Put hole instantiation typechecking in the module graph and fix driver batch mode backpack edges

Backpack instantiations need to be typechecked to make sure that the
arguments fit the parameters. `tcRnInstantiateSignature` checks
instantiations with concrete modules, while `tcRnCheckUnit` checks
instantiations with free holes (signatures in the current modules).

Before this change, it worked that `tcRnInstantiateSignature` was called
after typechecking the argument module, see `HscMain.hsc_typecheck`,
while `tcRnCheckUnit` was called in `unsweep'` where-bound in
`GhcMake.upsweep`. `tcRnCheckUnit` was called once per each
instantiation once all the argument sigs were processed. This was done
with simple "to do" and "already done" accumulators in the fold.
`parUpsweep` did not implement the change.

With this change, `tcRnCheckUnit` instead is associated with its own
node in the `ModuleGraph`. Nodes are now:
```haskell
data ModuleGraphNode
  -- | Instantiation nodes track the instantiation of other units
  -- (backpack dependencies) with the holes (signatures) of the current package.
  = InstantiationNode InstantiatedUnit
  -- | There is a module summary node for each module, signature, and boot module being built.
  | ModuleNode ExtendedModSummary
```
instead of just `ModSummary`; the `InstantiationNode` case is the
instantiation of a unit to be checked. The dependencies of such nodes
are the same "free holes" as was checked with the accumulator before.
Both versions of upsweep on such a node call `tcRnCheckUnit`.

There previously was an `implicitRequirements` function which would
crawl through every non-current-unit module dep to look for all free
holes (signatures) to add as dependencies in `GHC.Driver.Make`. But this
is no good: we shouldn't be looking for transitive anything when
building the graph: the graph should only have immediate edges and the
scheduler takes care that all transitive requirements are met.

So `GHC.Driver.Make` stopped using `implicitRequirements`, and instead
uses a new `implicitRequirementsShallow`, which just returns the
outermost instantiation node (or module name if the immediate dependency
is itself a signature). The signature dependencies are just treated like
any other imported module, but the module ones then go in a list stored
in the `ModuleNode` next to the `ModSummary` as the "extra backpack
dependencies". When `downsweep` creates the mod summaries, it adds this
information too.

------

There is one code quality, and possible correctness thing left: In
addition to `implicitRequirements` there is `findExtraSigImports`, which
says something like "if you are an instantiation argument (you are
substituted or a signature), you need to import its things too".  This
is a little non-local so I am not quite sure how to get rid of it in
`GHC.Driver.Make`, but we probably should eventually.

First though, let's try to make a test case that observes that we don't
do this, lest it actually be unneeded. Until then, I'm happy to leave it
as is.

------

Beside the ability to use `-j`, the other major user-visibile side
effect of this change is that that the --make progress log now includes
"Instantiating" messages for these new nodes. Those also are numbered
like module nodes and count towards the total.

------

Fixes #17188

Updates hackage submomdule

Metric Increase:
    T12425
    T13035

32 files changed, 150 insertions, 24 deletions

diff --git a/testsuite/tests/backpack/should_fail/all.T b/testsuite/tests/backpack/should_fail/all.T
index b9d1eeba3e..5e0d6fdeea 100644
--- a/testsuite/tests/backpack/should_fail/all.T
+++ b/testsuite/tests/backpack/should_fail/all.T
@@ -45,3 +45,7 @@ test('bkpfail46', normal, backpack_compile_fail, [''])
 test('bkpfail47', normal, backpack_compile_fail, [''])
 test('bkpfail48', normal, backpack_compile_fail, [''])
 test('bkpfail49', normal, backpack_compile_fail, [''])
+test('bkpfail50', normal, backpack_compile_fail, [''])
+test('bkpfail51', normal, backpack_compile_fail, [''])
+test('bkpfail52', normal, backpack_compile_fail, [''])
+test('bkpfail53', normal, backpack_compile_fail, [''])
diff --git a/testsuite/tests/backpack/should_fail/bkpfail04.stderr b/testsuite/tests/backpack/should_fail/bkpfail04.stderr
index 0cb8d9cfe0..397cd24851 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail04.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail04.stderr
@@ -3,7 +3,7 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 2] Compiling A[sig]           ( r/A.hsig, nothing )
+  [1 of 4] Compiling A[sig]           ( r/A.hsig, nothing )
 
