nix-shell: also add a wrapper script besides the alias

... as aliases are not honored in `nix-shell --run`. In this way,
we can add an outer script running all the tests in the correct
environment.

4 files changed, 19 insertions, 2 deletions

diff --git a/README.md b/README.md
index 5ab1a0d..1ae6676 100644
--- a/README.md
+++ b/README.md
@@ -73,7 +73,8 @@ way as follows.
    pinned using [niv](https://github.com/nmattia/niv).
  - A [nix shell](./shell.nix) uses the derivation at the pinned
    snapshot of the `nixpkgs` and sets an alias for `just-mr` to
-   use the derived rc-file.
+   use the derived rc-file. It also adds a script `withRc-just-mr`
+   that execs `just-mr` with the derived rc-file.
 
 So to build with the correct dependencies for the checked out version,
 simply start a `nix-shell` at the top level of this repository and
@@ -90,6 +91,11 @@ by using the current justbuild when checking out older snapshots,
 we can reconstruct the old actions without the need of cleaning up
 the local build root.
 
+The just described way of working in a `nix-shell` using the
+alias is useful for interactive development. For CI-like usage,
+the script [run-tests](./run-tests) can be used that simply runs
+`withRc-just-mr` in a `nix-shell`.
+
 ## Shell commands
 
 The built-in rule `"generic"` allows to define a target by
diff --git a/nix-dependencies/dependencies.nix b/nix-dependencies/dependencies.nix
index 10a1b3e..2e73468 100644
--- a/nix-dependencies/dependencies.nix
+++ b/nix-dependencies/dependencies.nix
@@ -1,5 +1,6 @@
 { stdenv
 , jo
+, bash
 , pkg-config
 , coreutils
 , protobuf_25
@@ -25,6 +26,7 @@ stdenv.mkDerivation rec {
     protobuf_25
     grpc
     jo
+    bash
   ];
 
   buildInputs = [
@@ -52,12 +54,19 @@ stdenv.mkDerivation rec {
           ) > config.json
     cat config.json
     jo "just files"=$(jo config=$(jo -a $(jo root=system path=$out/share/config.json))) > rc.json
+
+    cat > withRc-just-mr <<EOF
+    #!${bash}/bin/bash
+    exec just-mr --rc $out/share/rc.json "\$@"
+    EOF
   '';
 
   installPhase = ''
-    mkdir -p $out/share
+    mkdir -p $out/share $out/bin
     cp config.json $out/share
     cp rc.json $out/share
+    cp withRc-just-mr $out/bin
+    chmod 555 $out/bin/withRc-just-mr
   '';
 
 }
diff --git a/run-tests b/run-tests
new file mode 100755
index 0000000..c3d4938
--- /dev/null
+++ b/run-tests
@@ -0,0 +1 @@
+nix-shell --run "withRc-just-mr --main test build"
diff --git a/shell.nix b/shell.nix
index a42d2ae..70c8edd 100644
--- a/shell.nix
+++ b/shell.nix
@@ -17,6 +17,7 @@ in pkgs.mkShell rec {
      niv
      update-deps
      cargo
+     nix-dependencies
   ];
 
   shellHook = ''