Add Backpack support.

builder/comp-builder.nix

@@ -145,6 +145,22 @@ let
 
   disableFeature = disable: enableFeature (!disable);
 
+  # This function uses nested sed commands to
+  # 1. Uses sed to build a regex line for (2) command by replacing 'inplace' with a regex.
+  # 2. Extracts the packageId from the configure-flags file using the regex from (1).
+  # 3. Replaces the 'inplace' substring with the extracted packageId in 'instLine' configuration line.
+  replaceInplaceWithAbiHash = instLine:
+    if lib.strings.hasInfix "inplace" instLine then
+      let
+        # We print the 'instLine' and replace the 'inplace' substring with a regex which we will use later
+        instLineWithRegex = "<(echo ${instLine} | sed -n -e 's/.*=\\(.*\\)-inplace-\\(.*\\):.*/\\1-\\\\\\\\([^\"]*\\\\\\\\)-\\2/p')";
+        # We execute 'instLineWithRegex' into 'sedline' variable and use it again to extract the packageId from 'configure-flags'
+        packageIdLine = "<(read sedline < ${instLineWithRegex}; sed -n -e \"s/.*\$\{sedline\}/\\1/p\" ${configFiles}/configure-flags | head -1)";
+      in
+        # We read the packageId from the previous sed command and replace the 'inplace' substring with 'packageId'
+        "$(read packageId < ${packageIdLine}; echo ${instLine} | sed -n -e \"s/\\(.*\\)-inplace-\\(.*\\)/\\1-\$\{packageId\}-\\2/p\")"
+    else instLine;
+
   finalConfigureFlags = lib.concatStringsSep " " (
     [ "--prefix=$out"
     ] ++
@@ -161,8 +177,21 @@ let
       if configureAllComponents
         then ["--enable-tests" "--enable-benchmarks"]
         else ["${haskellLib.componentTarget componentId}"]
-    ) ++ [ "$(cat ${configFiles}/configure-flags)"
-    ] ++ commonConfigureFlags);
+    ) ++ [
+      # We have to use sed here to patch 'configure-flags' file to drop the abi hash suffix.
+      #
+      # plan2nix created packages for sublibs with instantiated signatures and they have
+      # names like 'domain+EwFBnH3u8XWEhAhZr7XmS1' where 'domain' is the original sublib's name.
+      #
+      # To build them we pass the folllowing configure flags:
+      # '--dependency=<package-name>:<sublib-name>=<package-name>-<version>-<abi-hash>-domain+EwFBnH3u8XWEhAhZr7XmS1'
+      # which is incorrect and the build fails. The build of the instantiated sublib should be called just like for
+      # the original sublib:
+      # '--dependency=<package-name>:<sublib-name>=<package-name>-<version>-<abi-hash>-domain'
+      "$(sed 's/--dependency=\\(.*\\)+\\(.*\\)/--dependency=\\1/' ${configFiles}/configure-flags)"
+    ] ++ commonConfigureFlags ++
+    (map (arg: "--instantiate-with=" + replaceInplaceWithAbiHash arg) component.instantiatedWith)
+    );
 
   # From nixpkgs 20.09, the pkg-config exe has a prefix matching the ghc one
   pkgConfigHasPrefix = builtins.compareVersions lib.version "20.09pre" >= 0;

lib/default.nix

@@ -106,7 +106,9 @@ in {
 
   # Format a componentId as it should appear as a target on the
   # command line of the setup script.
-  componentTarget = componentId:"${componentId.ctype}:${componentId.cname}";
+  #
+  # We omit the suffix that starts with '+' because libraries with instantiated signatures are being built by their usual name.
+  componentTarget = componentId:"${componentId.ctype}:${builtins.head (builtins.split "\\+" componentId.cname)}";
 
   # Remove null or empty values from an attrset.
   optionalHooks = lib.filterAttrs (_: hook: hook != null && hook != "");

modules/configuration-nix.nix

@@ -53,6 +53,7 @@ in {
   packages.cabal-install.patches = [
     (fromUntil "3.4.0.0" "3.5" ../overlays/patches/Cabal/Cabal-3.4-defer-build-tool-depends-7532.patch)
     (fromUntil "3.4.0.0" "3.5" ../overlays/patches/Cabal/Cabal-3.4-speedup-solver-when-tests-enabled-7490.patch)
+    (fromUntil "3.6.0.0" "3.9.0.0" ../overlays/patches/Cabal/Cabal-3.6.0.0-instantiated-with.diff)
   ];
 
   # Avoid dependency on genprimopcode and deriveConstants (cabal does not put these in the plan,

modules/plan.nix

@@ -55,6 +55,10 @@ let
             type = bool;
             default = true;
          };
+         instantiatedWith = mkOption {
+            type = listOfFilteringNulls str;
+            default = (def.instantiatedWith or []);
+         };
          configureFlags = mkOption {
             type = listOfFilteringNulls str;
             default = (def.configureFlags or []);