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configureRequiredProgram: take care if program already configured
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‎Cabal/src/Distribution/Simple/Configure.hs‎

Lines changed: 70 additions & 48 deletions
Original file line numberDiff line numberDiff line change
@@ -2210,55 +2210,77 @@ configureRequiredProgram
22102210
verbosity
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progdb
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(LegacyExeDependency progName verRange) =
2213-
case lookupKnownProgram progName progdb of
2214-
Nothing ->
2215-
-- Try to configure it as a 'simpleProgram' automatically
2216-
--
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-- There's a bit of a story behind this line. In old versions
2218-
-- of Cabal, there were only internal build-tools dependencies. So the
2219-
-- behavior in this case was:
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--
2221-
-- - If a build-tool dependency was internal, don't do
2222-
-- any checking.
2223-
--
2224-
-- - If it was external, call 'configureRequiredProgram' to
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-- "configure" the executable. In particular, if
2226-
-- the program was not "known" (present in 'ProgramDb'),
2227-
-- then we would just error. This was fine, because
2228-
-- the only way a program could be executed from 'ProgramDb'
2229-
-- is if some library code from Cabal actually called it,
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-- and the pre-existing Cabal code only calls known
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-- programs from 'defaultProgramDb', and so if it
2232-
-- is calling something else, you have a Custom setup
2233-
-- script, and in that case you are expected to register
2234-
-- the program you want to call in the ProgramDb.
2235-
--
2236-
-- OK, so that was fine, until I (ezyang, in 2016) refactored
2237-
-- Cabal to support per-component builds. In this case, what
2238-
-- was previously an internal build-tool dependency now became
2239-
-- an external one, and now previously "internal" dependencies
2240-
-- are now external. But these are permitted to exist even
2241-
-- when they are not previously configured (something that
2242-
-- can only occur by a Custom script.)
2213+
case lookupProgramByName progName progdb of
2214+
Just prog ->
2215+
-- If the program has already been configured, use it
2216+
-- (as long as the version is compatible).
22432217
--
2244-
-- So, I decided, "Fine, let's just accept these in any
2245-
-- case." Thus this line. The alternative would have been to
2246-
-- somehow detect when a build-tools dependency was "internal" (by
2247-
-- looking at the unflattened package description) but this
2248-
-- would also be incompatible with future work to support
2249-
-- external executable dependencies: we definitely cannot
2250-
-- assume they will be preinitialized in the 'ProgramDb'.
2251-
configureProgram verbosity (simpleProgram progName) progdb
2252-
Just prog
2253-
-- requireProgramVersion always requires the program have a version
2254-
-- but if the user says "build-depends: foo" ie no version constraint
2255-
-- then we should not fail if we cannot discover the program version.
2256-
| verRange == anyVersion -> do
2257-
(_, progdb') <- requireProgram verbosity prog progdb
2258-
return progdb'
2259-
| otherwise -> do
2260-
(_, _, progdb') <- requireProgramVersion verbosity prog verRange progdb
2261-
return progdb'
2218+
-- Not doing so means falling back to the "simpleProgram" path below,
2219+
-- which might fail if the program has custom logic to find a version
2220+
-- (such as hsc2hs).
2221+
let loc = locationPath $ programLocation prog
2222+
in case programVersion prog of
2223+
Nothing
2224+
| verRange == anyVersion ->
2225+
return progdb
2226+
| otherwise ->
2227+
dieWithException verbosity $!
2228+
UnknownVersionDb (programId prog) verRange loc
2229+
Just version
2230+
| withinRange version verRange ->
2231+
return progdb
2232+
| otherwise ->
2233+
dieWithException verbosity $!
2234+
BadVersionDb (programId prog) version verRange loc
2235+
Nothing ->
2236+
-- Otherwise, try to configure it as a 'simpleProgram' automatically
2237+
case lookupKnownProgram progName progdb of
2238+
Nothing ->
2239+
-- There's a bit of a story behind this line. In old versions
2240+
-- of Cabal, there were only internal build-tools dependencies. So the
2241+
-- behavior in this case was:
2242+
--
2243+
-- - If a build-tool dependency was internal, don't do
2244+
-- any checking.
2245+
--
2246+
-- - If it was external, call 'configureRequiredProgram' to
2247+
-- "configure" the executable. In particular, if
2248+
-- the program was not "known" (present in 'ProgramDb'),
2249+
-- then we would just error. This was fine, because
2250+
-- the only way a program could be executed from 'ProgramDb'
2251+
-- is if some library code from Cabal actually called it,
2252+
-- and the pre-existing Cabal code only calls known
2253+
-- programs from 'defaultProgramDb', and so if it
2254+
-- is calling something else, you have a Custom setup
2255+
-- script, and in that case you are expected to register
2256+
-- the program you want to call in the ProgramDb.
2257+
--
2258+
-- OK, so that was fine, until I (ezyang, in 2016) refactored
2259+
-- Cabal to support per-component builds. In this case, what
2260+
-- was previously an internal build-tool dependency now became
2261+
-- an external one, and now previously "internal" dependencies
2262+
-- are now external. But these are permitted to exist even
2263+
-- when they are not previously configured (something that
2264+
-- can only occur by a Custom script.)
2265+
--
2266+
-- So, I decided, "Fine, let's just accept these in any
2267+
-- case." Thus this line. The alternative would have been to
2268+
-- somehow detect when a build-tools dependency was "internal" (by
2269+
-- looking at the unflattened package description) but this
2270+
-- would also be incompatible with future work to support
2271+
-- external executable dependencies: we definitely cannot
2272+
-- assume they will be preinitialized in the 'ProgramDb'.
2273+
configureProgram verbosity (simpleProgram progName) progdb
2274+
Just prog
2275+
-- requireProgramVersion always requires the program have a version
2276+
-- but if the user says "build-depends: foo" ie no version constraint
2277+
-- then we should not fail if we cannot discover the program version.
2278+
| verRange == anyVersion -> do
2279+
(_, progdb') <- requireProgram verbosity prog progdb
2280+
return progdb'
2281+
| otherwise -> do
2282+
(_, _, progdb') <- requireProgramVersion verbosity prog verRange progdb
2283+
return progdb'
22622284

22632285
-- -----------------------------------------------------------------------------
22642286
-- Configuring pkg-config package dependencies

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