Add collectChecks functions (input-output-hk#498)

Fixes input-output-hk#482.

Author: michaelpj

docs/reference/library.md

@@ -281,7 +281,7 @@ Assorted functions for operating on [Haskell.nix][] data. This is
 distinct from `pkgs.haskell.lib` in the current Nixpkgs Haskell
 Infrastructure.
 
-### collectComponents and collectComponents'
+### collectComponents, collectComponents'
 
 Extracts a selection of components from a Haskell [package set](#package-set).
 
@@ -316,6 +316,12 @@ tests = collectComponents "tests" (package: package.identifier.name == "mypackag
 Will result in moving derivations from `hsPkgs.mypackage.components.tests.unit-tests`
 to `tests.mypackage.unit-tests`.
 
+### collectChecks, collectChecks'
+
+These are just like `collectComponents` and `collectComponents'`, except that they collect
+the `checks` attributes of packages (which aren't components, and so can't be collected
+by the other functions.
+
 #### check
 
 This function turns a derivation that builds a test into one to run it.

lib/default.nix

@@ -161,6 +161,17 @@ with haskellLib;
   #    myTests = collectComponents' "tests" myHaskellPackages;
   collectComponents' = group: collectComponents group (_: true);
 
+  # Extracts a selection of 'checks' from a Haskell package set.
+  #
+  # This can be used to collect all the test runs in your project, so that can be run in CI.
+  collectChecks = packageSel: haskellPackages:
+    let packageFilter = name: package: (package.isHaskell or false) && packageSel package;
+    in recurseIntoAttrs (lib.mapAttrs (_: p: p.checks) (lib.filterAttrs packageFilter haskellPackages));
+
+  # Equivalent to collectChecks with (_: true) as selection function.
+  # Useful for pre-filtered package-set.
+  collectChecks' = collectChecks (_: true);
+
   # Replacement for lib.cleanSourceWith that has a subDir argument.
   inherit (import ./clean-source-with.nix { inherit lib; }) cleanSourceWith canCleanSource;