Add interface-stability test for ghc-prim

testsuite/tests/interface-stability/README.mkd

@@ -6,10 +6,19 @@ utility to dump all exported declarations of all exposed modules for the
 following packages:
 
   * `base`
+  * `ghc-experimental`
+  * `template-haskell`
+  * `ghc-prim`
 
 These are compared against the expected exports in the test's corresponding
 `.stdout` file.
 
+Stability expectations vary between these packages: Changes to the
+interface of `base` normally need a [CLC proposal](https://github.com/haskell/core-libraries-committee).
+The interfaces for the other packages listed are tracked primarily to
+prevent _accidental_ changes to them when making changes in
+`ghc-internal`, from which they re-export many things.
+
 
 ## Updating expected output
 

testsuite/tests/interface-stability/all.T

@@ -10,3 +10,4 @@ def check_package(pkg_name):
 check_package('base')
 check_package('ghc-experimental')
 check_package('template-haskell')
+check_package('ghc-prim')

utils/dump-decls/Main.hs

@@ -71,8 +71,7 @@ ignoredModules =
     ]
   where
     unstableModules =
-        [ "GHC.Prim"
-        , "GHC.Conc.POSIX"
+        [ "GHC.Conc.POSIX"
         , "GHC.Conc.IO"
         ]
     platformDependentModules =