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| <ol class="chapter"><li class="chapter-item affix "><a href="about-this-guide.html">About this guide</a></li><li class="chapter-item affix "><a href="getting-started.html">Getting Started</a></li><li class="spacer"></li><li class="chapter-item affix "><li class="part-title">Building and debugging rustc</li><li class="chapter-item "><a href="building/how-to-build-and-run.html"><strong aria-hidden="true">1.</strong> How to Build and Run the Compiler</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="building/prerequisites.html"><strong aria-hidden="true">1.1.</strong> Prerequisites</a></li><li class="chapter-item "><a href="building/suggested.html"><strong aria-hidden="true">1.2.</strong> Suggested Workflows</a></li><li class="chapter-item "><a href="building/build-install-distribution-artifacts.html"><strong aria-hidden="true">1.3.</strong> Distribution artifacts</a></li><li class="chapter-item "><a href="building/compiler-documenting.html"><strong aria-hidden="true">1.4.</strong> Documenting Compiler</a></li><li class="chapter-item "><a href="rustdoc.html"><strong aria-hidden="true">1.5.</strong> Rustdoc overview</a></li><li class="chapter-item "><a href="building/new-target.html"><strong aria-hidden="true">1.6.</strong> Adding a new target</a></li></ol></li><li class="chapter-item "><a href="tests/intro.html"><strong aria-hidden="true">2.</strong> The compiler testing framework</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="tests/running.html"><strong aria-hidden="true">2.1.</strong> Running tests</a></li><li class="chapter-item "><a href="tests/adding.html"><strong aria-hidden="true">2.2.</strong> Adding new tests</a></li><li class="chapter-item "><a href="compiletest.html"><strong aria-hidden="true">2.3.</strong> Using compiletest commands to control test execution</a></li></ol></li><li class="chapter-item expanded "><a href="compiler-debugging.html" class="active"><strong aria-hidden="true">3.</strong> Debugging the Compiler</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="tracing.html"><strong aria-hidden="true">3.1.</strong> Using the tracing/logging instrumentation</a></li></ol></li><li class="chapter-item "><a href="profiling.html"><strong aria-hidden="true">4.</strong> Profiling the compiler</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="profiling/with_perf.html"><strong aria-hidden="true">4.1.</strong> with the linux perf tool</a></li><li class="chapter-item "><a href="profiling/wpa_profiling.html"><strong aria-hidden="true">4.2.</strong> with Windows Performance Analyzer</a></li></ol></li><li class="chapter-item "><a href="crates-io.html"><strong aria-hidden="true">5.</strong> crates.io Dependencies</a></li><li class="chapter-item affix "><li class="part-title">Contributing to Rust</li><li class="chapter-item "><a href="contributing.html"><strong aria-hidden="true">6.</strong> Introduction</a></li><li class="chapter-item "><a href="compiler-team.html"><strong aria-hidden="true">7.</strong> About the compiler team</a></li><li class="chapter-item "><a href="git.html"><strong aria-hidden="true">8.</strong> Using Git</a></li><li class="chapter-item "><a href="rustbot.html"><strong aria-hidden="true">9.</strong> Mastering @rustbot</a></li><li class="chapter-item "><a href="walkthrough.html"><strong aria-hidden="true">10.</strong> Walkthrough: a typical contribution</a></li><li class="chapter-item "><a href="bug-fix-procedure.html"><strong aria-hidden="true">11.</strong> Bug Fix Procedure</a></li><li class="chapter-item "><a href="implementing_new_features.html"><strong aria-hidden="true">12.</strong> Implementing new features</a></li><li class="chapter-item "><a href="stability.html"><strong aria-hidden="true">13.</strong> Stability attributes</a></li><li class="chapter-item "><a href="stabilization_guide.html"><strong aria-hidden="true">14.</strong> Stabilizing Features</a></li><li class="chapter-item "><a href="feature-gates.html"><strong aria-hidden="true">15.</strong> Feature Gates</a></li><li class="chapter-item "><a href="conventions.html"><strong aria-hidden="true">16.</strong> Coding conventions</a></li><li class="chapter-item "><a href="notification-groups/about.html"><strong aria-hidden="true">17.</strong> Notification groups</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="notification-groups/arm.html"><strong aria-hidden="true">17.1.</strong> ARM</a></li><li class="chapter-item "><a href="notification-groups/cleanup-crew.html"><strong aria-hidden="true">17.2.</strong> Cleanup Crew</a></li><li class="chapter-item "><a href="notification-groups/llvm.html"><strong aria-hidden="true">17.3.