command-not-found: drop perl dependency

Faster startup and remove some perl packages from the default nixos closure.
Eventually we could remove perl completely from the default nixos closure.

nixos/modules/programs/command-not-found/command-not-found.nix

@@ -9,20 +9,8 @@ with lib;
 
 let
   cfg = config.programs.command-not-found;
-  commandNotFound = pkgs.substituteAll {
-    name = "command-not-found";
-    dir = "bin";
-    src = ./command-not-found.pl;
-    isExecutable = true;
-    inherit (pkgs) perl;
-    inherit (cfg) dbPath;
-    perlFlags = concatStrings (map (path: "-I ${path}/${pkgs.perl.libPrefix} ")
-      [ pkgs.perlPackages.DBI pkgs.perlPackages.DBDSQLite pkgs.perlPackages.StringShellQuote ]);
-  };
-
-in
-
-{
+  commandNotFound = pkgs.callPackage ./. { dbPath = cfg.dbPath; };
+in {
   options.programs.command-not-found = {
 
     enable = mkOption {

nixos/modules/programs/command-not-found/default.nix

@@ -0,0 +1,19 @@
+{ stdenv, sqlite, pkgconfig,
+  dbPath ? "/nix/var/nix/profiles/per-user/root/channels/nixos/programs.sqlite"
+}:
+# build with: nix-build -E '(import <nixpkgs> {}).callPackage ./. {}'
+stdenv.mkDerivation {
+  name = "command-not-found";
+  src = ./src;
+  buildInputs = [ sqlite ];
+  nativeBuildInputs = [ pkgconfig ];
+  installPhase = ''
+    mkdir -p $out/bin
+    $CXX -O2 -std=c++17 -Wall \
+      -DDB_PATH=\"${dbPath}\" \
+      -DNIX_SYSTEM=\"${stdenv.system}\" \
+      $(pkg-config --cflags --libs sqlite3) \
+      -o $out/bin/command-not-found \
+      command-not-found.cpp
+  '';
+}

nixos/modules/programs/command-not-found/src/command-not-found.cpp

@@ -0,0 +1,79 @@
+#include <memory>
+#include <stdio.h>
+#include <functional>
+#include <string>
+#include <vector>
+
+#include <sqlite3.h>
+
+int queryPackages(std::string system, std::string program,
+                  std::vector<std::string> &packages) {
+  sqlite3 *raw_db = nullptr;
+  if (sqlite3_open(DB_PATH, &raw_db) != SQLITE_OK) {
+    fprintf(stderr, "cannot open database \"%s\": %s\n", DB_PATH,
+            sqlite3_errmsg(raw_db));
+  };
+  std::unique_ptr<sqlite3, std::function<void(sqlite3*)>> db(raw_db, [](auto db) { sqlite3_close(db); });
+
+  const char *sql =
+      "select package from Programs where system = ? and name = ?;";
+
+  sqlite3_stmt *raw_stmt = nullptr;
+  if (sqlite3_prepare_v2(db.get(), sql, -1, &raw_stmt, NULL) != SQLITE_OK) {
+    fprintf(stderr, "Failed to prepare query: %s\n", sqlite3_errmsg(db.get()));
+    return 1;
+  }
+  std::unique_ptr<sqlite3_stmt, std::function<void(sqlite3_stmt*)>> stmt(raw_stmt, [](auto stmt) { sqlite3_finalize(stmt); });
+
+  if (sqlite3_bind_text(stmt.get(), 1, system.c_str(), -1, 0) != SQLITE_OK) {
+    fprintf(stderr, "Failed to bind system parameter: %s\n",
+            sqlite3_errmsg(db.get()));
+    return 1;
+  };
+  if (sqlite3_bind_text(stmt.get(), 2, program.c_str(), -1, 0) != SQLITE_OK) {
+    fprintf(stderr, "Failed to bind program parameter: %s\n",
+            sqlite3_errmsg(db.get()));
+    return 1;
+  };
+
+  while (sqlite3_step(stmt.get()) == SQLITE_ROW) {
+    packages.push_back((const char *)(sqlite3_column_text(stmt.get(), 0)));
+  }
+
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  const char *system = getenv("NIX_SYSTEM");
+  const char *program = argv[1];
+
+  if (!system) {
+    system = NIX_SYSTEM;
+  }
+
+  if (argc < 2) {
+    fprintf(stderr, "USAGE: %s PROGRAM\n", argv[0]);
+    return 1;
+  }
+
+  std::vector<std::string> packages = {};
+  if (queryPackages(system, program, packages) < 0) {
+    return 1;
+  };
+
+  if (packages.size()) {
+    auto advice = packages.size() > 1 ?
+      "It is provided by several packages. You can install it by typing on of the of following commands:\n" :
+      "You can install it by typing:";
+    fprintf(stderr,
+            "The program '%s' is currently not installed. %s\n",
+            program, advice);
+    for (auto pkg : packages) {
+      fprintf(stderr, "  nix-env -iA nixos.%s\n", pkg.c_str());
+    }
+  } else {
+    fprintf(stderr, "%s: command not found\n", program);
+  }
+
+  return 127;
+}