Allow per-component builds with coverage enabled

This commits re-enables per-component builds when coverage checking is
enabled. This restriction was previously added in haskell#5004 to fix haskell#4798.

However, the fix for haskell#5213, in haskell#7493, fixes the paths of the testsuite
`.mix` files to the same location as that of the main library component,
which in turn fixes haskell#4798 as well -- meaning the restriction to treat
testsuites per-package (legacy-fallback) is no longer needed.

Lifting this restriction additionally fixes haskell#6440 as we no longer
constrain coverage to per-package builds only, thus allowing multi-libs.

To generate hpc files in the appropriate component directories in the
distribution tree, we move the hack from haskell#7493 from dictating the `.mix`
directories where hpc information is stored to dictating the `.mix`
directories that are included in the call to `hpc markup`.

Fixes haskell#6440, and the already previously fixed haskell#4798, haskell#5213.

Cabal/src/Distribution/Simple/Hpc.hs

@@ -76,31 +76,7 @@ mixDir
   -- ^ Component name
   -> FilePath
   -- ^ Directory containing test suite's .mix files
-mixDir distPref way name = hpcDir distPrefBuild way </> "mix" </> name
-  where
-    -- This is a hack for HPC over test suites, needed to match the directory
-    -- where HPC saves and reads .mix files when the main library of the same
-    -- package is being processed, perhaps in a previous cabal run (#5213).
-    -- E.g., @distPref@ may be
-    -- @./dist-newstyle/build/x86_64-linux/ghc-9.0.1/cabal-gh5213-0.1/t/tests@
-    -- but the path where library mix files reside has two less components
-    -- at the end (@t/tests@) and this reduced path needs to be passed to
-    -- both @hpc@ and @ghc@. For non-default optimization levels, the path
-    -- suffix is one element longer and the extra path element needs
-    -- to be preserved.
-    distPrefElements = splitDirectories distPref
-    distPrefBuild = case drop (length distPrefElements - 3) distPrefElements of
-      ["t", _, "noopt"] ->
-        joinPath $
-          take (length distPrefElements - 3) distPrefElements
-            ++ ["noopt"]
-      ["t", _, "opt"] ->
-        joinPath $
-          take (length distPrefElements - 3) distPrefElements
-            ++ ["opt"]
-      [_, "t", _] ->
-        joinPath $ take (length distPrefElements - 2) distPrefElements
-      _ -> distPref
+mixDir distPref way name = hpcDir distPref way </> "mix" </> name
 
 tixDir
   :: FilePath
@@ -146,14 +122,14 @@ markupTest
   :: Verbosity
   -> LocalBuildInfo
   -> FilePath
-  -- ^ \"dist/\" prefix
+  -- ^ Testsuite \"dist/\" prefix
   -> String
   -- ^ Library name
   -> TestSuite
   -> Library
   -> IO ()
-markupTest verbosity lbi distPref libraryName suite library = do
-  tixFileExists <- doesFileExist $ tixFilePath distPref way $ testName'
+markupTest verbosity lbi testDistPref libraryName suite library = do
+  tixFileExists <- doesFileExist $ tixFilePath testDistPref way $ testName'
   when tixFileExists $ do
     -- behaviour of 'markup' depends on version, so we need *a* version
     -- but no particular one
@@ -163,12 +139,12 @@ markupTest verbosity lbi distPref libraryName suite library = do
         hpcProgram
         anyVersion
         (withPrograms lbi)
-    let htmlDir_ = htmlDir distPref way testName'
+    let htmlDir_ = htmlDir testDistPref way testName'
     markup
       hpc
       hpcVer
       verbosity
-      (tixFilePath distPref way testName')
+      (tixFilePath testDistPref way testName')
       mixDirs
       htmlDir_
       (exposedModules library)
@@ -179,14 +155,16 @@ markupTest verbosity lbi distPref libraryName suite library = do
   where
     way = guessWay lbi
     testName' = unUnqualComponentName $ testName suite
-    mixDirs = map (mixDir distPref way) [testName', libraryName]
+    mixDirs = [ mixDir testDistPref way testName'
+              , mixDir (pathToMainLibHpc testDistPref) way libraryName
+              ]
 
