make sdists for other components available

It sometimes happens that we have API updates that don't violate
PVP (e.g. adding things). In those cases, we need the newer version
available and cabal-install's dependencies must be updated to
require it instead of the bootlib.

We stash these in an environment file, since that's the most
convenient way to get them into cabal-install's build environment.

Author: geekosaur

.github/workflows/check-sdist.yml

@@ -42,8 +42,10 @@ jobs:
 
       - uses: actions/checkout@v4
 
-      - name: Make sdist
-        run: cabal sdist cabal-install
+      - name: Make sdists
+        run: |
+          cabal sdist Cabal-syntax Cabal Cabal-hooks cabal-install-solver cabal-install
+          ls dist-newstyle/sdist
 
       - name: Install from sdist
         run: |
@@ -58,10 +60,21 @@ jobs:
           # dunno if this will ever be extended to freebsd, but grep -q is a gnu-ism
           if ghc-pkg --global --simple-output list Cabal | grep "^Cabal-$ver\\." >/dev/null; then
             # sigh, someone broke installing from tarballs
-            rm -rf cabal*.project Cabal Cabal-syntax cabal-install-solver cabal-install
+            rm -rf cabal*.project Cabal-syntax Cabal Cabal-hooks cabal-install-solver cabal-install
             tar xfz "$sdist"
-            cd "cabal-install-$cbl"*
-            cabal install
+            cd "cabal-install-"*
+            # note: we have all the sdists in a `package-env` because sometimes we need
+            # to allow newer versions of Cabal (for example, we're using something that
+            # was added to Cabal, which isn't a PVP violation as long as the old API is
+            # still there). This _shouldn't_ affect how the solver picks versions, so it
+            # should be safe.
+            here="$(pwd)"
+            for pkg in Cabal-syntax Cabal Cabal-hooks cabal-install-solver; do
+              # need ver suffix here so e.g. Cabal-* doesn't match Cabal-syntax-*
+              tar xfz "$here/dist-newstyle/sdist/$pkg-$ver"*".tar.gz"
+              (cd "$pkg-$ver"*; cabal install --lib --package-env="$here")
+            done
+            cabal install --package-env="$here"
           else
             echo No matching bootlib Cabal version to test against.
             exit 0