Enable overriding source-repository-packages from Nix.

This will be used for CI

default.nix

@@ -17,13 +17,15 @@
       stackage = sources.stackage-nix;
     };
   }
-, packages ? import ./nix { inherit system sources crossSystem config sourcesOverride haskellNix checkMaterialization enableHaskellProfiling; }
+, packages ? import ./nix { inherit system sources crossSystem config sourcesOverride haskellNix checkMaterialization enableHaskellProfiling git-source-repository-overrides; }
   # An explicit git rev to use, passed when we are in Hydra
   # Whether to check that the pinned shas for haskell.nix are correct. We want this to be
   # false, generally, since it does more work, but we set it to true in the CI
 , checkMaterialization ? false
   # Whether to build our Haskell packages (and their dependencies) with profiling enabled.
 , enableHaskellProfiling ? false
+, git-source-repository-overrides ? [ ]
+  # see pkgs/nix/haskell/haskell.nix for explanation
 }:
 let
   inherit (packages) pkgs marlowe sources;

nix/default.nix

@@ -7,6 +7,7 @@
 , haskellNix
 , checkMaterialization ? false
 , enableHaskellProfiling ? false
+, git-source-repository-overrides ? [ ]
 }:
 let
   ownOverlays =
@@ -39,7 +40,7 @@ let
     config = haskellNix.nixpkgsArgs.config // config;
   };
 
-  marlowe = import ./pkgs { inherit pkgs checkMaterialization enableHaskellProfiling sources; };
+  marlowe = import ./pkgs { inherit pkgs checkMaterialization enableHaskellProfiling sources git-source-repository-overrides; };
 
 in
 {

nix/pkgs/default.nix

@@ -4,6 +4,7 @@
 , config ? { allowUnfreePredicate = (import ../lib/unfree.nix).unfreePredicate; }
 , sources
 , enableHaskellProfiling
+, git-source-repository-overrides ? [ ]
 }:
 let
   inherit (pkgs) stdenv;
@@ -14,6 +15,7 @@ let
   haskell = pkgs.callPackage ./haskell {
     inherit gitignore-nix sources;
     inherit checkMaterialization enableHaskellProfiling;
+    inherit git-source-repository-overrides;
     inherit (sources) actus-tests;
 
     # This ensures that the utility scripts produced in here will run on the current system, not

nix/pkgs/haskell/default.nix

@@ -12,6 +12,7 @@
 , z3
 , enableHaskellProfiling
 , actus-tests
+, git-source-repository-overrides ? [ ]
 }:
 let
   # The Hackage index-state from cabal.project
@@ -42,6 +43,7 @@ let
       inherit enableHaskellProfiling;
       inherit deferPluginErrors;
       inherit actus-tests;
+      inherit git-source-repository-overrides;
     };
   project = baseProject { deferPluginErrors = false; };
   # The same as above, but this time with we defer plugin errors so that we

nix/pkgs/haskell/haskell.nix

@@ -15,6 +15,14 @@
   # it. If set to true, we will also build the haddocks for those packages.
 , deferPluginErrors
 , actus-tests
+, git-source-repository-overrides ? [ ]
+  # Override source-repository-package entries in cabal (useful for CI)
+  # List of attribute sets:
+  #  location
+  #  tag
+  #  sha256
+  #  subdir (optional list of strings)
+
 }:
 let
   r-packages = with rPackages; [ R tidyverse dplyr stringr MASS plotly shiny shinyjs purrr ];
@@ -35,7 +43,8 @@ let
     # At the moment, we only need one but conceivably we might need one for darwin in future.
     # See https://github.com/input-output-hk/nix-tools/issues/97
     materialized =
-      if pkgs.stdenv.hostPlatform.isLinux then ./materialized-linux
+      if git-source-repository-overrides != [ ] then null
+      else if pkgs.stdenv.hostPlatform.isLinux then ./materialized-linux
       else if pkgs.stdenv.hostPlatform.isDarwin then ./materialized-darwin
       else if pkgs.stdenv.hostPlatform.isWindows then ./materialized-windows
       else builtins.error "Don't have materialized files for this platform";
@@ -61,11 +70,22 @@ let
       "https://github.com/input-output-hk/plutus"."3f089ccf0ca746b399c99afe51e063b0640af547" = "1nx8xmdgwmnsla4qg4k67f5md8vm3p1p9i25ndalrqdg40z90486";
       "https://github.com/input-output-hk/plutus-apps"."404af7ac3e27ebcb218c05f79d9a70ca966407c9" = "00pv5ds99lf6lmws3a3ipsn9amg56ayc9b0wqki2gky464dm6gzr";
       "https://github.com/j-mueller/cardano-wallet"."6be73ab852c0592713dfe78218856d4a8a0ee69e" = "0rx5hvmbdv5dwb4qq39vyhisj0v75j21jbiivn3s3q9za6m6x1p4";
-    };
+    } // (builtins.listToAttrs (map (sro: { name = sro.location; value = { ${sro.tag} = sro.sha256; }; }) git-source-repository-overrides));
     # Configuration settings needed for cabal configure to work when cross compiling
     # for windows. We can't use `modules` for these as `modules` are only applied
     # after cabal has been configured.
-    cabalProjectLocal = lib.optionalString pkgs.stdenv.hostPlatform.isWindows ''
+    cabalProjectLocal = (builtins.concatStringsSep "\n" (map
+      (sro: ''
+        source-repository-package
+          type: git
+          location: ${sro.location}
+          tag: ${sro.tag}
+      '' + lib.optionalString (sro ? subdir) ''
+          subdir:
+            ${builtins.concatStringsSep "\n    " sro.subdir}
+        -- comment here for proper Nix string indentation
+      '')
+      git-source-repository-overrides)) + lib.optionalString pkgs.stdenv.hostPlatform.isWindows ''
       -- When cross compiling for windows we don't have a `ghc` package, so use
       -- the `plutus-ghc-stub` package instead.
       package plutus-tx-plugin