Add support for pnpm workspaces as single derivation

Allow a caller to specify a workspace and a list of components rather
than a single source directory. This allows for the building of pnpm
monorepo projects with dependency links between the various projects and
a single pnpm-lock.yaml for the whole workspace. Requires that the
script has the same name in all components.

The location of all of the per-component package.json files is
overridable. A workspace project can still specify the location of the
root package.json via packageJSON, as well as the components'
package.json files via componentPackageJSONs. The list defaults to
c/package.json for c in components.

Similarly, the list of distDirs for the components is overridable. For a
workspace, the distDirs are all subdirs of $out rather than dist
becoming $out. The default list is c/dist for c in components. Allowing
for override handles the case where one component is built by a
different tool like next and produces a different directory like ".next"

NB: Any "link:" dependencies will need to be recreated as a preBuild
step. pnpm will create the symlinks during install, and nix removes them
because when the node_modules derivation is built, they are dangling.

Attempts to leave the non-workspace pnpm package support intact.

derivation.nix

@@ -1,6 +1,7 @@
 { lib
 , stdenv
 , nodejs
+, rsync
 , pkg-config
 , callPackage
 , writeText
@@ -15,15 +16,23 @@ let
 in
 {
   mkPnpmPackage =
-    { src
+    { workspace ? null
+    , components ? []
+    , src ? if (workspace != null && components != []) then workspace else null
     , packageJSON ? src + "/package.json"
+    , componentPackageJSONs ? map (c: {
+        name = "${c}/package.json";
+        value = src + "/${c}/package.json";
+      }) components
     , pnpmLockYaml ? src + "/pnpm-lock.yaml"
+    , pnpmWorkspaceYaml ? (if workspace == null then null else workspace + "/pnpm-workspace.yaml")
     , pname ? (fromJSON (readFile packageJSON)).name
     , version ? (fromJSON (readFile packageJSON)).version or null
     , name ? if version != null then "${pname}-${version}" else pname
     , registry ? "https://registry.npmjs.org"
     , script ? "build"
     , distDir ? "dist"
+    , distDirs ? (if workspace == null then [distDir] else (map (c: "${c}/dist") components))
     , installInPlace ? false
     , installEnv ? { }
     , buildEnv ? { }
@@ -38,17 +47,65 @@ in
     , ...
     }@attrs:
     let
+      # Flag that can be computed from arguments, indicating a workspace was
+      # supplied. Only used in these let bindings.
+      isWorkspace = workspace != null && components != [];
+      # Utility functions
+      forEachConcat = f: xs: concatStringsSep "\n" (map f xs);
+      forEachComponent = f: forEachConcat f components;
+      # Computed values used below that don't loop
       nativeBuildInputs = [
         nodejs
         pnpm
         pkg-config
-      ] ++ extraBuildInputs;
+      ] ++ extraBuildInputs ++ (optional copyNodeModules rsync);
+      copyLink =
+        if copyNodeModules
+          then "rsync -a --chmod=u+w"
+          else "ln -s";
+      rsyncSlash = optionalString copyNodeModules "/";
+      packageFilesWithoutLockfile =
+        [
+          { name = "package.json"; value = packageJSON; }
+        ] ++ componentPackageJSONs ++ computedNodeModuleSources;
+      computedNodeModuleSources =
+        (if pnpmWorkspaceYaml == null
+          then []
+          else [
+            {name = "pnpm-workspace.yaml"; value = pnpmWorkspaceYaml;}
+          ]
+        ) ++ extraNodeModuleSources;
+      # Computed values that loop over something
+      nodeModulesDirs =
+        if isWorkspace then
+          ["node_modules"] ++ (map (c: "${c}/node_modules") components)
+        else ["node_modules"];
+      filterString = concatStringsSep " " (
+        ["--recursive" "--stream"] ++
+        map (c: "--filter ./${c}") components
+      ) + " ";
+      buildScripts = ''
+        pnpm run ${optionalString isWorkspace filterString}${script}
+      '';
+      # Flag derived from value computed above, indicating the single dist
+      # should be copied as $out directly, rather than $out/${distDir}
+      computedDistDirIsOut =
+        length distDirs == 1 && !isWorkspace;
     in
     stdenv.mkDerivation (
       recursiveUpdate
         (rec {
           inherit src name nativeBuildInputs;
 