 bkpfail04.bkp:7:9: error:
     • Type constructor ‘A’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail05.stderr b/testsuite/tests/backpack/should_fail/bkpfail05.stderr
index b231bbdb5b..da996cfb7e 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail05.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail05.stderr
@@ -4,7 +4,8 @@
   Instantiating t-impl
   [1 of 1] Compiling T                ( t-impl/T.hs, bkpfail05.out/t-impl/T.o )
 [3 of 5] Processing p
-  [1 of 1] Compiling H[sig]           ( p/H.hsig, nothing )
+  [1 of 2] Compiling H[sig]           ( p/H.hsig, nothing )
+  [2 of 2] Instantiating h
 [4 of 5] Processing h-impl
   Instantiating h-impl
   [1 of 1] Including t-impl
diff --git a/testsuite/tests/backpack/should_fail/bkpfail07.stderr b/testsuite/tests/backpack/should_fail/bkpfail07.stderr
index 05277035dd..251fd67f0b 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail07.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail07.stderr
@@ -5,7 +5,9 @@
   [2 of 3] Compiling H                ( h/H.hs, nothing )
   [3 of 3] Compiling A[sig]           ( h/A.hsig, nothing )
 [3 of 3] Processing q
-  [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 3] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 3] Instantiating h
+  [3 of 3] Instantiating p
 
 bkpfail07.bkp:6:9: error:
     • Type constructor ‘T’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail09.stderr b/testsuite/tests/backpack/should_fail/bkpfail09.stderr
index b33c3b4b77..de1d100a34 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail09.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail09.stderr
@@ -5,6 +5,8 @@
   Instantiating q
   [1 of 1] Compiling H                ( q/H.hs, bkpfail09.out/q/H.o )
 [3 of 3] Processing r
+  [1 of 3] Compiling H2[sig]          ( r/H2.hsig, nothing )
+  [2 of 3] Instantiating p
 
 Command line argument: -unit-id p[H=H]:0:0: error:
     • ‘H’ is exported by the hsig file, but not exported by the implementing module ‘q:H’
diff --git a/testsuite/tests/backpack/should_fail/bkpfail12.stderr b/testsuite/tests/backpack/should_fail/bkpfail12.stderr
index 0526da438c..f240d2f058 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail12.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail12.stderr
@@ -5,6 +5,8 @@
   Instantiating q
   [1 of 1] Compiling Q                ( q/Q.hs, bkpfail12.out/q/Q.o )
 [3 of 3] Processing r
+  [1 of 3] Compiling H[sig]           ( r/H.hsig, nothing )
+  [2 of 3] Instantiating p
 
 bkpfail12.bkp:8:9: error:
     • Identifier ‘f’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail13.stderr b/testsuite/tests/backpack/should_fail/bkpfail13.stderr
index afd4474f35..13d227a617 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail13.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail13.stderr
@@ -5,6 +5,8 @@
   Instantiating q
   [1 of 1] Compiling QMe              ( q/QMe.hs, bkpfail13.out/q/QMe.o )
 [3 of 3] Processing r
+  [1 of 3] Compiling H[sig]           ( r/H.hsig, nothing )
+  [2 of 3] Instantiating p
 
