hadrian: Produce ar archives with L modifier on Windows

Since object files may in fact be archive files, we must ensure that
their contents are merged rather than constructing an
archive-of-an-archive.

See #21068.

5 files changed, 41 insertions, 1 deletions

diff --git a/configure.ac b/configure.ac
index 71879adeb0..95d0043f59 100644
--- a/configure.ac
+++ b/configure.ac
@@ -848,6 +848,7 @@ AC_PROG_INSTALL
 
 dnl ** how to invoke `ar' and `ranlib'
 FP_PROG_AR_SUPPORTS_ATFILE
+FP_PROG_AR_SUPPORTS_DASH_L
 FP_PROG_AR_NEEDS_RANLIB
 
 dnl ** Check to see whether ln -s works
diff --git a/hadrian/cfg/system.config.in b/hadrian/cfg/system.config.in
index 0c2a76b7ac..6544261cd3 100644
--- a/hadrian/cfg/system.config.in
+++ b/hadrian/cfg/system.config.in
@@ -40,6 +40,7 @@ python         = @PythonCmd@
 #============================
 
 ar-supports-at-file = @ArSupportsAtFile@
+ar-supports-dash-l  = @ArSupportsDashL@
 cc-llvm-backend     = @CcLlvmBackend@
 hs-cpp-args         = @HaskellCPPArgs@
 
diff --git a/hadrian/src/Oracles/Flag.hs b/hadrian/src/Oracles/Flag.hs
index 7da72546e3..40ae3e8f9b 100644
--- a/hadrian/src/Oracles/Flag.hs
+++ b/hadrian/src/Oracles/Flag.hs
@@ -12,6 +12,7 @@ import Base
 import Oracles.Setting
 
 data Flag = ArSupportsAtFile
+          | ArSupportsDashL
           | CrossCompiling
           | CcLlvmBackend
           | GhcUnregisterised
@@ -34,6 +35,7 @@ flag :: Flag -> Action Bool
 flag f = do
     let key = case f of
             ArSupportsAtFile     -> "ar-supports-at-file"
+            ArSupportsDashL      -> "ar-supports-dash-l"
             CrossCompiling       -> "cross-compiling"
             CcLlvmBackend        -> "cc-llvm-backend"
             GhcUnregisterised    -> "ghc-unregisterised"
diff --git a/hadrian/src/Settings/Builders/Ar.hs b/hadrian/src/Settings/Builders/Ar.hs
index a4b08d6358..08379f07f8 100644
--- a/hadrian/src/Settings/Builders/Ar.hs
+++ b/hadrian/src/Settings/Builders/Ar.hs
@@ -8,7 +8,13 @@ import Settings.Builders.Common
 arBuilderArgs :: Args
 arBuilderArgs = mconcat
     [ builder (Ar Pack) ? mconcat
-      [ arg "q"
+      [ -- When building on platforms which don't support object merging
+        -- we must use the -L flag supported by llvm-ar, which ensures that
+        -- .a files added to the archive are merged into the resulting archive,
+        -- not added as a single file. This requires that we are using llvm-ar
+        --
+        -- See Note [Object merging] in GHC.Driver.Pipeline.Execute for details.
+        ifM ((&&) <$> notStage0 <*> expr (flag ArSupportsDashL)) (arg "qL") (arg "q")
       , arg =<< getOutput
       ]
     , builder (Ar Unpack) ? mconcat
diff --git a/m4/fp_prog_ar_supports_dash_l.m4 b/m4/fp_prog_ar_supports_dash_l.m4
new file mode 100644
index 0000000000..3ec26db548
--- /dev/null
+++ b/m4/fp_prog_ar_supports_dash_l.m4
@@ -0,0 +1,30 @@
+# FP_PROG_AR_SUPPORTS_DASH_L
+# -----------------
+# Sets fp_prog_ar_supports_dash_l to yes or no, depending on whether
+# or not it supports the llvm-ar's -L flag to merge archives.
+AC_DEFUN([FP_PROG_AR_SUPPORTS_DASH_L],
+[
+  AC_REQUIRE([FP_PROG_AR])
+  AC_REQUIRE([FP_PROG_AR_ARGS])
+  AC_CACHE_CHECK([whether $fp_prog_ar supports -L], [fp_cv_prog_ar_supports_dash_l],
+    [
+      rm -f conftest*
+      touch conftest.file
+      touch conftest.a0 conftest.a1 conftest.b0 conftest.b1
+      dnl Build two archives, merge them, and check that the result contains the
+      dnl original files not the two archives.
+      "$fp_prog_ar" qc conftest-a.a conftest.a0 conftest.a1
+      "$fp_prog_ar" qc conftest-b.a conftest.b0 conftest.b1
+      "$fp_prog_ar" qcL conftest.a conftest-a.a conftest-b.a 2>/dev/null
+      if "$fp_prog_ar" t conftest.a | grep -s "conftest.a1" > /dev/null
+      then
+        fp_cv_prog_ar_supports_dash_l=yes
+      else
+        fp_cv_prog_ar_supports_dash_l=no
+      fi
+      rm -f conftest*
+    ])
+  fp_prog_ar_supports_dash_l=$fp_cv_prog_ar_supports_dash_l
+  AC_SUBST([ArSupportsDashL], [`echo $fp_prog_ar_supports_dash_l | tr 'a-z' 'A-Z'`])
+])# FP_PROG_AR_SUPPORTS_DASH_L
+