+          postUnpack = ''
+            ${optionalString (pnpmWorkspaceYaml != null) ''
+              cp ${pnpmWorkspaceYaml} pnpm-workspace.yaml
+            ''}
+            ${forEachComponent (component:
+              ''mkdir -p "${component}"'')
+            }
+          '';
+
           configurePhase = ''
             export HOME=$NIX_BUILD_TOP # Some packages need a writable HOME
             export npm_config_nodedir=${nodejs}
@@ -57,12 +114,11 @@ in
 
             ${if installInPlace
               then passthru.nodeModules.buildPhase
-              else ''
-                ${if !copyNodeModules
-                  then "ln -s"
-                  else "cp -r"
-                } ${passthru.nodeModules}/node_modules node_modules
-              ''
+              else
+                forEachConcat (
+                  nodeModulesDir: ''
+                    ${copyLink} ${passthru.nodeModules}/${nodeModulesDir}${rsyncSlash} ${nodeModulesDir}
+                  '') nodeModulesDirs
             }
 
             runHook postConfigure
@@ -77,15 +133,25 @@ in
 
             runHook preBuild
 
-            pnpm run ${script}
+            ${buildScripts}
 
             runHook postBuild
           '';
 
           installPhase = ''
             runHook preInstall
 
-            ${if distDir == "." then "cp -r" else "mv"} ${distDir} $out
+            ${if computedDistDirIsOut then ''
+                ${if distDir == "." then "cp -r" else "mv"} ${distDir} $out
+              ''
+              else ''
+                mkdir -p $out
+                ${forEachConcat (dDir: ''
+                    cp -r --parents ${dDir} $out
+                  '') distDirs
+                }
+              ''
+            }
 
             runHook postInstall
           '';
@@ -119,18 +185,19 @@ in
                 inherit nativeBuildInputs;
 
                 unpackPhase = concatStringsSep "\n"
-                  (
+                  ( [ # components is an empty list for non workspace builds
+                      (forEachComponent (component: ''
+                      mkdir -p "${component}"
+                    '')) ] ++
                     map
                       (v:
                         let
                           nv = if isAttrs v then v else { name = "."; value = v; };
                         in
-                        "cp -vr ${nv.value} ${nv.name}"
+                        "cp -vr \"${nv.value}\" \"${nv.name}\""
                       )
-                      ([
-                        { name = "package.json"; value = packageJSON; }
-                        { name = "pnpm-lock.yaml"; value = passthru.patchedLockfileYaml; }
-                      ] ++ extraNodeModuleSources)
+                      ([{ name = "pnpm-lock.yaml"; value = passthru.patchedLockfileYaml; }]
+                      ++ packageFilesWithoutLockfile)
                   );
 
                 buildPhase = ''
@@ -147,20 +214,24 @@ in
                     else "cp -RL"
                   } ${passthru.pnpmStore} $(pnpm store path)
 
-                  ${lib.optionalString copyPnpmStore "chmod -R +w $(pnpm store path)"}
+                  ${optionalString copyPnpmStore "chmod -R +w $(pnpm store path)"}
 
                   ${concatStringsSep "\n" (
                     mapAttrsToList
                       (n: v: ''export ${n}="${v}"'')
                       installEnv
                   )}
 
-                  pnpm install ${optionalString noDevDependencies "--prod "}--frozen-lockfile --offline
+                  pnpm install --stream ${optionalString noDevDependencies "--prod "}--frozen-lockfile --offline
                 '';
 
                 installPhase = ''
                   mkdir -p $out
                   cp -r node_modules/. $out/node_modules
+                  ${forEachComponent (component: ''
+                    mkdir -p $out/"${component}"
+                    cp -r "${component}/node_modules" $out/"${component}/node_modules"
+                  '')}
                 '';
               };
             };