Initializing record with similarly named field from a different record results in warning rather than error

When a record is initialized using a similarly named field from another record, the compiler ignores the initialization and generates a warning instead of throwing an error. I believe this is a bug introduced in GHC 8.0.1 (and probably related to DuplicateRecordFields), since earlier versions of GHC would refuse to compile the code.

Consider the following example:

-- A.hs
module A where
  data A = A { a :: (), b :: () }

-- B.hs
module B where
  data B = B { a :: (), b :: () }

-- Main.hs
module Main where
  import A hiding (a)
  import B

  x = A { a = (), b = () }

  main = case x of
    A () () -> return ()

On GHC 8.0.1, this compiles (with a warning), and the program throws an exception when run:

$ stack ghc --compiler ghc-8.0.1 -- --make Main.hs
[1 of 3] Compiling B                ( B.hs, B.o )
[2 of 3] Compiling A                ( A.hs, A.o )
[3 of 3] Compiling Main             ( Main.hs, Main.o )

Main.hs:5:7: warning: [-Wmissing-fields]
    • Fields of ‘A’ not initialised: a
    • In the expression: A {a = (), b = ()}
      In an equation for ‘x’: x = A {a = (), b = ()}
Linking Main ...

$ ./Main 
Main: Main.hs:5:7-26: Missing field in record construction a

On GHC 7.10.3, the program will not compile:

$ stack ghc --compiler ghc-7.10.3 -- --make Main.hs
[1 of 3] Compiling B                ( B.hs, B.o )
[2 of 3] Compiling A                ( A.hs, A.o )
[3 of 3] Compiling Main             ( Main.hs, Main.o )

Main.hs:5:7:
    Constructor ‘A’ does not have field ‘a’
    In the expression: A {a = (), b = ()}
    In an equation for ‘x’: x = A {a = (), b = ()}

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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