From fd7f08a43cdd04242d75012daf683f526ddee389 Mon Sep 17 00:00:00 2001
From: Alex Bates <alex@bates64.com>
Date: Fri, 7 Aug 2026 22:20:15 +0100
Subject: [PATCH] use nightly rust and improve dev build time

---
 Cargo.toml | 11 +++++++++++
 flake.nix  | 34 +++++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 293921f..a38e912 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,17 @@ edition = "2021"
 name = "server"
 path = "src/main.rs"
 
+[profile.dev]
+debug = "line-tables-only"
+
+# We never step into dependencies, and their debuginfo dominates link time.
+[profile.dev.package."*"]
+debug = 0
+
+[profile.debugging]
+inherits = "dev"
+debug = "full"
+
 [dependencies]
 axum = "0.8"
 maud = { version = "0.27", features = ["axum"] }
diff --git a/flake.nix b/flake.nix
index 040c26b..80af8e7 100644
--- a/flake.nix
+++ b/flake.nix
@@ -31,6 +31,19 @@
               "clippy"
             ];
           };
+          devToolchain = pkgs.rust-bin.selectLatestNightlyWith (
+            toolchain:
+            toolchain.default.override {
+              extensions = [
+                "rust-src"
+                "rust-analyzer"
+                "clippy"
+              ]
+              ++ lib.optionals useCranelift [ "rustc-codegen-cranelift-preview" ];
+            }
+          );
+          useCranelift = pkgs.stdenv.hostPlatform.isx86_64 || pkgs.stdenv.hostPlatform.isAarch64;
+          useMold = pkgs.stdenv.isLinux;
           rustBuildInputs = [
             pkgs.openssl
             pkgs.libiconv
@@ -80,13 +93,24 @@
           devShells.default = pkgs.mkShell {
             name = "starhaven-dev";
             buildInputs = rustBuildInputs;
-            nativeBuildInputs = with pkgs; [
-              rustToolchain
-              sqlx-cli
-            ];
+            nativeBuildInputs = [
+              devToolchain
+              pkgs.sqlx-cli
+            ]
+            ++ lib.optionals useMold [ pkgs.mold ];
             shellHook = ''
               # For rust-analyzer 'hover' tooltips to work.
-              export RUST_SRC_PATH="${rustToolchain}/lib/rustlib/src/rust/library";
+              export RUST_SRC_PATH="${devToolchain}/lib/rustlib/src/rust/library";
+
+              # parallel frontend stops paying off after 8 threads
+              rustc_threads=$(( $(nproc) < 8 ? $(nproc) : 8 ))
+
+              export RUSTFLAGS="${lib.optionalString useMold "-Clink-arg=-fuse-ld=mold "}-Zthreads=$rustc_threads"
+            ''
+            + lib.optionalString useCranelift ''
+              export CARGO_UNSTABLE_CODEGEN_BACKEND=true
+              export CARGO_PROFILE_DEV_CODEGEN_BACKEND=cranelift
+              export CARGO_PROFILE_DEBUGGING_CODEGEN_BACKEND=llvm
             '';
           };
         };
-- 
2.51.2