Simplify bindLHsTyVarBndrs and bindHsQTyVarswip/simply-bind-tyvars

Both `bindLHsTyVarBndrs` and `bindHsQTyVars` take two separate
`Maybe` arguments, which I find terribly confusing. Thankfully, it's
possible to remove one `Maybe` argument from each of these functions,
which this patch accomplishes:

* `bindHsQTyVars` takes a `Maybe SDoc` argument, which is `Just` if
  GHC should warn about any of the quantified type variables going
  unused. However, every call site uses `Nothing` in practice. This
  makes sense, since it doesn't really make sense to warn about
  unused type variables bound by an `LHsQTyVars`. For instance, you
  wouldn't warn about the `a` in `data Proxy a = Proxy` going unused.

  As a result, I simply remove this `Maybe SDoc` argument altogether.
* `bindLHsTyVarBndrs` also takes a `Maybe SDoc` argument for the same
  reasons that `bindHsQTyVars` took one. To make things more
  confusing, however, `bindLHsTyVarBndrs` also takes a separate
  `HsDocContext` argument, which is pretty-printed (to an `SDoc`) in
  warnings and error messages.

  In practice, the `Maybe SDoc` and the `HsDocContext` often contain
  the same text. See the call sites for `bindLHsTyVarBndrs` in
  `rnFamInstEqn` and `rnConDecl`, for instance. There are only a
  handful of call sites where the text differs between the
  `Maybe SDoc` and `HsDocContext` arguments:

  * In `rnHsRuleDecl`, where the `Maybe SDoc` says "`In the rule`"
    and the `HsDocContext` says "`In the transformation rule`".
  * In `rnHsTyKi`/`rn_ty`, where the `Maybe SDoc` says
    "`In the type`" but the `HsDocContext` is inhereted from the
    surrounding context (e.g., if `rnHsTyKi` were called on a
    top-level type signature, the `HsDocContext` would be
    "`In the type signature`" instead)

  In both cases, warnings/error messages arguably _improve_ by
  unifying making the `Maybe SDoc`'s text match that of the
  `HsDocContext`. As a result, I decided to remove the `Maybe SDoc`
  argument to `bindLHsTyVarBndrs` entirely and simply reuse the text
  from the `HsDocContext`. (I decided to change the phrase
  "transformation rule" to "rewrite rule" while I was in the area.)

  The `Maybe SDoc` argument has one other purpose: signaling when to
  emit "`Unused quantified type variable`" warnings. To recover this
  functionality, I replaced the `Maybe SDoc` argument with a
  boolean-like `WarnUnusedForalls` argument. The only
  `bindLHsTyVarBndrs` call site that chooses _not_ to emit these
  warnings in `bindHsQTyVars`.

6 files changed, 9 insertions, 9 deletions

diff --git a/testsuite/tests/dependent/should_fail/T16326_Fail10.stderr b/testsuite/tests/dependent/should_fail/T16326_Fail10.stderr
index 4ef380e5ba..44a0d34a33 100644
--- a/testsuite/tests/dependent/should_fail/T16326_Fail10.stderr
+++ b/testsuite/tests/dependent/should_fail/T16326_Fail10.stderr
@@ -4,4 +4,4 @@ T16326_Fail10.hs:12:18: error:
         forall a -> a -> a
       (GHC does not yet support this)
     • In the type signature for ‘x’: forall a -> a -> a
-      When checking the transformation rule "flurmp"
+      When checking the rewrite rule "flurmp"
diff --git a/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr b/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
index 0a575c9bb3..5852074450 100644
--- a/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
+++ b/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
@@ -1,4 +1,4 @@
 
 ExplicitForAllRules1.hs:49:31: warning: [-Wunused-foralls (in -Wextra)]
     Unused quantified type variable ‘b’
-    in the rule "example7"
+    In the rewrite rule "example7"
diff --git a/testsuite/tests/rename/should_compile/T5331.stderr b/testsuite/tests/rename/should_compile/T5331.stderr
index fb27e64af1..d57daceb0a 100644
--- a/testsuite/tests/rename/should_compile/T5331.stderr
+++ b/testsuite/tests/rename/should_compile/T5331.stderr
@@ -9,4 +9,4 @@ T5331.hs:11:16: warning: [-Wunused-foralls (in -Wextra)]
 
 T5331.hs:13:13: warning: [-Wunused-foralls (in -Wextra)]
     Unused quantified type variable ‘a’
-    In the type ‘forall a. Int’
+    In the type signature for ‘f’
diff --git a/testsuite/tests/safeHaskell/ghci/p14.stderr b/testsuite/tests/safeHaskell/ghci/p14.stderr
index 65baafe716..736e8b448c 100644
--- a/testsuite/tests/safeHaskell/ghci/p14.stderr
+++ b/testsuite/tests/safeHaskell/ghci/p14.stderr
@@ -1,6 +1,6 @@
 
 <interactive>:9:25: error:
-    No instance for (Num a) arising from a use of ‘f’
-    Possible fix: add (Num a) to the context of the RULE "id/Int"
-    In the expression: f
-    When checking the transformation rule "id/Int"
+    • No instance for (Num a) arising from a use of ‘f’
+      Possible fix: add (Num a) to the context of the RULE "id/Int"
+    • In the expression: f
+      When checking the rewrite rule "id/Int"
diff --git a/testsuite/tests/typecheck/should_compile/T10072.stderr b/testsuite/tests/typecheck/should_compile/T10072.stderr
index 71a93c9573..994a03f903 100644
--- a/testsuite/tests/typecheck/should_compile/T10072.stderr
+++ b/testsuite/tests/typecheck/should_compile/T10072.stderr
@@ -7,4 +7,4 @@ T10072.hs:3:31: error:
       To use the inferred type, enable PartialTypeSignatures
     • In the type ‘a -> _’
       In the type signature for ‘f’: a -> _
-      When checking the transformation rule "map/empty"
+      When checking the rewrite rule "map/empty"
diff --git a/testsuite/tests/typecheck/should_fail/T5853.stderr b/testsuite/tests/typecheck/should_fail/T5853.stderr
index 6fd62bb79b..5d42625796 100644
--- a/testsuite/tests/typecheck/should_fail/T5853.stderr
+++ b/testsuite/tests/typecheck/should_fail/T5853.stderr
@@ -9,7 +9,7 @@ T5853.hs:15:52: error:
         bound by the RULE "map/map" at T5853.hs:15:2-57
       NB: ‘Subst’ is a non-injective type family
     • In the expression: (f . g) <$> xs
-      When checking the transformation rule "map/map"
+      When checking the rewrite rule "map/map"
     • Relevant bindings include
         f :: Elem fa -> b (bound at T5853.hs:15:19)
         g :: a -> Elem fa (bound at T5853.hs:15:21)