 bkpfail13.bkp:8:9: error:
     • Identifier ‘f’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail14.stderr b/testsuite/tests/backpack/should_fail/bkpfail14.stderr
index d89e6cab28..401cab2286 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail14.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail14.stderr
@@ -8,6 +8,8 @@
   [2 of 3] Compiling Q                ( q/Q.hs, bkpfail14.out/q/Q.o )
   [3 of 3] Compiling Q2               ( q/Q2.hs, bkpfail14.out/q/Q2.o )
 [3 of 3] Processing r
+  [1 of 3] Compiling H[sig]           ( r/H.hsig, nothing )
+  [2 of 3] Instantiating p
 
 bkpfail14.bkp:9:9: error:
     • Identifier ‘f’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail15.stderr b/testsuite/tests/backpack/should_fail/bkpfail15.stderr
index f32cd6dcf7..cf30efe6f8 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail15.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail15.stderr
@@ -6,7 +6,8 @@
   Instantiating q
   [1 of 1] Compiling Q                ( q/Q.hs, bkpfail15.out/q/Q.o )
 [3 of 3] Processing r
-  [1 of 1] Compiling A[sig]           ( r/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( r/A.hsig, nothing )
+  [2 of 2] Instantiating p
 
 bkpfail15.bkp:8:9: error:
     • Identifier ‘f’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail20.stderr b/testsuite/tests/backpack/should_fail/bkpfail20.stderr
index 4e95695a15..bd450f9f8c 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail20.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail20.stderr
@@ -3,7 +3,7 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 1] Compiling B[sig]           ( r/B.hsig, nothing )
+  [1 of 3] Compiling B[sig]           ( r/B.hsig, nothing )
 
 bkpfail20.bkp:1:1: error:
     • While merging export lists, could not unify Data.STRef.Lazy.newSTRef with GHC.STRef.newSTRef
diff --git a/testsuite/tests/backpack/should_fail/bkpfail21.stderr b/testsuite/tests/backpack/should_fail/bkpfail21.stderr
index 693135bd45..bc40bbc344 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail21.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail21.stderr
@@ -5,9 +5,9 @@
   [1 of 2] Compiling B[sig]           ( q/B.hsig, nothing )
   [2 of 2] Compiling C[sig]           ( q/C.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 3] Compiling H2[sig]          ( r/H2.hsig, nothing )
-  [2 of 3] Compiling H1[sig]          ( r/H1.hsig, nothing )
-  [3 of 3] Compiling H3[sig]          ( r/H3.hsig, nothing )
+  [1 of 5] Compiling H2[sig]          ( r/H2.hsig, nothing )
+  [2 of 5] Compiling H1[sig]          ( r/H1.hsig, nothing )
+  [3 of 5] Compiling H3[sig]          ( r/H3.hsig, nothing )
 
 bkpfail21.bkp:1:1: error:
     • While merging export lists, could not unify {H1.T} with {H2.T}
diff --git a/testsuite/tests/backpack/should_fail/bkpfail28.stderr b/testsuite/tests/backpack/should_fail/bkpfail28.stderr
index 4428da9a41..4850e19240 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail28.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail28.stderr
@@ -3,8 +3,8 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 2] Compiling A[sig]           ( r/A.hsig, nothing )
-  [2 of 2] Compiling R                ( r/R.hs, nothing )
+  [1 of 4] Compiling A[sig]           ( r/A.hsig, nothing )
+  [2 of 4] Compiling R                ( r/R.hs, nothing )
 
 bkpfail28.bkp:18:13: error:
     • Overlapping instances for Show (K a) arising from a use of ‘show’
diff --git a/testsuite/tests/backpack/should_fail/bkpfail29.stderr b/testsuite/tests/backpack/should_fail/bkpfail29.stderr
index dde8978471..dc4f64768a 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail29.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail29.stderr
@@ -3,7 +3,7 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 2] Compiling A[sig]           ( r/A.hsig, nothing )
+  [1 of 4] Compiling A[sig]           ( r/A.hsig, nothing )
 
 bkpfail29.bkp:8:9: error:
     • Cycle in type synonym declarations:
diff --git a/testsuite/tests/backpack/should_fail/bkpfail31.stderr b/testsuite/tests/backpack/should_fail/bkpfail31.stderr
index b5c9bc7b1f..ab599229ad 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail31.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail31.stderr
@@ -1,7 +1,7 @@
 [1 of 4] Processing p
   [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
 [2 of 4] Processing q
-  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 3] Compiling A[sig]           ( q/A.hsig, nothing )
 
