plugins/by-name: init

Add support for automatically importing any directories under
`plugins/by-name`.

Includes a validation test, which is run by CI and by the pre-commit hook.

tests/plugins-by-name.nix

@@ -0,0 +1,151 @@
+{
+  lib,
+  evaluatedNixvim,
+  linkFarmFromDrvs,
+  runCommandNoCCLocal,
+}:
+let
+  by-name = ../plugins/by-name;
+  options = lib.collect lib.isOption evaluatedNixvim.options;
+
+  # Option namespaces that we allow by-name plugins to declare
+  knownPluginNamespaces = [
+    "colorschemes"
+    "plugins"
+  ];
+
+  # Group by-name children by filetype; "regular", "directory", "symlink" and "unknown".
+  children =
+    let
+      apply =
+        prev: name: type:
+        prev // { ${type} = prev.${type} ++ [ name ]; };
+
+      nil = {
+        regular = [ ];
+        directory = [ ];
+        symlink = [ ];
+        unknown = [ ];
+      };
+    in
+    lib.foldlAttrs apply nil (builtins.readDir by-name);
+
+  # Find plugins by looking for `*.*.enable` options that are declared in `plugins/by-name`
+  by-name-enable-opts =
+    let
+      regex = ''/nix/store/[^/]+/plugins/by-name/(.*)'';
+      optionalPair =
+        opt: file:
+        let
+          result = builtins.match regex file;
+        in
+        lib.optional (result != null) {
+          # Use the file name relative to `plugins/by-name/`
+          name = builtins.head result;
+          # Use only the first two parts of the option location
+          value = lib.genList (builtins.elemAt opt.loc) 2;
+        };
+    in
+    lib.pipe options [
+      (builtins.filter (opt: builtins.length opt.loc == 3 && lib.last opt.loc == "enable"))
+      (builtins.concatMap (opt: (builtins.concatMap (optionalPair opt) opt.declarations)))
+      builtins.listToAttrs
+    ];
+in
+linkFarmFromDrvs "plugins-by-name" [
+  # Ensures all files matching `plugins/by-name/*` are directories
+  (runCommandNoCCLocal "file-types"
+    {
+      __structuredAttrs = true;
+      inherit (children) regular symlink unknown;
+    }
+    ''
+      declare -i errs=0
+
+      showErrs() {
+        type="$1"
+        shift
+
+        if (( $# > 0 )); then
+          ((++errs))
+          echo "Unexpected $type in plugins/by-name ($#):"
+          for f in "$@"; do
+            echo "  - $f"
+          done
+          echo
+        fi
+      }
+
+      showErrs 'symlinks' "''${symlink[@]}"
+      showErrs 'regular files' "''${regular[@]}"
+      showErrs 'unknown-type files' "''${unknown[@]}"
+
+      if (( $errs > 0 )); then
+        exit 1
+      fi
+      touch $out
+    ''
+  )
+
+  # Ensures all plugin enable options are declared in a directory matching the plugin name
+  (runCommandNoCCLocal "mismatched-plugin-names"
+    {
+      __structuredAttrs = true;
+
+      options = lib.pipe by-name-enable-opts [
+        (lib.filterAttrs (file: loc: file != lib.last loc))
+        (lib.mapAttrs (file: loc: lib.showOption loc))
+      ];
+
+      passthru = {
+        inherit evaluatedNixvim;
+      };
+    }
+    ''
+      if (( ''${#options[@]} > 0 )); then
+        echo "Found plugin modules with mismatched option & directory names (''${#options[@]})"
+        for file in "''${!options[@]}"; do
+          echo "- ''${options[$file]} is declared in '$file'"
+        done
+        exit 1
+      fi
+      touch $out
+    ''
+  )
+
+  # Ensure all plugin enable option are declared under an expected namespace
+  (runCommandNoCCLocal "unknown-plugin-namespaces"
+    {
+      __structuredAttrs = true;
+
+      # I'm sorry, I couldn't help implementing oxford-comma...
+      expected =
+        let
+          len = builtins.length knownPluginNamespaces;
+        in
+        lib.concatImapStringsSep ", " (
+          i: str: lib.optionalString (i > 1 && i == len) "or " + "`${str}`"
+        ) knownPluginNamespaces;
+
+      options = lib.pipe by-name-enable-opts [
+        (lib.filterAttrs (file: loc: !(builtins.elem (builtins.head loc) knownPluginNamespaces)))
+        (lib.mapAttrs (file: loc: "`${lib.showOption loc}`"))
+      ];
+
+      passthru = {
+        inherit evaluatedNixvim;
+      };
+    }
+    ''
+      if (( ''${#options[@]} > 0 )); then
+        echo "Found plugin modules with unknown option namespaces (''${#options[@]})"
+        echo "Expected all plugins to be scoped as $expected"
+        for file in "''${!options[@]}"; do
+          echo "- ''${options[$file]} is declared in '$file'"
+        done
+        exit 1
+      fi
+      touch $out
+    ''
+  )
+]