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| <h1 id="remarks-on-perma-unstable-features"><a class="header" href="#remarks-on-perma-unstable-features">Remarks on perma unstable features</a></h1> |
| <h2 id="rustc_private"><a class="header" href="#rustc_private"><code>rustc_private</code></a></h2> |
| <h3 id="overview"><a class="header" href="#overview">Overview</a></h3> |
| <p>The <code>rustc_private</code> feature allows external crates to use compiler internals.</p> |
| <h3 id="using-rustc-private-with-official-toolchains"><a class="header" href="#using-rustc-private-with-official-toolchains">Using <code>rustc-private</code> with Official Toolchains</a></h3> |
| <p>When using the <code>rustc_private</code> feature with official Rust toolchains distributed via rustup, you need to install two additional components:</p> |
| <ol> |
| <li><strong><code>rustc-dev</code></strong>: Provides compiler libraries</li> |
| <li><strong><code>llvm-tools</code></strong>: Provides LLVM libraries required for linking</li> |
| </ol> |
| <h4 id="installation-steps"><a class="header" href="#installation-steps">Installation Steps</a></h4> |
| <p>Install both components using rustup:</p> |
| <pre><code class="language-text">rustup component add rustc-dev llvm-tools |
| </code></pre> |
| <h4 id="common-error"><a class="header" href="#common-error">Common Error</a></h4> |
| <p>Without the <code>llvm-tools</code> component, you'll encounter linking errors like:</p> |
| <pre><code class="language-text">error: linking with `cc` failed: exit status: 1 |
| | |
| = note: rust-lld: error: unable to find library -lLLVM-{version} |
| </code></pre> |
| <h3 id="using-rustc-private-with-custom-toolchains"><a class="header" href="#using-rustc-private-with-custom-toolchains">Using <code>rustc-private</code> with Custom Toolchains</a></h3> |
| <p>For custom-built toolchains or environments not using rustup, additional configuration is typically required:</p> |
| <h4 id="requirements"><a class="header" href="#requirements">Requirements</a></h4> |
| <ul> |
| <li>LLVM libraries must be available in your system's library search paths</li> |
| <li>The LLVM version must match the one used to build your Rust toolchain</li> |
| </ul> |
| <h4 id="troubleshooting-steps"><a class="header" href="#troubleshooting-steps">Troubleshooting Steps</a></h4> |
| <ol> |
| <li><strong>Check LLVM installation</strong>: Verify LLVM is installed and accessible</li> |
| <li><strong>Configure library paths</strong>: You may need to set environment variables: |
| <pre><code class="language-text">export LD_LIBRARY_PATH=/path/to/llvm/lib:$LD_LIBRARY_PATH |
| </code></pre> |
| </li> |
| <li><strong>Check version compatibility</strong>: Ensure your LLVM version is compatible with your Rust toolchain</li> |
| </ol> |
| <h3 id="additional-resources"><a class="header" href="#additional-resources">Additional Resources</a></h3> |
| <ul> |
| <li><a href="https://github.com/rust-lang/rust/issues/137421">GitHub Issue #137421</a>: Explains that <code>rustc_private</code> linker failures often occur because <code>llvm-tools</code> is not installed</li> |
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