 <no location info>: error:
     The identifier T does not exist in the local signature.
diff --git a/testsuite/tests/backpack/should_fail/bkpfail33.stderr b/testsuite/tests/backpack/should_fail/bkpfail33.stderr
index 4da8897b68..addc8d9733 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail33.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail33.stderr
@@ -1,7 +1,7 @@
 [1 of 2] Processing p
   [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
 [2 of 2] Processing q
-  [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
 
 bkpfail33.bkp:5:18: error:
     • Not in scope: type constructor or class ‘T’
diff --git a/testsuite/tests/backpack/should_fail/bkpfail34.stderr b/testsuite/tests/backpack/should_fail/bkpfail34.stderr
index 225e491406..cbe8a1bdbe 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail34.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail34.stderr
@@ -1,7 +1,7 @@
 [1 of 2] Processing p
   [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
 [2 of 2] Processing q
-  [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
 
 <no location info>: error:
     The identifier T does not exist in the local signature.
diff --git a/testsuite/tests/backpack/should_fail/bkpfail35.stderr b/testsuite/tests/backpack/should_fail/bkpfail35.stderr
index cbb2152f7f..893a8dd2ae 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail35.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail35.stderr
@@ -2,7 +2,8 @@
   [1 of 2] Compiling A[sig]           ( p/A.hsig, nothing )
   [2 of 2] Compiling B                ( p/B.hs, nothing )
 [2 of 4] Processing q
-  [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 2] Instantiating p
 [3 of 4] Processing aimpl
   Instantiating aimpl
   [1 of 1] Compiling A                ( aimpl/A.hs, bkpfail35.out/aimpl/A.o )
diff --git a/testsuite/tests/backpack/should_fail/bkpfail36.stderr b/testsuite/tests/backpack/should_fail/bkpfail36.stderr
index cd65f67384..e031625aac 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail36.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail36.stderr
@@ -2,8 +2,8 @@
   [1 of 2] Compiling A[sig]           ( p/A.hsig, nothing )
   [2 of 2] Compiling B[sig]           ( p/B.hsig, nothing )
 [2 of 2] Processing q
-  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
-  [2 of 2] Compiling B[sig]           ( q/B.hsig, nothing )
+  [1 of 3] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 3] Compiling B[sig]           ( q/B.hsig, nothing )
 
 <no location info>: error:
     The identifier T does not exist in the signature for <A>
diff --git a/testsuite/tests/backpack/should_fail/bkpfail38.stderr b/testsuite/tests/backpack/should_fail/bkpfail38.stderr
index df4a1d0483..264e150783 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail38.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail38.stderr
@@ -3,7 +3,7 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 1] Compiling A[sig]           ( r/A.hsig, nothing )
+  [1 of 3] Compiling A[sig]           ( r/A.hsig, nothing )
 
 bkpfail38.bkp:8:9: error:
     • Identifier ‘op’ has conflicting fixities in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail41.stderr b/testsuite/tests/backpack/should_fail/bkpfail41.stderr
index 6cd72dcad1..6f58345fe7 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail41.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail41.stderr
@@ -5,7 +5,8 @@
   Instantiating i
   [1 of 1] Compiling A                ( i/A.hs, bkpfail41.out/i/A.o )
 [3 of 3] Processing r
-  [1 of 1] Compiling B[sig]           ( r/B.hsig, nothing )
+  [1 of 2] Compiling B[sig]           ( r/B.hsig, nothing )
+  [2 of 2] Instantiating p
 
