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585d7450

by Luite Stegeman at 2026-04-11T02:17:13-04:00

tc: discard warnings in tcUserStmt Plan C

We typecheck let_stmt twice, but we don't want the warnings twice!

see #26233

@@ -2367,8 +2367,9 @@ tcUserStmt (L loc (BodyStmt _ expr _ _))
                          -- The two-step process avoids getting two errors: one from
                          -- the expression itself, and one from the 'print it' part
                          -- This two-step story is very clunky, alas
 -                  , do { _ <- checkNoErrs (tcGhciStmts [let_stmt])
 +                  , do { _ <- checkNoErrs (discardWarnings (tcGhciStmts [let_stmt]))
                                  --- checkNoErrs defeats the error recovery of let-bindings
 +                                --- discardWarnings: warnings come from the second typecheck
                         ; tcGhciStmts [let_stmt, print_it] } ]
                -- Plans where we don't bind "it"

	1	+:set -Wall
	2	+truncate pi

 +<interactive>:2:1: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
 +    • Defaulting the type variable ‘a0’ to type ‘Double’ in the following constraints
 +        (RealFrac a0)
 +          arising from a use of ‘truncate’ at <interactive>:2:1-8
 +        (Floating a0) arising from a use of ‘pi’ at <interactive>:2:10-11
 +    • In the expression: truncate pi
 +      In an equation for ‘it’: it = truncate pi
++
 +<interactive>:2:1: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
 +    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraints
 +        (Show a0) arising from a use of ‘print’ at <interactive>:2:1-11
 +        (Integral a0) arising from a use of ‘it’ at <interactive>:2:1-11
 +    • In a stmt of an interactive GHCi command: print it
++

+3

@@ -391,3 +391,4 @@ test('GhciPackageRename',
       [extra_hc_opts("-hide-all-packages -package 'containers (Data.Map as Prelude)'")],
       ghci_script,
       ['GhciPackageRename.script'])
 +test('T26233', normal, ghci_script, ['T26233.script'])