Fix executable output of buildIdris nix helper (#3188)

CHANGELOG_NEXT.md

@@ -14,6 +14,13 @@ This CHANGELOG describes the merged but unreleased changes. Please see [CHANGELO
   installed with sourcecode files or not; other than that, `library`
   functionally replaces `installLibrary`.
 
+* The Nix flake's `buildIdris` `executable` property (previously `build`) has
+  been fixed in a few ways. It used to output a non-executable file for NodeJS
+  builds (now the file has the executable bit set). It used to output the
+  default Idris2 wrapper for Scheme builds which relies on utilities not
+  guaranteed at runtime by the Nix derivation; now it rewraps the output to only
+  depend on the directory containing Idris2's runtime support library.
+
 * The Nix flake now exposes the Idris2 API package as `idris2-api` and Idris2's
   C support library as `support`.
 

flake.nix

@@ -47,6 +47,7 @@
           buildIdris = pkgs.callPackage ./nix/buildIdris.nix {
             inherit idris2-version;
             idris2 = idris2Pkg;
+            support = idris2Support;
           };
           idris2ApiPkg = buildIdris {
             src = ./.;

nix/buildIdris.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, idris2-version, idris2 }:
+{ stdenv, lib, idris2-version, idris2, support, makeWrapper }:
 { src, projectName, idrisLibraries, ... }@attrs:
 
 let
@@ -12,7 +12,8 @@ in rec {
   executable = stdenv.mkDerivation (drvAttrs // {
     name = projectName;
     src = src;
-    nativeBuildInputs = [ idris2 ];
+    buildInputs = idrisLibraries ++ attrs.buildInputs or [];
+    nativeBuildInputs = [ idris2 makeWrapper ] ++ attrs.nativeBuildInputs or [];
     configurePhase = ''
       runHook preConfigure
       export IDRIS2_PACKAGE_PATH=${lib-dirs}
@@ -26,7 +27,20 @@ in rec {
     installPhase = ''
       runHook preInstall
       mkdir -p $out/bin
-      mv build/exec/* $out/bin
+      scheme_app="$(find ./build/exec -name '*_app')"
+      if [ "$scheme_app" = ''' ]; then
+        mv -- build/exec/* $out/bin/
+        chmod +x $out/bin/*
+      else
+        cd build/exec/*_app
+        for file in *.so; do
+          bin_name="''${file%.so}"
+          mv -- "$file" "$out/bin/$bin_name"
+          wrapProgram "$out/bin/$bin_name" \
+            --prefix LD_LIBRARY_PATH : ${lib.makeLibraryPath [ support ]} \
+            --prefix DYLD_LIBRARY_PATH : ${lib.makeLibraryPath [ support ]}
+        done
+      fi
       runHook postInstall
     '';
   });