Hardwire a better unit-id for ghc

Previously, the unit-id of ghc-the-library was fixed as `ghc`.
This was done primarily because the compiler must know the unit-id of
some packages (including ghc) a-priori to define wired-in names.

However, as seen in #20742, a reinstallable `ghc` whose unit-id is fixed
to `ghc` might result in subtle bugs when different ghc's interact.

A good example of this is having GHC_A load a plugin compiled by GHC_B,
where GHC_A and GHC_B are linked to ghc-libraries that are ABI
incompatible. Without a distinction between the unit-id of the ghc library
GHC_A is linked against and the ghc library the plugin it is loading was
compiled against, we can't check compatibility.

This patch gives a slightly better unit-id to ghc (ghc-version) by
(1) Not setting -this-unit-id to ghc, but rather to the new unit-id (modulo stage0)
(2) Adding a definition to `GHC.Settings.Config` whose value is the new unit-id.
    (2.1) `GHC.Settings.Config` is generated by Hadrian
    (2.2) and also by cabal through `compiler/Setup.hs`
This unit-id definition is imported by `GHC.Unit.Types` and used to
set the wired-in unit-id of "ghc", which was previously fixed to "ghc"

The commits following this one will improve the unit-id with a
cabal-style package hash and check compatibility when loading plugins.

Note that we also ensure that ghc's unit key matches unit id both when
hadrian or cabal builds ghc, and in this way we no longer need to add
`ghc` to the WiringMap.

1 files changed, 5 insertions, 1 deletions

diff --git a/testsuite/tests/driver/j-space/jspace.hs b/testsuite/tests/driver/j-space/jspace.hs
index b0c83eb4d1..7f1ef697e8 100644
--- a/testsuite/tests/driver/j-space/jspace.hs
+++ b/testsuite/tests/driver/j-space/jspace.hs
@@ -2,6 +2,7 @@ module Main where
 
 import GHC
 import GHC.Driver.Monad
+import GHC.Driver.Session
 import System.Environment
 import GHC.Driver.Env.Types
 import GHC.Profiling
@@ -25,6 +26,9 @@ initGhcM xs = do
     let cmdOpts = ["-fforce-recomp"] ++ xs
     (df2, leftovers, _) <- parseDynamicFlags (hsc_logger session) df1 (map noLoc cmdOpts)
     setSessionDynFlags df2
+    ghcUnitId <- case lookup "Project Unit Id" (compilerInfo df2) of
+                    Nothing -> fail "failed to find ghc's unit-id in the compiler info"
+                    Just ghcUnitId -> pure ghcUnitId
     ts <- mapM (\s -> guessTarget s Nothing Nothing) $ map unLoc leftovers
     setTargets ts
     _ <- load LoadAllTargets
@@ -36,7 +40,7 @@ initGhcM xs = do
     liftIO $ do
       requestHeapCensus
       performGC
-      [ys] <- filter (isPrefixOf "ghc:GHC.Unit.Module.ModDetails.ModDetails") . lines <$> readFile "jspace.hp"
+      [ys] <- filter (isPrefixOf (ghcUnitId <> ":GHC.Unit.Module.ModDetails.ModDetails")) . lines <$> readFile "jspace.hp"
       let (n :: Int) = read (last (words ys))
       -- The output should be 50 * 8 * word_size (i.e. 3200, or 1600 on 32-bit architectures):
       -- the test contains DEPTH + WIDTH + 2 = 50 modules J, H_0, .., H_DEPTH, W_1, .., W_WIDTH,