 bkpfail41.bkp:10:9: error:
     • Class ‘C’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail42.stderr b/testsuite/tests/backpack/should_fail/bkpfail42.stderr
index 5b078910f9..aa6857e9a1 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail42.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail42.stderr
@@ -1,7 +1,7 @@
 [1 of 2] Processing p
   [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
 [2 of 2] Processing q
-  [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
 
 bkpfail42.bkp:9:9: error:
     • Type constructor ‘F’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail47.stderr b/testsuite/tests/backpack/should_fail/bkpfail47.stderr
index 0eb58d8ee4..d7f7c174d6 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail47.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail47.stderr
@@ -3,7 +3,7 @@
 [2 of 3] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [3 of 3] Processing r
-  [1 of 1] Compiling A[sig]           ( r/A.hsig, nothing )
+  [1 of 3] Compiling A[sig]           ( r/A.hsig, nothing )
 
 bkpfail47.bkp:9:9: error:
     • Type constructor ‘T’ has conflicting definitions in the module
diff --git a/testsuite/tests/backpack/should_fail/bkpfail48.stderr b/testsuite/tests/backpack/should_fail/bkpfail48.stderr
index cb0740d8bf..27a1f25ac0 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail48.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail48.stderr
@@ -1,7 +1,7 @@
 [1 of 2] Processing q
   [1 of 1] Compiling A[sig]           ( q/A.hsig, nothing )
 [2 of 2] Processing p
-  [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
+  [1 of 2] Compiling A[sig]           ( p/A.hsig, nothing )
 
 bkpfail48.bkp:6:18: error:
     • The export item ‘module Data.Bool’ is not imported
diff --git a/testsuite/tests/backpack/should_fail/bkpfail49.stderr b/testsuite/tests/backpack/should_fail/bkpfail49.stderr
index c2236e5375..27892ec8cf 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail49.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail49.stderr
@@ -1,8 +1,8 @@
 [1 of 2] Processing p
   [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
 [2 of 2] Processing q
-  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
-  [2 of 2] Compiling M                ( q/M.hs, nothing )
+  [1 of 3] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 3] Compiling M                ( q/M.hs, nothing )
 