</strong> LLVM</a></li><li class="chapter-item "><a href="notification-groups/risc-v.html"><strong aria-hidden="true">17.4.</strong> RISC-V</a></li><li class="chapter-item "><a href="notification-groups/windows.html"><strong aria-hidden="true">17.5.</strong> Windows</a></li></ol></li><li class="chapter-item "><a href="licenses.html"><strong aria-hidden="true">18.</strong> Licenses</a></li><li class="chapter-item affix "><li class="part-title">High-level Compiler Architecture</li><li class="chapter-item "><a href="part-2-intro.html"><strong aria-hidden="true">19.</strong> Prologue</a></li><li class="chapter-item "><a href="overview.html"><strong aria-hidden="true">20.</strong> Overview of the Compiler</a></li><li class="chapter-item "><a href="compiler-src.html"><strong aria-hidden="true">21.</strong> The compiler source code</a></li><li class="chapter-item "><a href="building/bootstrapping.html"><strong aria-hidden="true">22.</strong> Bootstrapping</a></li><li class="chapter-item "><a href="query.html"><strong aria-hidden="true">23.</strong> Queries: demand-driven compilation</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="queries/query-evaluation-model-in-detail.html"><strong aria-hidden="true">23.1.</strong> The Query Evaluation Model in Detail</a></li><li class="chapter-item "><a href="queries/incremental-compilation.html"><strong aria-hidden="true">23.2.</strong> Incremental compilation</a></li><li class="chapter-item "><a href="queries/incremental-compilation-in-detail.html"><strong aria-hidden="true">23.3.</strong> Incremental compilation In Detail</a></li><li class="chapter-item "><a href="incrcomp-debugging.html"><strong aria-hidden="true">23.4.</strong> Debugging and Testing</a></li><li class="chapter-item "><a href="salsa.html"><strong aria-hidden="true">23.5.</strong> Salsa</a></li></ol></li><li class="chapter-item "><a href="memory.html"><strong aria-hidden="true">24.</strong> Memory Management in Rustc</a></li><li class="chapter-item "><a href="serialization.html"><strong aria-hidden="true">25.</strong> Serialization in Rustc</a></li><li class="chapter-item "><a href="parallel-rustc.html"><strong aria-hidden="true">26.</strong> Parallel Compilation</a></li><li class="chapter-item "><a href="rustdoc-internals.html"><strong aria-hidden="true">27.</strong> Rustdoc internals</a></li><li class="chapter-item affix "><li class="part-title">Source Code Representation</li><li class="chapter-item "><a href="part-3-intro.html"><strong aria-hidden="true">28.</strong> Prologue</a></li><li class="chapter-item "><a href="cli.html"><strong aria-hidden="true">29.</strong> Command-line arguments</a></li><li class="chapter-item "><a href="rustc-driver.html"><strong aria-hidden="true">30.</strong> The Rustc Driver and Interface</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="rustc-driver-interacting-with-the-ast.html"><strong aria-hidden="true">30.1.</strong> Ex: Type checking through rustc_interface</a></li><li class="chapter-item "><a href="rustc-driver-getting-diagnostics.html"><strong aria-hidden="true">30.2.</strong> Ex: Getting diagnostics through rustc_interface</a></li></ol></li><li class="chapter-item "><a href="syntax-intro.html"><strong aria-hidden="true">31.</strong> Syntax and the AST</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="the-parser.html"><strong aria-hidden="true">31.1.</strong> Lexing and Parsing</a></li><li class="chapter-item "><a href="macro-expansion.html"><strong aria-hidden="true">31.2.</strong> Macro expansion</a></li><li class="chapter-item "><a href="name-resolution.html"><strong aria-hidden="true">31.3.</strong> Name resolution</a></li><li class="chapter-item "><a href="test-implementation.html"><strong aria-hidden="true">31.4.</strong> #[test] Implementation</a></li><li class="chapter-item "><a href="panic-implementation.html"><strong aria-hidden="true">31.5.</strong> Panic Implementation</a></li><li class="chapter-item "><a href="ast-validation.html"><strong aria-hidden="true">31.6.</strong> AST Validation</a></li><li class="chapter-item "><a href="feature-gate-ck.html"><strong aria-hidden="true">31.7.</strong> Feature Gate Checking</a></li><li class="chapter-item "><a href="lang-items.html"><strong aria-hidden="true">31.8.</strong> Lang Items</a></li></ol></li><li class="chapter-item "><a href="hir.html"><strong aria-hidden="true">32.</strong> The HIR (High-level IR)</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="lowering.html"><strong aria-hidden="true">32.1.</strong> Lowering AST to HIR</a></li><li class="chapter-item "><a href="hir-debugging.html"><strong aria-hidden="true">32.2.