Hadrian: Add support for building stage3

This ticket enables the building of a `stage3` compiler by making the
build logic more consistent and predictable in Hadrian.

Two of the main changes are:

1. In order to build anything at stageN we use the package database
present at stageN. Fixing #16069
2. `haddock` and `ghc-tags` are built
as stage1 executables (with the stage1 compiler) rather than as
stage2 compiler. Fixing
[hadrian#661](https://github.com/snowleopard/hadrian/issues/661)

In order to build a stage3 compiler, you have to set the new `finalStage` hadrian option to `Stage3`.

4 files changed, 12 insertions, 12 deletions

diff --git a/hadrian/src/Settings/Builders/Common.hs b/hadrian/src/Settings/Builders/Common.hs
index 6846c4bc8d..cfe0911292 100644
--- a/hadrian/src/Settings/Builders/Common.hs
+++ b/hadrian/src/Settings/Builders/Common.hs
@@ -61,9 +61,8 @@ packageDatabaseArgs = do
     stage <- getStage
     dbPath <- expr (packageDbPath stage)
     expr (need [dbPath -/- packageDbStamp])
-    root <- getBuildRoot
     prefix <- ifM (builder Ghc) (return "-package-db ") (return "--package-db=")
-    arg $ prefix ++ root -/- relativePackageDbPath stage
+    arg $ prefix ++ dbPath
 
 bootPackageDatabaseArgs :: Args
 bootPackageDatabaseArgs = do
diff --git a/hadrian/src/Settings/Builders/Configure.hs b/hadrian/src/Settings/Builders/Configure.hs
index 068591dfbb..214aed6c27 100644
--- a/hadrian/src/Settings/Builders/Configure.hs
+++ b/hadrian/src/Settings/Builders/Configure.hs
@@ -7,7 +7,8 @@ import Settings.Builders.Common
 configureBuilderArgs :: Args
 configureBuilderArgs = do
     gmpPath    <- expr gmpBuildPath
-    libffiPath <- expr libffiBuildPath
+    stage      <- getStage
+    libffiPath <- expr (libffiBuildPath stage)
     mconcat [ builder (Configure gmpPath) ? do
                 hostPlatform  <- getSetting HostPlatform
                 buildPlatform <- getSetting BuildPlatform
diff --git a/hadrian/src/Settings/Builders/Make.hs b/hadrian/src/Settings/Builders/Make.hs
index 102ba54845..0433888279 100644
--- a/hadrian/src/Settings/Builders/Make.hs
+++ b/hadrian/src/Settings/Builders/Make.hs
@@ -10,11 +10,12 @@ makeBuilderArgs :: Args
 makeBuilderArgs = do
     threads    <- shakeThreads <$> expr getShakeOptions
     gmpPath    <- expr gmpBuildPath
-    libffiPath <- expr libffiBuildPath
+    libffiPaths <- forM [Stage1 ..] $ \s -> expr (libffiBuildPath s)
     let t = show $ max 4 (threads - 2) -- Don't use all Shake's threads
-    mconcat
-        [ builder (Make gmpPath   ) ? pure ["MAKEFLAGS=-j" ++ t]
-        , builder (Make libffiPath) ? pure ["MAKEFLAGS=-j" ++ t, "install"] ]
+    mconcat $
+        (builder (Make gmpPath   ) ? pure ["MAKEFLAGS=-j" ++ t]) :
+        [ builder (Make libffiPath) ? pure ["MAKEFLAGS=-j" ++ t, "install"]
+        | libffiPath <- libffiPaths ]
 
 validateBuilderArgs :: Args
 validateBuilderArgs = builder (Make "testsuite/tests") ? do
diff --git a/hadrian/src/Settings/Default.hs b/hadrian/src/Settings/Default.hs
index b0e269ce1b..2cadc4fc79 100644
--- a/hadrian/src/Settings/Default.hs
+++ b/hadrian/src/Settings/Default.hs
@@ -108,7 +108,9 @@ stage1Packages = do
              , stm
              , time
              , unlit
-             , xhtml                         ]
+             , xhtml
+             , ghcTags                       ]
+          ++ [ haddock | not cross           ]
           ++ [ hpcBin   | not cross          ]
           ++ [ iserv    | not win, not cross ]
           ++ [ libiserv | not win, not cross ]
@@ -119,10 +121,7 @@ stage1Packages = do
 
 -- | Packages built in 'Stage2' by default. You can change this in "UserSettings".
 stage2Packages :: Action [Package]
-stage2Packages = do
-    cross <- flag CrossCompiling
-    return $ [ ghcTags             ]
-          ++ [ haddock | not cross ]
+stage2Packages = stage1Packages
 
 -- | Packages that are built only for the testsuite.
 testsuitePackages :: Action [Package]