 bkpfail49.bkp:11:13: error:
     Not in scope: data constructor ‘A.True’
diff --git a/testsuite/tests/backpack/should_fail/bkpfail50.bkp b/testsuite/tests/backpack/should_fail/bkpfail50.bkp
new file mode 100644
index 0000000000..1dda1cb119
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail50.bkp
@@ -0,0 +1,8 @@
+unit p where
+    signature H where
+        data T = T Int
+unit q where
+    dependency p[H=<A>]
+    signature A where
+        data T = T Bool
+-- signatures don't merge
diff --git a/testsuite/tests/backpack/should_fail/bkpfail50.stderr b/testsuite/tests/backpack/should_fail/bkpfail50.stderr
new file mode 100644
index 0000000000..2d4d171ea7
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail50.stderr
@@ -0,0 +1,16 @@
+[1 of 2] Processing p
+  [1 of 1] Compiling H[sig]           ( p/H.hsig, nothing )
+[2 of 2] Processing q
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
+
+bkpfail50.bkp:7:9: error:
+    • Type constructor ‘T’ has conflicting definitions in the module
+      and its hsig file
+      Main module: type T :: *
+                   data T = T Bool
+      Hsig file:  type T :: *
+                  data T = T Int
+      The constructors do not match: The types for ‘T’ differ
+    • while merging the signatures from:
+        • p[H=<A>]:H
+        • ...and the local signature for A
diff --git a/testsuite/tests/backpack/should_fail/bkpfail51.bkp b/testsuite/tests/backpack/should_fail/bkpfail51.bkp
new file mode 100644
index 0000000000..e8cfe5938d
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail51.bkp
@@ -0,0 +1,11 @@
+unit p where
+    signature H where
+        data T = T Int
+    module I(module H) where
+        import H
+unit q where
+    dependency p[H=<A>]
+    signature A where
+        import I
+        type T = H.T
+-- cyclic import
diff --git a/testsuite/tests/backpack/should_fail/bkpfail51.stderr b/testsuite/tests/backpack/should_fail/bkpfail51.stderr
new file mode 100644
index 0000000000..c732e0bcbf
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail51.stderr
@@ -0,0 +1,8 @@
+[1 of 2] Processing p
+  [1 of 2] Compiling H[sig]           ( p/H.hsig, nothing )
+  [2 of 2] Compiling I                ( p/I.hs, nothing )
+[2 of 2] Processing q
+Module imports and instantiations form a cycle:
+        instantiated unit p[H=A]
+        imports module ‘A’ (q/A.hsig)
+  which imports instantiated unit p[H=A]
diff --git a/testsuite/tests/backpack/should_fail/bkpfail52.bkp b/testsuite/tests/backpack/should_fail/bkpfail52.bkp
new file mode 100644
index 0000000000..da5a3c0822
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail52.bkp
@@ -0,0 +1,11 @@
+unit p where
+    signature H where
+        data T = T Int
+unit q where
+    dependency p[H=<A>]
+    module B where
+        data T = T Bool
+    signature A where
+        import qualified B
+        type T = B.T
+-- signatures don't merge
diff --git a/testsuite/tests/backpack/should_fail/bkpfail52.stderr b/testsuite/tests/backpack/should_fail/bkpfail52.stderr
new file mode 100644
index 0000000000..888434e33c
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail52.stderr
@@ -0,0 +1,16 @@
+[1 of 2] Processing p
+  [1 of 1] Compiling H[sig]           ( p/H.hsig, nothing )
+[2 of 2] Processing q
+  [1 of 3] Compiling B                ( q/B.hs, nothing )
+  [2 of 3] Compiling A[sig]           ( q/A.hsig, nothing )
+
+bkpfail52.bkp:10:9: error:
+    • Type constructor ‘T’ has conflicting definitions in the module
+      and its hsig file
+      Main module: type T :: *
+                   type T = B.T
+      Hsig file:  type T :: *
+                  data T = T Int
+    • while merging the signatures from:
+        • p[H=<A>]:H
+        • ...and the local signature for A
diff --git a/testsuite/tests/backpack/should_fail/bkpfail53.bkp b/testsuite/tests/backpack/should_fail/bkpfail53.bkp
new file mode 100644
index 0000000000..47e7c4593c
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail53.bkp
@@ -0,0 +1,21 @@
+
+unit p where
+    signature H where
+        data T = T Int
+    module I(module H) where
+        import H
+        x :: Int -> T
+        x = T
+unit q where
+    dependency p[H=<A>]
+    module B where
+        data T = T Bool
+    signature A where
+        import qualified B
+        type T = B.T
+    module C where
+        import qualified B
+        import qualified I
+        x :: Int -> B.T
+        x = I.x
+-- signatures don't merge
diff --git a/testsuite/tests/backpack/should_fail/bkpfail53.stderr b/testsuite/tests/backpack/should_fail/bkpfail53.stderr
new file mode 100644
index 0000000000..b694bc57ff
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail53.stderr
@@ -0,0 +1,17 @@
+[1 of 2] Processing p
+  [1 of 2] Compiling H[sig]           ( p/H.hsig, nothing )
+  [2 of 2] Compiling I                ( p/I.hs, nothing )
+[2 of 2] Processing q
+  [1 of 4] Compiling B                ( q/B.hs, nothing )
+  [2 of 4] Compiling A[sig]           ( q/A.hsig, nothing )
+
+bkpfail53.bkp:15:9: error:
+    • Type constructor ‘T’ has conflicting definitions in the module
+      and its hsig file
+      Main module: type T :: *
+                   type T = B.T
+      Hsig file:  type T :: *
+                  data T = T Int
+    • while merging the signatures from:
+        • p[H=<A>]:H
+        • ...and the local signature for A