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Simon Peyton Jones pushed to branch wip/spj-reinstallable-base at Glasgow Haskell Compiler / GHC

Commits:

93148501
by Simon Peyton Jones at 2026-03-20T20:23:49+00:00
```
Wibbles, mainly comments
```

5 changed files:

compiler/GHC/Iface/Binary.hs
compiler/GHC/Iface/Env.hs
compiler/GHC/Rename/Env.hs
compiler/GHC/Rename/Names.hs
compiler/GHC/Types/Name.hs

Changes:

@@ -654,13 +654,17 @@ initNameWriterTable = do
  putSymbolTable :: WriteBinHandle -> Int -> UniqFM Name (Int,Name) -> IO ()
 -putSymbolTable bh name_count symtab = do
 -    put_ bh name_count
 -    let names = elems (array (0,name_count-1) (nonDetEltsUFM symtab))
 -      -- It's OK to use nonDetEltsUFM here because the elements have
 -      -- indices that array uses to create order
 -    mapM_ (\n -> serialiseName bh n symtab) names
+-
 +putSymbolTable bh name_count symtab
 +  = do { put_ bh name_count
 +       ; let names = elems (array (0,name_count-1) (nonDetEltsUFM symtab))
 +             -- It's OK to use nonDetEltsUFM here because the elements
 +             -- have indices that array uses to create order
 +       ; mapM_ serialise_one names }
 +  where
 +    serialise_one :: Name -> IO ()
 +    serialise_one name
 +      | (mod, occ, is_known_key) <- extNamePieces name
 +      = put_ bh (moduleUnit mod, moduleName mod, occ, is_known_key)
  getSymbolTable :: ReadBinHandle -> NameCache -> IO (SymbolTable Name)
  -- Create an array of Names for the symbols and add them to the NameCache
@@ -697,11 +701,6 @@ getSymbolTable bh name_cache
                  ; writeArray mut_arr (fromIntegral i) name
                  ; return new_cache }
 -serialiseName :: WriteBinHandle -> Name -> UniqFM key (Int,Name) -> IO ()
 -serialiseName bh name _
 -  | (mod, occ, is_known_key) <- extNamePieces name
 -  = put_ bh (moduleUnit mod, moduleName mod, occ, is_known_key)
+-
  -- Note [Symbol table representation of names]
  -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  --

compiler/GHC/Iface/Env.hs

@@ -92,7 +92,7 @@ allocateGlobalBinder
    -> Module -> OccName -> Maybe Unique -> SrcSpan
    -> IO Name
  -- See Note [The Name Cache] in GHC.Types.Name.Cache
 -allocateGlobalBinder nc mod occ mb_uniq loc
 +oallocateGlobalBinder nc mod occ mb_uniq loc
    = updateNameCache nc mod occ $ \cache0 -> do
        case lookupOrigNameCache cache0 mod occ of
          -- A hit in the cache!  We are at the binding site of the name.

compiler/GHC/Rename/Env.hs

@@ -250,6 +250,7 @@ newTopVanillaSrcBinder occ loc
    = do { this_mod <- getModule
         -- See if this bindings is for a known-key name, and if so get its Unique
 +       -- See 'Defining known-key names' in GHC.Types.Name
         ; defines_known_keys <- goptM Opt_DefinesKnownKeyNames
         ; let mb_uniq :: Maybe Unique
               mb_uniq | defines_known_keys = lookupOccEnv knownKeyOccMap occ

