{ lib, stdenv, zig, src }:

stdenv.mkDerivation (finalAttrs: {
  pname = "srf-lsp";
  # Kept in step with build.zig.zon, which is also what the server reports in its
  # `initialize` response (see build.zig).
  version = "0.0.1";

  inherit src;

  __structuredAttrs = true;
  strictDeps = true;

  # Zig resolves build.zig.zon dependencies over the network, which the build
  # sandbox forbids. `fetchDeps` runs `zig build --fetch` inside a fixed-output
  # derivation, so the fetch happens once against a known hash and the real build
  # stays offline.
  #
  # This hash changes whenever build.zig.zon changes, which in practice means
  # whenever the srf dependency is bumped. To update it: set `lib.fakeHash`, run
  # the build, and paste the hash nix reports.
  zigDeps = zig.fetchDeps {
    inherit (finalAttrs) pname version src;
    fetchAll = true;
    hash = "sha256-yWUmqKxop3uCqvHBrb16pgAgA2O+0kholkY+M7Zftbk=";
  };

  postConfigure = ''
    # A writable copy rather than a symlink into the store: Zig writes cache
    # metadata alongside the fetched packages while it verifies them.
    cp -rLT ${finalAttrs.zigDeps} "$ZIG_GLOBAL_CACHE_DIR/p"
    chmod -R u+w "$ZIG_GLOBAL_CACHE_DIR/p"
  '';

  nativeBuildInputs = [ zig ];

  # The zig setup hook's check phase runs `zig build test`, which is the whole
  # suite. Nothing in it touches the network or the filesystem outside the build
  # directory, so it runs happily in the sandbox: every rebuild is a test run.
  doCheck = true;

  meta = {
    description = "Language Server Protocol implementation for SRF (Simple Record Format)";
    longDescription = ''
      Diagnostics and hover for SRF documents, using the srf library's own parser
      so the editor cannot disagree with the reference implementation. Reports
      parse errors, length-prefix declarations that do not match the bytes
      present, and keys whose type varies across records in one document.
    '';
    homepage = "https://git.lerch.org/lobo/srf-lsp";
    license = lib.licenses.mit;
    mainProgram = "srf-lsp";
    platforms = lib.platforms.unix;
  };
})