-plugin-packages.

There is one nasty hack: GhcMake respects -fplugin in
GHC_OPTIONS to make local plugins work correctly.  It also
bails out of you have an import of a module which doesn't
exist locally or in the package database.  The upshot is
that we need to be sure to check in the plugin modules
too, so we don't give a spurious failure when a plugin
is in the plugin namespace but not the main namespace.
A better way to fix this would be to distinguish between
plugin and normal dependencies in ModSummary.

I cheated a little and tweaked a few existing plugins
tests to exercise the new code paths.

TODO: Documentation

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: bgamari, austin, simonpj, duncan

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1661

GHC Trac Issues: #11244

1 files changed, 25 insertions, 2 deletions

diff --git a/compiler/main/Finder.hs b/compiler/main/Finder.hs
index c6bbd7583f..dddc09a6eb 100644
--- a/compiler/main/Finder.hs
+++ b/compiler/main/Finder.hs
@@ -10,6 +10,7 @@ module Finder (
     flushFinderCaches,
     FindResult(..),
     findImportedModule,
+    findPluginModule,
     findExactModule,
     findHomeModule,
     findExposedPackageModule,
@@ -89,7 +90,7 @@ lookupFinderCache ref key = do
    return $! lookupModuleEnv c key
 
 -- -----------------------------------------------------------------------------
--- The two external entry points
+-- The three external entry points
 
 -- | Locate a module that was imported by the user.  We have the
 -- module's name, and possibly a package name.  Without a package
@@ -112,6 +113,16 @@ findImportedModule hsc_env mod_name mb_pkg =
                     `orIfNotFound`
                     findExposedPackageModule hsc_env mod_name Nothing
 
+-- | Locate a plugin module requested by the user, for a compiler
+-- plugin.  This consults the same set of exposed packages as
+-- 'findImportedModule', unless @-hide-all-plugin-packages@ or
+-- @-plugin-package@ are specified.
+findPluginModule :: HscEnv -> ModuleName -> IO FindResult
+findPluginModule hsc_env mod_name =
+  findHomeModule hsc_env mod_name
+  `orIfNotFound`
+  findExposedPluginPackageModule hsc_env mod_name
+
 -- | Locate a specific 'Module'.  The purpose of this function is to
 -- create a 'ModLocation' for a given 'Module', that is to find out
 -- where the files associated with this module live.  It is used when
@@ -160,7 +171,19 @@ homeSearchCache hsc_env mod_name do_this = do
 findExposedPackageModule :: HscEnv -> ModuleName -> Maybe FastString
                          -> IO FindResult
 findExposedPackageModule hsc_env mod_name mb_pkg
-  = case lookupModuleWithSuggestions (hsc_dflags hsc_env) mod_name mb_pkg of
+  = findLookupResult hsc_env
+  $ lookupModuleWithSuggestions
+        (hsc_dflags hsc_env) mod_name mb_pkg
+
+findExposedPluginPackageModule :: HscEnv -> ModuleName
+                               -> IO FindResult
+findExposedPluginPackageModule hsc_env mod_name
+  = findLookupResult hsc_env
+  $ lookupPluginModuleWithSuggestions
+        (hsc_dflags hsc_env) mod_name Nothing
+
+findLookupResult :: HscEnv -> LookupResult -> IO FindResult
+findLookupResult hsc_env r = case r of
      LookupFound m pkg_conf ->
        findPackageModule_ hsc_env m pkg_conf
      LookupMultiple rs ->