[Git][ghc/ghc][master] Correct -Wpartial-fields warning to say "Definition" rather than "Use"

[Marge Bot (@marge-bot)]

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
6c469bd2 by Adam Gundry at 2024-07-04T11:10:33-04:00
Correct -Wpartial-fields warning to say "Definition" rather than "Use"

Fixes #24710.  The message and documentation for `-Wpartial-fields` were
misleading as (a) the warning occurs at definition sites rather than use
sites, and (b) the warning relates to the definition of a field independently
of the selector function (e.g. because record updates are also partial).

- - - - -


5 changed files:

- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Errors/Types.hs
- docs/users_guide/using-warnings.rst
- testsuite/tests/overloadedrecflds/should_fail/DRFPartialFields.stderr
- testsuite/tests/typecheck/should_compile/T7169.stderr


Changes:

=====================================
compiler/GHC/Tc/Errors/Ppr.hs
=====================================
@@ -1501,8 +1501,9 @@ instance Diagnostic TcRnMessage where
       text "You may define an abstract closed type family" $$
       text "only in a .hs-boot file"
     TcRnPartialFieldSelector fld -> mkSimpleDecorated $
-      sep [text "Use of partial record field selector" <> colon,
-           nest 2 $ quotes (ppr (occName fld))]
+      vcat [ sep [ text "Definition of partial record field" <> colon
+                 , nest 2 $ quotes (ppr (occName fld)) ]
+           , text "Record selection and update using this field will be partial." ]
     TcRnHasFieldResolvedIncomplete name -> mkSimpleDecorated $
       text "The invocation of `getField` on the record field" <+> quotes (ppr name)
       <+> text "may produce an error since it is not defined for all data constructors"


=====================================
compiler/GHC/Tc/Errors/Types.hs
=====================================
@@ -3503,7 +3503,7 @@ data TcRnMessage where
   -}
   TcRnAbstractClosedTyFamDecl :: TcRnMessage
 
-  {-| TcRnPartialFieldSelector is a warning indicating that a record selector
+  {-| TcRnPartialFieldSelector is a warning indicating that a record field
     was not defined for all constructors of a data type.
 
     Test cases:


=====================================
docs/users_guide/using-warnings.rst
=====================================
@@ -2154,7 +2154,7 @@ of ``-W(no-)*``.
 
     The option :ghc-flag:`-Wpartial-fields` warns about a record field
     ``f`` that is defined in some, but not all, of the constructors of a
-    data type, as such selector functions are partial. For example, when
+    data type, as record selection and update will be partial. For example, when
     :ghc-flag:`-Wpartial-fields` is enabled the compiler will emit a warning at
     the definition of ``Foo`` below: ::
 
@@ -2164,8 +2164,9 @@ of ``-W(no-)*``.
 
         data Foo = Foo { _f :: Int } | Bar
 
-    Another related warning is :ghc-flag:`-Wincomplete-record-selectors`,
-    which warns at use sites rather than definition sites.
+    Related warnings are :ghc-flag:`-Wincomplete-record-selectors` and
+    :ghc-flag:`-Wincomplete-record-updates`,
+    which warn at use sites rather than definition sites.
 
 .. ghc-flag:: -Wunused-packages
     :shortdesc: warn when package is requested on command line, but not needed.


=====================================
testsuite/tests/overloadedrecflds/should_fail/DRFPartialFields.stderr
=====================================
@@ -1,3 +1,4 @@
 
 DRFPartialFields.hs:4:17: error: [GHC-82712] [-Wpartial-fields, Werror=partial-fields]
-    Use of partial record field selector: ‘foo’
+    Definition of partial record field: ‘foo’
+    Record selection and update using this field will be partial.


=====================================
testsuite/tests/typecheck/should_compile/T7169.stderr
=====================================
@@ -1,2 +1,3 @@
 T7169.hs:11:5: warning: [GHC-82712] [-Wpartial-fields]
-    Use of partial record field selector: ‘m2’
+    Definition of partial record field: ‘m2’
+    Record selection and update using this field will be partial.



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/6c469bd2f5632ca59b691d07956ee61c717efbc0

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