Fixes to dealing with the export of main

It's surprisingly tricky to deal with 'main' (#19397). This
patch does quite bit of refactoring do to it right. Well,
more-right anyway!

The moving parts are documented in GHC.Tc.Module
   Note [Dealing with main]

Some other oddments:

* Rename tcRnExports to rnExports; no typechecking here!

* rnExports now uses checkNoErrs rather than failIfErrsM;
  the former fails only if rnExports itself finds errors

* Small improvements to tcTyThingCategory, which ultimately
  weren't important to the patch, but I've retained as
  a minor improvement.

1 files changed, 10 insertions, 13 deletions

diff --git a/testsuite/tests/patsyn/should_fail/records-mixing-fields.stderr b/testsuite/tests/patsyn/should_fail/records-mixing-fields.stderr
index 7928c74258..866d1468cd 100644
--- a/testsuite/tests/patsyn/should_fail/records-mixing-fields.stderr
+++ b/testsuite/tests/patsyn/should_fail/records-mixing-fields.stderr
@@ -1,17 +1,14 @@
 
-records-mixing-fields.hs:1:1: error:
-    The IO action ‘main’ is not defined in module ‘Main’
-
 records-mixing-fields.hs:10:14: error:
-    Cannot use a mixture of pattern synonym and record selectors
-    Record selectors defined by ‘MyRec’: qux
-    Pattern synonym selectors defined by ‘HisRec’: f1
-    In the expression: a {f1 = 1, qux = "two"}
-    In an equation for ‘updater1’: updater1 a = a {f1 = 1, qux = "two"}
+    • Cannot use a mixture of pattern synonym and record selectors
+      Record selectors defined by ‘MyRec’: qux
+      Pattern synonym selectors defined by ‘HisRec’: f1
+    • In the expression: a {f1 = 1, qux = "two"}
+      In an equation for ‘updater1’: updater1 a = a {f1 = 1, qux = "two"}
 
 records-mixing-fields.hs:12:14: error:
-    Cannot use a mixture of pattern synonym and record selectors
-    Record selectors defined by ‘MyRec’: foo
-    Pattern synonym selectors defined by ‘HisRec’: f1
-    In the expression: a {f1 = 1, foo = 2}
-    In an equation for ‘updater2’: updater2 a = a {f1 = 1, foo = 2}
+    • Cannot use a mixture of pattern synonym and record selectors
+      Record selectors defined by ‘MyRec’: foo
+      Pattern synonym selectors defined by ‘HisRec’: f1
+    • In the expression: a {f1 = 1, foo = 2}
+      In an equation for ‘updater2’: updater2 a = a {f1 = 1, foo = 2}