pnpm.fetchDeps: Add workspaces support and support for custom pnpm configuration commands

Solves #316908

doc/languages-frameworks/javascript.section.md

@@ -346,11 +346,11 @@ NOTE: It is highly recommended to use a pinned version of pnpm (i.e. `pnpm_8` or
 
 In case you are patching `package.json` or `pnpm-lock.yaml`, make sure to pass `finalAttrs.patches` to the function as well (i.e. `inherit (finalAttrs) patches`.
 
+`pnpm.configHook` supports adding additional `pnpm install` flags via `pnpmInstallFlags` which can be set to a Nix string array.
+
 #### Dealing with `sourceRoot` {#javascript-pnpm-sourceRoot}
 
-NOTE: Nixpkgs pnpm tooling doesn't support building projects with a `pnpm-workspace.yaml`, or building monorepos. It maybe possible to use `pnpm.fetchDeps` for these projects, but it may be hard or impossible to produce a binary from such projects ([an example attempt](https://github.com/NixOS/nixpkgs/pull/290715#issuecomment-2144543728)).
-
-If the pnpm project is in a subdirectory, you can just define `sourceRoot` or `setSourceRoot` for `fetchDeps`. Note, that projects using `pnpm-workspace.yaml` are currently not supported, and will probably not work using this approach.
+If the pnpm project is in a subdirectory, you can just define `sourceRoot` or `setSourceRoot` for `fetchDeps`.
 If `sourceRoot` is different between the parent derivation and `fetchDeps`, you will have to set `pnpmRoot` to effectively be the same location as it is in `fetchDeps`.
 
 Assuming the following directory structure, we can define `sourceRoot` and `pnpmRoot` as follows:
@@ -375,6 +375,55 @@ Assuming the following directory structure, we can define `sourceRoot` and `pnpm
   pnpmRoot = "frontend";
 ```
 
+#### PNPM Workspaces {#javascript-pnpm-workspaces}
+
+If you need to use a PNPM workspace for your project, then set `pnpmWorkspace = "<workspace project name>"` in your `pnpm.fetchDeps` call,
+which will make PNPM only install dependencies for that workspace package.
+
+For example:
+
+```nix
+...
+pnpmWorkspace = "@astrojs/language-server";
+pnpmDeps = pnpm.fetchDeps {
+  inherit (finalAttrs) pnpmWorkspace;
+  ...
+}
+```
+
+The above would make `pnpm.fetchDeps` call only install dependencies for the `@astrojs/language-server` workspace package.
+Note that you do not need to set `sourceRoot` to make this work.
+
+Usually in such cases, you'd want to use `pnpm --filter=$pnpmWorkspace build` to build your project, as `npmHooks.npmBuildHook` probably won't work. A `buildPhase` based on the following example will probably fit most workspace projects:
+
+```nix
+buildPhase = ''
+  runHook preBuild
+
+  pnpm --filter=@astrojs/language-server build
+
+  runHook postBuild
+'';
+```
+
+#### Additional PNPM Commands and settings {#javascript-pnpm-extraCommands}
+
+If you require setting an additional PNPM configuration setting (such as `dedupe-peer-dependents` or similar),
+set `prePnpmInstall` to the right commands to run. For example:
+
+```nix
+prePnpmInstall = ''
+  pnpm config set dedupe-peer-dependants false
+'';
+pnpmDeps = pnpm.fetchDeps {
+  inherit (finalAttrs) prePnpmInstall;
+  ...
+};
+```
+
+In this example, `prePnpmInstall` will be run by both `pnpm.configHook` and by the `pnpm.fetchDeps` builder.
+
+
 ### Yarn {#javascript-yarn}
 
 Yarn based projects use a `yarn.lock` file instead of a `package-lock.json` to pin dependencies. Nixpkgs provides the Nix function `fetchYarnDeps` which fetches an offline cache suitable for running `yarn install` before building the project. In addition, Nixpkgs provides the hooks:

pkgs/development/tools/pnpm/fetch-deps/default.nix

@@ -14,6 +14,8 @@
     {
       hash ? "",
       pname,
+      pnpmWorkspace ? "",
+      prePnpmInstall ? "",
       ...
     }@args:
     let
@@ -29,6 +31,7 @@
             outputHash = "";
             outputHashAlgo = "sha256";
           };
+      installFlags = lib.optionalString (pnpmWorkspace != "")  "--filter=${pnpmWorkspace}";
     in
     stdenvNoCC.mkDerivation (finalAttrs: (
       args'
@@ -58,11 +61,14 @@
           pnpm config set side-effects-cache false
           # As we pin pnpm versions, we don't really care about updates
           pnpm config set update-notifier false
+          # Run any additional pnpm configuration commands that users provide.
+          ${prePnpmInstall}
           # pnpm is going to warn us about using --force
           # --force allows us to fetch all dependencies including ones that aren't meant for our host platform
           pnpm install \
               --force \
               --ignore-scripts \
+              ${installFlags} \
               --frozen-lockfile
 
           runHook postInstall

pkgs/development/tools/pnpm/fetch-deps/pnpm-config-hook.sh

@@ -24,9 +24,15 @@ pnpmConfigHook() {
 
     echo "Installing dependencies"
 
+    if [[ -n "$pnpmWorkspace" ]]; then
+        pnpmInstallFlags+=("--filter=$pnpmWorkspace")
+    fi
+    runHook prePnpmInstall
+
     pnpm install \
         --offline \
         --ignore-scripts \
+        "${pnpmInstallFlags[@]}" \
         --frozen-lockfile