[Git][ghc/ghc][wip/spj-apporv-Oct24] look through applications to check if we need deepsubsumption

24 Nov 2025


      Apoorv Ingle pushed to branch wip/spj-apporv-Oct24 at Glasgow Haskell Compiler / GHC


Commits:
2003c4ab by Apoorv Ingle at 2025-11-24T10:04:35-06:00
look through applications to check if we need deepsubsumption

- - - - -


7 changed files:

- compiler/GHC/CmmToAsm.hs
- compiler/GHC/Iface/Ext/Ast.hs
- compiler/GHC/Tc/Gen/App.hs
- + testsuite/tests/typecheck/should_compile/ExpansionQLIm.hs
- testsuite/tests/typecheck/should_compile/all.T
- testsuite/tests/typecheck/should_fail/T7857.stderr
- testsuite/tests/typecheck/should_fail/tcfail181.stderr


Changes:

=====================================
compiler/GHC/CmmToAsm.hs
=====================================
@@ -1,4 +1,3 @@
-{-# LANGUAGE DeepSubsumption #-}
 -- -----------------------------------------------------------------------------
 --
 -- (c) The University of Glasgow 1993-2004


=====================================
compiler/GHC/Iface/Ext/Ast.hs
=====================================
@@ -1157,7 +1157,8 @@ the typechecker:
   * HsDo, where we give the SrcSpan of the entire do block to each
     ApplicativeStmt.
   * Expanded (via ExpandedThingRn) ExplicitList{}, where we give the SrcSpan of the original
-    list expression to the 'fromListN' call.
+    list expression to the expanded expression. The 'fromListN' is assigned
+    a generated location span
 
 In order for the implicit function calls to not be confused for actual
 occurrences of functions in the source code, most of this extra information


=====================================
compiler/GHC/Tc/Gen/App.hs
=====================================
@@ -486,11 +486,18 @@ getDeepSubsumptionFlag_DataConHead app_head =
      ; return $
          if | user_ds
             -> Deep DeepSub
-            | XExpr (ConLikeTc (RealDataCon {})) <- app_head
-            -> Deep TopSub
             | otherwise
-            -> Shallow
-    }
+            -> go app_head
+     }
+  where
+    go :: HsExpr GhcTc -> DeepSubsumptionFlag
+    go app_head
+     | XExpr (ConLikeTc (RealDataCon {})) <- app_head
+     = Deep TopSub
+     | HsApp _ f _ <- app_head
+     = go (unLoc f)
+     | otherwise
+     = Shallow
 
 finishApp :: (HsExpr GhcTc, SrcSpan) -> [HsExprArg 'TcpTc]
           -> TcRhoType -> HsWrapper


=====================================
testsuite/tests/typecheck/should_compile/ExpansionQLIm.hs
=====================================
@@ -0,0 +1,10 @@
+module Test where
+
+
+qqqq :: [String]
+qqqq = (show (1 :: Int) :) $ ["2"]
+
+main :: IO ()
+main = do
+  putStrLn "abc"
+  putStrLn $ concat qqqq


=====================================
testsuite/tests/typecheck/should_compile/all.T
=====================================
@@ -658,8 +658,8 @@ def onlyHsParLocs(x):
     """
     ls = x.split("\n")
     filteredLines = (loc.strip() for (loc,hspar) in zip(ls,ls[5:])
-                      if hspar.strip().startswith("(HsPar")
-                        and not "<no location info>" in loc)
+		      if hspar.strip().startswith("(HsPar")
+			and not "<no location info>" in loc)
     return '\n'.join(filteredLines)
 test('T15242', normalise_errmsg_fun(onlyHsParLocs), compile, [''])
 test('T15431', normal, compile, [''])
@@ -957,3 +957,4 @@ test('T17705', normal, compile, [''])
 test('T14745', normal, compile, [''])
 test('T26451', normal, compile, [''])
 test('T26582', normal, compile, [''])
+test('ExpansionQLIm', normal, compile, [''])


=====================================
testsuite/tests/typecheck/should_fail/T7857.stderr
=====================================
@@ -1,8 +1,7 @@
-
 T7857.hs:8:11: error: [GHC-39999]
     • Could not deduce ‘PrintfType a0’ arising from a use of ‘printf’
-      from the context: PrintfArg t
-        bound by the inferred type of g :: PrintfArg t => t -> b
+      from the context: PrintfArg q
+        bound by the inferred type of g :: PrintfArg q => q -> b
         at T7857.hs:8:1-21
       The type variable ‘a0’ is ambiguous
       Potentially matching instances:
@@ -15,3 +14,4 @@ T7857.hs:8:11: error: [GHC-39999]
     • In the second argument of ‘($)’, namely ‘printf "" i’
       In the expression: f $ printf "" i
       In an equation for ‘g’: g i = f $ printf "" i
+


=====================================
testsuite/tests/typecheck/should_fail/tcfail181.stderr
=====================================
@@ -1,5 +1,5 @@
 tcfail181.hs:17:9: error: [GHC-39999]
-    • Could not deduce ‘Monad m0’ arising from a record update
+    • Could not deduce ‘Monad m0’ arising from a use of ‘foo’
       from the context: Monad m
         bound by the inferred type of
                    wog :: Monad m => p -> Something (m Bool) e



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/2003c4abed79548f64a4bfb760960894...

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Apoorv Ingle (＠ani)

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