#14838: missing "incomplete-patterns" warning for TH-generated functions -------------------------------------+------------------------------------- Reporter: gelisam | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Amazing find. It turns out that this can all be tied back to this line of code (introduced in GHC 8.0, in commit 8a506104d5b5b71d5640afc69c992e0af40f2213): {{{#!hs ; unless (isGenerated origin) $ when (isAnyPmCheckEnabled dflags (DsMatchContext ctxt locn)) $ addTmCsDs (genCaseTmCs1 mb_scr new_vars) $ -- See Note [Type and Term Equality Propagation] checkMatches dflags (DsMatchContext ctxt locn) new_vars matches }}} Specifically, the `unless (isGenerated origin)` part. It turns out that `-Wincomplete-patterns` is completely suppressed for any code that has an `Origin` of `Generated`, and Template Haskell–spliced code happens to fall under that bucket. I see two ways out of this: 1. Go through the code in `Convert` and change every use of `Generated` to `FromSource`. 2. Come up with a separate origin for Template Haskell code (perhaps `FromTH`?). I'm not sure if it's worth the trouble, though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14838#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler