#16331: REGRESSION: --supported-languages lies about supported languages, again -------------------------------------+------------------------------------- Reporter: hvr | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- To make it short, recent version of GHC broke the very thing we fixed in #11102 for GHC 8.0. This is utterly frustrating to me. ;-( Basically, if GHC advertises an extension, it's supposed to work without jumping through hoops if you enable it via `{-# LANGUAGE ... #-}` or `-X`-flags. Otherwise this breaks the whole idea of `other-extensions` and related cabal spec features which use `--supported-languages` to infer whether e.g. GHC when invoked with `-XTemplateHaskell` will succeed. However, consider the `Main.hs` below {{{#!hs {-# LANGUAGE TemplateHaskell #-} main = $undefined }}} Unfortuantely now GHC lies unconditionally about supporting TH, thereby undermining the infrastructure we setup in and for #11102: {{{ $ ghc --supported-languages | grep ^TemplateHaskell$ TemplateHaskell $ ghc --make Foo.hs [1 of 1] Compiling Main ( Foo.hs, Foo.o ) ghc-stage2: this operation requires -fexternal-interpreter }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16331 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler