suggest: large suggestion to flake.nix

flake.nix

@@ -1,62 +1,72 @@
 # Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
 # SPDX-License-Identifier: Apache-2.0
-
 {
+  description = "A dev environment with the tools needed to work on libdatadog.";
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/release-25.11";
-
-    # cross-platform convenience
     flake-utils.url = "github:numtide/flake-utils";
 
-    # backwards compatibility with nix-build and nix-shell
-    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
-
     # pinned, exact upstream Rust toolchains
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+
+    # backwards compatibility with nix-build and nix-shell
+    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
   };
 
-  outputs = { self, nixpkgs, flake-utils, flake-compat, rust-overlay }:
-    # resolve for all platforms in turn
-    flake-utils.lib.eachDefaultSystem (system:
-      let
-        # packages for this system platform, with the rust-overlay applied
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    rust-overlay,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (
+      system: let
         pkgs = import nixpkgs {
           inherit system;
-          overlays = [ (import rust-overlay) ];
+          overlays = [(import rust-overlay)];
         };
+        mkShell = rust-toolchain:
+          pkgs.mkShell {
+            name = "libdatadog-devshell";
+            # The stdenv cc-wrapper injects -D_FORTIFY_SOURCE, which glibc rejects
+            # when compiling without optimization. Some build scripts (e.g.
+            # spawn_worker's trampoline.c) compile C at -O0 with -Werror, so the
+            # resulting fortify #warning becomes a hard error. Disable fortify
+            # hardening in the shell so those builds succeed.
+            hardeningDisable = [
+              "fortify"
+              "fortify3"
+            ];
 
-        # A devshell for a given Rust toolchain (read from a toolchain file via
-        # rust-overlay), with the rest of the build dependencies.
-        mkDevShell = rust: pkgs.stdenv.mkDerivation {
-          name = "libdatadog-devshell";
-
-          # The stdenv cc-wrapper injects -D_FORTIFY_SOURCE, which glibc rejects
-          # when compiling without optimization. Some build scripts (e.g.
-          # spawn_worker's trampoline.c) compile C at -O0 with -Werror, so the
-          # resulting fortify #warning becomes a hard error. Disable fortify
-          # hardening in the shell so those builds succeed.
-          hardeningDisable = [ "fortify" "fortify3" ];
-
-          nativeBuildInputs = [
-            rust            # rustc + cargo + rustfmt + clippy, pinned via toolchain file
-            pkgs.rust-cbindgen
-            pkgs.cmake
-            pkgs.autoconf
-            pkgs.automake
-            pkgs.libtool
-          ];
-        };
+            packages =
+              [rust-toolchain]
+              ++ (with pkgs; [
+                rust-cbindgen
+                cargo-nextest
+                cmake
+                autoconf
+                automake
+                libtool
+                alejandra
+              ]);
+            env = {
+              # Required by rust-analyzer
+              RUST_SRC_PATH = "${rust-toolchain}/lib/rustlib/src/rust/library";
+            };
+          };
       in {
         # Default: the pinned stable toolchain (single source of truth is
         # ./rust-toolchain.toml), matching CI and rustup.
-        devShells.default = mkDevShell (pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml);
+        # Use with `nix develop`
+        devShells.default = mkShell (pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml);
 
         # Nightly toolchain (./nightly-toolchain.toml) for the jobs that
-        # genuinely need a nightly compiler. Use with `nix develop .#nightly`.
-        devShells.nightly = mkDevShell (pkgs.rust-bin.fromRustupToolchainFile ./nightly-toolchain.toml);
+        # genuinely need a nightly compiler.
+        # Use with `nix develop .#nightly`.
+        devShells.nightly = mkShell (pkgs.rust-bin.fromRustupToolchainFile ./nightly-toolchain.toml);
       }
     );
 }

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
 channel = "1.87.0"
-components = ["rustfmt", "clippy"]
+components = ["clippy", "rust-src"]
 profile = "minimal"