https://errorvault.dev/tags/macro_rules/ Recent content in Macro_rules on ErrorVault — Developer Error Code Dictionary Hugo en-us Sun, 09 Aug 2026 03:08:04 +0800 https://errorvault.dev/rust/rust-e0438-expected-semicolon-after-expression/ Sun, 09 Aug 2026 03:08:04 +0800 https://errorvault.dev/rust/rust-e0438-expected-semicolon-after-expression/ <h2 id="1-symptoms">1. Symptoms</h2> <p>When Rust compiler error E0438 occurs, the compiler produces a diagnostic message indicating that it expected a semicolon (<code>;</code>) or assignment operator (<code>=</code>) after encountering an expression. This typically manifests when macro-generated code produces an incomplete statement that lacks proper termination.</p> <p>The error manifests with a message structure similar to the following:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#282a36;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-fallback" data-lang="fallback"><span style="display:flex;"><span>error[E0438]: expected `;` or `=` after expression </span></span><span style="display:flex;"><span> --&gt; src/main.rs:12:5 </span></span><span style="display:flex;"><span> | </span></span><span style="display:flex;"><span>12 | some_macro!(arg1 arg2) </span></span><span style="display:flex;"><span> | ^^^^^^^^^^^^^^^^^^^^^ expected `;` or `=` </span></span></code></pre></div><p>In proc-macro contexts, the error may appear with slightly different wording but maintains the core semantics of expression termination failure. The error points to the macro invocation site rather than the macro definition itself, since the problem manifests during macro expansion evaluation.</p>