Cabal- A framework for packaging Haskell software

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Note: Buildable versus requested versus enabled components

What's the difference between a buildable component (ala componentBuildable), a requested component (ala componentNameRequested), and an enabled component (ala componentEnabled)?

A component is buildable if, after resolving flags and conditionals, there is no buildable: False property in it. This is a static property that arises from the Cabal file and the package description flattening; once we have a PackageDescription buildability is known.

A component is requested if a user specified, via a the flags and arguments passed to configure, that it should be built. E.g., --enable-tests or --enable-benchmarks request all tests and benchmarks, if they are provided. What is requested can be read off directly from ComponentRequestedSpec. A requested component is not always buildable; e.g., a user may --enable-tests but one of the test suites may have buildable: False.

A component is enabled if it is BOTH buildable and requested. Once we have a LocalBuildInfo, whether or not a component is enabled is known.

Generally speaking, most Cabal API code cares if a component is enabled. (For example, if you want to run a preprocessor on each component prior to building them, you want to run this on each enabled component.)

Note that post-configuration, you will generally not see a non-buildable Component. This is because flattenPD will drop any such components from PackageDescription. See #3858 for an example where this causes problems.

data ComponentRequestedSpec Source #

Describes what components are enabled by user-interaction. See also this note in Distribution.Types.ComponentRequestedSpec.


Eq ComponentRequestedSpec Source # 
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Read ComponentRequestedSpec Source # 
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Show ComponentRequestedSpec Source # 
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Generic ComponentRequestedSpec Source # 
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Associated Types

type Rep ComponentRequestedSpec :: * -> * #

Binary ComponentRequestedSpec Source # 
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type Rep ComponentRequestedSpec Source # 
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type Rep ComponentRequestedSpec = D1 (MetaData "ComponentRequestedSpec" "Distribution.Types.ComponentRequestedSpec" "Cabal-" False) (C1 (MetaCons "ComponentRequestedSpec" PrefixI True) (S1 (MetaSel (Just "testsRequested") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Bool) :*: S1 (MetaSel (Just "benchmarksRequested") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Bool)) :+: C1 (MetaCons "OneComponentRequestedSpec" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 ComponentName)))

data ComponentDisabledReason Source #

A reason explaining why a component is disabled.


defaultComponentRequestedSpec :: ComponentRequestedSpec Source #

The default set of enabled components. Historically tests and benchmarks are NOT enabled by default.


componentNameRequested :: ComponentRequestedSpec -> ComponentName -> Bool Source #

Is this component name enabled? See also this note in Distribution.Types.ComponentRequestedSpec.


componentEnabled :: ComponentRequestedSpec -> Component -> Bool Source #

Is this component enabled? See also this note in Distribution.Types.ComponentRequestedSpec.


componentDisabledReason :: ComponentRequestedSpec -> Component -> Maybe ComponentDisabledReason Source #

Is this component disabled, and if so, why?