 -- | Generate the HTML markup for all of a package's test suites.
 markupPackage
   :: Verbosity
   -> LocalBuildInfo
   -> FilePath
-  -- ^ \"dist/\" prefix
+  -- ^ Testsuite \"dist/\" prefix
   -> PD.PackageDescription
   -> [TestSuite]
   -> IO ()
@@ -215,6 +193,40 @@ markupPackage verbosity lbi distPref pkg_descr suites = do
   where
     way = guessWay lbi
     testNames = fmap (unUnqualComponentName . testName) suites
-    mixDirs = map (mixDir distPref way) $ libraryName : testNames
+    mixDirs = mixDir (pathToMainLibHpc distPref) way libraryName : map (mixDir distPref way) testNames
     included = concatMap (exposedModules) $ PD.allLibraries pkg_descr
     libraryName = prettyShow $ PD.package pkg_descr
+
+-- | A (non-exported) hack to determine the path to the main-lib hpc directory
+-- given the testsuite's dist prefix.
+--
+-- We use this function when constructing calls to `hpc markup` since otherwise
+-- having cabal-install communicate the path to the main lib dist-dir when
+-- building the test component, via the Setup.hs interface, is far more
+-- complicated.
+pathToMainLibHpc :: FilePath -> FilePath
+pathToMainLibHpc distPref = distPrefBuild
+  where
+    -- This is a hack for HPC over test suites, needed to match the directory
+    -- where HPC saves and reads .mix files when the main library of the same
+    -- package is being processed, perhaps in a previous cabal run (#5213).
+    -- E.g., @distPref@ may be
+    -- @./dist-newstyle/build/x86_64-linux/ghc-9.0.1/cabal-gh5213-0.1/t/tests@
+    -- but the path where library mix files reside has two less components
+    -- at the end (@t/tests@) and this reduced path needs to be passed to
+    -- both @hpc@ and @ghc@. For non-default optimization levels, the path
+    -- suffix is one element longer and the extra path element needs
+    -- to be preserved.
+    distPrefElements = splitDirectories distPref
+    distPrefBuild = case drop (length distPrefElements - 3) distPrefElements of
+      ["t", _, "noopt"] ->
+        joinPath $
+          take (length distPrefElements - 3) distPrefElements
+            ++ ["noopt"]
+      ["t", _, "opt"] ->
+        joinPath $
+          take (length distPrefElements - 3) distPrefElements
+            ++ ["opt"]
+      [_, "t", _] ->
+        joinPath $ take (length distPrefElements - 2) distPrefElements
+      _ -> distPref

cabal-install/src/Distribution/Client/ProjectPlanning.hs

@@ -1673,7 +1673,7 @@ elaborateInstallPlan
         where
           -- You are eligible to per-component build if this list is empty
           why_not_per_component g =
-            cuz_buildtype ++ cuz_spec ++ cuz_length ++ cuz_flag ++ cuz_coverage
+            cuz_buildtype ++ cuz_spec ++ cuz_length ++ cuz_flag
             where
               cuz reason = [text reason]
               -- We have to disable per-component for now with
@@ -1710,12 +1710,6 @@ elaborateInstallPlan
                 | fromFlagOrDefault True (projectConfigPerComponent sharedPackageConfig) =
                     []
                 | otherwise = cuz "you passed --disable-per-component"
-              -- Enabling program coverage introduces odd runtime dependencies
-              -- between components.
-              cuz_coverage
-                | fromFlagOrDefault False (packageConfigCoverage localPackagesConfig) =
-                    cuz "program coverage is enabled"
-                | otherwise = []
 
           -- \| Sometimes a package may make use of features which are only
           -- supported in per-package mode.  If this is the case, we should

cabal-testsuite/PackageTests/Regression/T4798/T4798.cabal

@@ -0,0 +1,18 @@
+cabal-version:       >=1.10
+name:                T4798
+version:             0.1
+
+library
+  exposed-modules:     U2F, U2F.Types
+  ghc-options: -Wall
+  build-depends:       base
+  hs-source-dirs:      src
+  default-language:    Haskell2010
+
+test-suite hspec-suite
+  type:       exitcode-stdio-1.0
+  main-is:    test.hs
+  ghc-options: -Wall
+  hs-source-dirs: tests
+  default-language:    Haskell2010
+  build-depends:  base, T4798

cabal-testsuite/PackageTests/Regression/T4798/cabal.project

@@ -0,0 +1 @@
+packages: .

cabal-testsuite/PackageTests/Regression/T4798/cabal.test.hs

@@ -0,0 +1,3 @@
+import Test.Cabal.Prelude
+main = cabalTest $ cabal "test" ["--enable-coverage"]
+

cabal-testsuite/PackageTests/Regression/T4798/src/U2F.hs

@@ -0,0 +1,6 @@
+module U2F where
+
+import U2F.Types
+
+ourCurve :: String
+ourCurve = "SEC_p256r1"

cabal-testsuite/PackageTests/Regression/T4798/src/U2F/Types.hs

@@ -0,0 +1,3 @@
+module UF2.Types where
+
+data U2FError = RegistrationParseError

cabal-testsuite/PackageTests/Regression/T4798/tests/test.hs

@@ -0,0 +1,6 @@
+import U2F
+import U2F.Types
+
+main = print ourCurve
+main :: IO ()
+