Switch from ld (the default linker) to using lld for GNU Linux targets (

#65898)

Copies changes from vercel/turborepo#8166, and
updates contributing documentation to include the installation of lld.

> **What's wrong with `ld`?** It's very slow and uses a lot of memory.
>
> **Why `lld`?** It's fast, mature, and well-supported. Meta and Google
use it for all their linking workloads. We're already using it for macos
and x86-64 Windows. There is [ongoing work to make it the default for
rustc](rust-lang/rust#71515), and it already
is default on a few platforms.
>
> **Why not `mold`?** Mold is generally faster, but the margin is slim
enough for our workloads that it doesn't really matter. Mold only
recently got support for LTO, doesn't support v0 rust symbol demanging,
doesn't support BOLT (though we don't use that yet), etc. Mold is
maturing quickly, but `lld` still seems like the "safer" choice.

.cargo/config.toml

@@ -22,11 +22,20 @@ rustflags = ["-C", "target-feature=+crt-static"]
 [target.aarch64-pc-windows-msvc]
 linker = "rust-lld"
 
-[target.aarch64-apple-darwin]
+[target.'cfg(target_os = "macos")']
 linker = "rust-lld"
 
-[target.aarch64-unknown-linux-gnu]
-linker = "aarch64-linux-gnu-gcc"
+[target.'cfg(all(target_os = "linux", target_env = "gnu"))']
+rustflags = [
+  "--cfg",
+  "tokio_unstable",
+  "-Zshare-generics=y",
+  "-Zthreads=8",
+  "-Zunstable-options",
+  "-Csymbol-mangling-version=v0",
+  "-Clinker-flavor=gnu-lld-cc",
+  "-Clink-self-contained=+linker",
+]
 
 [target.aarch64-unknown-linux-musl]
 linker = "aarch64-linux-musl-gcc"

.github/actions/setup-rust/action.yml

@@ -16,6 +16,11 @@ runs:
         rustflags: ''
         cache: false
 
+    - name: 'Install LLD (LLVM Linker) for Linux'
+      if: runner.os == 'Linux'
+      shell: bash
+      run: sudo apt-get -y update && sudo apt-get install -y lld
+
     - name: 'Add cargo problem matchers'
       shell: bash
       run: echo "::add-matcher::${{ github.action_path }}/matchers.json"

contributing/core/developing.md

@@ -4,10 +4,21 @@
 - All pull requests should be opened against `canary`.
 - The changes on the `canary` branch are published to the `@canary` tag on npm regularly.
 
-To develop locally:
+## Dependencies
+
+- Install Rust and Cargo via [rustup](https://rustup.rs).
+- Install the [GitHub CLI](https://github.com/cli/cli#installation).
+- Enable pnpm:
+  ```
+  corepack enable pnpm
+  ```
+- (Linux) Install LLD, the LLVM linker:
+  ```
+  sudo apt install lld
+  ```
+
+## Local Development
 
-1. Install Rust and Cargo via [rustup](https://rustup.rs).
-1. Install the [GitHub CLI](https://github.com/cli/cli#installation).
 1. Clone the Next.js repository (download only recent commits for faster clone):
    ```
    gh repo clone vercel/next.js -- --filter=blob:none --branch canary --single-branch
@@ -16,10 +27,6 @@ To develop locally:
    ```
    git checkout -b MY_BRANCH_NAME origin/canary
    ```
-1. Enable pnpm:
-   ```
-   corepack enable pnpm
-   ```
 1. Install the dependencies with:
    ```
    pnpm install