Hadrian: Fix untracked dependencies

This is a preparation for #16295: https://ghc.haskell.org/trac/ghc/ticket/16295

This commit mostly focuses on getting rid of untracked dependencies,
which prevent Shake's new `--shared` feature from appropriately caching
build rules.

There are three different solutions to untracked dependencies:

* Track them! This is the obvious and the best approach, but in some
  situations we cannot use it, for example, because a build rule creates
  files whose names are not known statically and hence cannot be
  specified as the rule's outputs.

* Use Shake's `produces` to record outputs dynamically, within the rule.

* Use Shake's `historyDisable` to disable caching for a particular build
  rule. We currently use this approach only for `ghc-pkg` which mutates
  the package database and the file `package.cache`.

These two tickets are fixed as the result:

Ticket #16271: ​https://ghc.haskell.org/trac/ghc/ticket/16271

Ticket #16272: ​https://ghc.haskell.org/trac/ghc/ticket/16272 (this one
is fixed only partially: we correctly record the dependency, but we
still copy files into the RTS build tree).

1 files changed, 26 insertions, 7 deletions

diff --git a/hadrian/src/Packages.hs b/hadrian/src/Packages.hs
index 02dc134387..8d2aef1c7b 100644
--- a/hadrian/src/Packages.hs
+++ b/hadrian/src/Packages.hs
@@ -12,7 +12,8 @@ module Packages (
 
     -- * Package information
     programName, nonHsMainPackage, autogenPath, programPath, timeoutPath,
-    rtsContext, rtsBuildPath, libffiContext, libffiBuildPath, libffiLibraryName
+    rtsContext, rtsBuildPath, libffiContext, libffiBuildPath, libffiLibraryName,
+    generatedGhcDependencies, ensureConfigured
     ) where
 
 import Hadrian.Package
@@ -145,7 +146,7 @@ programName Context {..} = do
                                         (Profiling, "-prof"),
                                         (Dynamic,   "-dyn")
                                     ]]
-                              _               -> pkgName package
+                              _ -> pkgName package
 
 -- | The 'FilePath' to a program executable in a given 'Context'.
 programPath :: Context -> Action FilePath
@@ -170,8 +171,8 @@ timeoutPath = "testsuite/timeout/install-inplace/bin/timeout" <.> exe
 nonHsMainPackage :: Package -> Bool
 nonHsMainPackage = (`elem` [ghc, hp2ps, iserv, touchy, unlit])
 
--- TODO: Can we extract this information from Cabal files?
--- | Path to the @autogen@ directory generated when configuring a package.
+-- TODO: Combine this with 'programName'.
+-- | Path to the @autogen@ directory generated by 'buildAutogenFiles'.
 autogenPath :: Context -> Action FilePath
 autogenPath context@Context {..}
     | isLibrary package = autogen "build"
@@ -181,6 +182,16 @@ autogenPath context@Context {..}
   where
     autogen dir = contextPath context <&> (-/- dir -/- "autogen")
 
+-- | Make sure a given context has already been fully configured. The
+-- implementation simply calls 'need' on the context's @autogen/cabal_macros.h@
+-- file, which triggers 'configurePackage' and 'buildAutogenFiles'. Why this
+-- indirection? Going via @autogen/cabal_macros.h@ allows us to cache the
+-- configuration steps, i.e. not to repeat them if they have already been done.
+ensureConfigured :: Context -> Action ()
+ensureConfigured context = do
+    autogen <- autogenPath context
+    need [autogen -/- "cabal_macros.h"]
+
 -- | RTS is considered a Stage1 package. This determines RTS build directory.
 rtsContext :: Stage -> Context
 rtsContext stage = vanillaContext stage rts
@@ -189,9 +200,8 @@ rtsContext stage = vanillaContext stage rts
 rtsBuildPath :: Stage -> Action FilePath
 rtsBuildPath stage = buildPath (rtsContext stage)
 
--- | Build directory for libffi
--- This probably doesn't need to be stage dependent but it is for
--- consistency for now.
+-- | Build directory for @libffi@. This probably doesn't need to be stage
+-- dependent but it is for consistency for now.
 libffiContext :: Stage -> Context
 libffiContext stage = vanillaContext stage libffi
 
@@ -208,3 +218,12 @@ libffiLibraryName = do
         (True , False) -> "ffi"
         (False, False) -> "Cffi"
         (_    , True ) -> "Cffi-6"
+
+-- | Generated header files required by GHC in runtime.
+generatedGhcDependencies :: Stage -> Action [FilePath]
+generatedGhcDependencies stage = do
+    let context = vanillaContext stage compiler
+    bh <- buildPath   context <&> (-/- "ghc_boot_platform.h")
+    ch <- contextPath context <&> (-/- "ghc_boot_platform.h")
+    is <- includesDependencies
+    return $ is ++ [bh, ch]