compiler/GHC/Rename/Names.hs

@@ -2025,7 +2025,8 @@ findImportUsage rebindable_known_key_names imports used_gres
            = acc
            -- -frebindable-known-key-names is on, and `n` is a known-key name
 -          -- Then don't warn about an unused imports.
 +          -- Then don't warn about an unused import.
 +          -- See (UI2) in Note [Unused imports]
            | rebindable_known_key_names
            , isKnownKeyName n
            = acc
@@ -2253,31 +2254,6 @@ warnUnusedImport rdr_env (L loc decl, used, unused, unused_wcs)
        [ UnusedImportWildcard wc | wc <- unused_wcs ] ++
        [ possible_field nm | nm <- sortBy (comparing nameOccName) unused ]
 -{-
 -Note [Do not warn about Prelude hiding]
 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 -We do not warn about
 -   import Prelude hiding( x, y )
 -because even if nothing else from Prelude is used, it may be essential to hide
 -x,y to avoid name-shadowing warnings.  Example (#9061)
 -   import Prelude hiding( log )
 -   f x = log where log = ()
+-
+-
+-
 -Note [Printing minimal imports]
 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 -To print the minimal imports we walk over all import decls (both user-supplied
 -and generated), trim their import lists, then filter out generated decls.
+-
 -NB that
+-
 -  * We do *not* change the 'qualified' or 'as' parts!
+-
 -  * We do not discard a decl altogether; we might need instances
 -    from it.  Instead we just trim to an empty import list
 --}
+-
  getMinimalImports :: [ImportDeclUsage] -> RnM [LImportDecl GhcRn]
  getMinimalImports ie_decls
    = do { rdr_env <- getGlobalRdrEnv
@@ -2399,7 +2375,51 @@ to_ie_post_rn (L l n)
    | otherwise                   = L l (IEName noExtField (L (l2l l) n))
    where occ = occName n
 -{-
 +{- Note [Do not warn about Prelude hiding]
 +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 +We do not warn about
 +   import Prelude hiding( x, y )
 +because even if nothing else from Prelude is used, it may be essential to hide
 +x,y to avoid name-shadowing warnings.  Example (#9061)
 +   import Prelude hiding( log )
 +   f x = log where log = ()
++
 +Note [Unused imports]
 +~~~~~~~~~~~~~~~~~~~~~
 +In `warnUnusedImport`, if we see an import with an explicit list imports, thus
 +   import M( a, b )
 +and neither `a` nor `b` is used, we report the entire import decl as unused.  We
 +check this by looking at the names that it brings into scope scope; if there are
 +no ununused names, don't report.
++
 +This neatly takes into account two things:
++
 +(UI1) We don't want to complain about `import M()`, because that is often used to bring
 +   M's /instances/ into scope.
++
 +(UI2) In base:Data.Enum we see
 +            import GHC.Internal.Num( Num ) -- For -frebindable-known-key-names (defaulting)
 +   'Num' is not mentioned explicity but the import is still required; see KKNS_InScope
 +   in Note [Overview of known-key names] in GHC.Types.Name.
++
 +   We don't want this import reported at an unused. So `findImportUsage`, when looking
 +   at `import M( x )`,  we do /not/ record `x` as "unused" (regardless of whether it is
 +   mentioned in M if
 +        (a) -frebindable-known-key-names is on, and
 +        (b) `x` is a known-key name
++
 +Note [Printing minimal imports]
 +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 +To print the minimal imports we walk over all import decls (both user-supplied
 +and generated), trim their import lists, then filter out generated decls.
++
 +NB that
++
 +  * We do *not* change the 'qualified' or 'as' parts!
++
 +  * We do not discard a decl altogether; we might need instances
 +    from it.  Instead we just trim to an empty import list
++
  Note [Partial export]
  ~~~~~~~~~~~~~~~~~~~~~
  Suppose we have

compiler/GHC/Types/Name.hs

@@ -190,6 +190,11 @@ To implement all this, here are the moving parts:
    This is one reason for (KnownKeyInvariant): an export list cannot have two
    entities with the same OccName.
 +* There are two flags that control the treatment of known-key names:
 +    -frebindable-known-key-names
 +    -fdefines-known-key-names
 +  Details in the following bullets.
++
  * Known-key name lookup (normal case: KKNS_FromModule)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In normal client code, suppose the desugarer calls `dsLookupKnownKeyTyCon`
@@ -218,18 +223,27 @@ To implement all this, here are the moving parts:
    to bring into scope some entities that are needed by `dsLookupKnownKeyTyCon` etc.
    See also wrinkle (KKN1)
 -* Defin
 -* There are two flags that control the treatment of known-key names:
 -    -frebindable-known-key-names
 -    -fdefines-known-key-names
+-
 -* Suppose the desugarer calls `dsLookupKnownKeyTyCon` on `rationalTyConKey`.
 -  * In client source code, that is, /without/ -frebindable-known-key-names,
 -    we try to import GHC.KnownKeyNames.  Assuming this is succesful,
 +* Defining known-key names
 +  ~~~~~~~~~~~~~~~~~~~~~~~~
 +  When we /define/ a known-key name, such as
 +      the `Num` class in ghc-internal:GHC.Internal.Num
 +  we must assign the correct Unique. So in GHC.Rename.Env.newTopVanillaSrcBinder
 +  if -fdefines-known-key-names is set (Opt_DefinesKnownKeyNames), we check the
 +  OccName against the list in `basicKnownKeyTable`; if it appears there, we use the
 +  Unique from the table.
++
 +* Serialising known-key names
 +  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 +  - When we serialise a known-key name into an interface file, we mark it as such.
 +    See `serialise_one` in GHC.Iface.Binary.putSymbolTable.
 +  - When deserialising a name from an interface file, we check the known-key bit,
 +    If it is set, we get the Unique from the `basicKnownKeyTable`,
 +    and use `mkKnownKeyName` rather than `mkExternalName` to build the Name.
  Wrinkles
 -(KKN1) In
 +(KKN1) We need some special treatment of unused-import warnings.
 +   See (UI1) in Note [Unused imports] in GHC.Rename.Names
  Note [About the NameSorts]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~