</strong> Debugging</a></li></ol></li><li class="chapter-item "><a href="thir.html"><strong aria-hidden="true">33.</strong> The THIR (Typed High-level IR)</a></li><li class="chapter-item "><a href="mir/index.html"><strong aria-hidden="true">34.</strong> The MIR (Mid-level IR)</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="mir/construction.html"><strong aria-hidden="true">34.1.</strong> MIR construction</a></li><li class="chapter-item "><a href="mir/visitor.html"><strong aria-hidden="true">34.2.</strong> MIR visitor and traversal</a></li><li class="chapter-item "><a href="mir/passes.html"><strong aria-hidden="true">34.3.</strong> MIR passes: getting the MIR for a function</a></li></ol></li><li class="chapter-item "><a href="identifiers.html"><strong aria-hidden="true">35.</strong> Identifiers in the Compiler</a></li><li class="chapter-item "><a href="closure.html"><strong aria-hidden="true">36.</strong> Closure expansion</a></li><li class="chapter-item affix "><li class="part-title">Analysis</li><li class="chapter-item "><a href="part-4-intro.html"><strong aria-hidden="true">37.</strong> Prologue</a></li><li class="chapter-item "><a href="ty.html"><strong aria-hidden="true">38.</strong> The ty module: representing types</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="generics.html"><strong aria-hidden="true">38.1.</strong> Generics and substitutions</a></li><li class="chapter-item "><a href="ty-fold.html"><strong aria-hidden="true">38.2.</strong> TypeFolder and TypeFoldable</a></li><li class="chapter-item "><a href="generic_arguments.html"><strong aria-hidden="true">38.3.</strong> Generic arguments</a></li><li class="chapter-item "><a href="constants.html"><strong aria-hidden="true">38.4.</strong> Constants in the type system</a></li></ol></li><li class="chapter-item "><a href="type-inference.html"><strong aria-hidden="true">39.</strong> Type inference</a></li><li class="chapter-item "><a href="traits/resolution.html"><strong aria-hidden="true">40.</strong> Trait solving</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="early-late-bound.html"><strong aria-hidden="true">40.1.</strong> Early and Late Bound Parameters</a></li><li class="chapter-item "><a href="traits/hrtb.html"><strong aria-hidden="true">40.2.</strong> Higher-ranked trait bounds</a></li><li class="chapter-item "><a href="traits/caching.html"><strong aria-hidden="true">40.3.</strong> Caching subtleties</a></li><li class="chapter-item "><a href="traits/specialization.html"><strong aria-hidden="true">40.4.</strong> Specialization</a></li><li class="chapter-item "><a href="traits/chalk.html"><strong aria-hidden="true">40.5.</strong> Chalk-based trait solving</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="traits/lowering-to-logic.html"><strong aria-hidden="true">40.5.1.</strong> Lowering to logic</a></li><li class="chapter-item "><a href="traits/goals-and-clauses.html"><strong aria-hidden="true">40.5.2.</strong> Goals and clauses</a></li><li class="chapter-item "><a href="traits/canonical-queries.html"><strong aria-hidden="true">40.5.3.</strong> Canonical queries</a></li></ol></li></ol></li><li class="chapter-item "><a href="type-checking.html"><strong aria-hidden="true">41.</strong> Type checking</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="method-lookup.html"><strong aria-hidden="true">41.1.</strong> Method Lookup</a></li><li class="chapter-item "><a href="variance.html"><strong aria-hidden="true">41.2.</strong> Variance</a></li><li class="chapter-item "><a href="opaque-types-type-alias-impl-trait.html"><strong aria-hidden="true">41.3.</strong> Opaque Types</a></li></ol></li><li class="chapter-item "><a href="pat-exhaustive-checking.html"><strong aria-hidden="true">42.</strong> Pattern and Exhaustiveness Checking</a></li><li class="chapter-item "><a href="mir/dataflow.html"><strong aria-hidden="true">43.</strong> MIR dataflow</a></li><li class="chapter-item "><a href="borrow_check.html"><strong aria-hidden="true">44.</strong> The borrow checker</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="borrow_check/moves_and_initialization.html"><strong aria-hidden="true">44.1.</strong> Tracking moves and initialization</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="borrow_check/moves_and_initialization/move_paths.html"><strong aria-hidden="true">44.1.1.</strong> Move paths</a></li></ol></li><li class="chapter-item "><a href="borrow_check/type_check.html"><strong aria-hidden="true">44.2.</strong> MIR type checker</a></li><li class="chapter-item "><a href="borrow_check/region_inference.html"><strong aria-hidden="true">44.3.</strong> Region inference</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="borrow_check/region_inference/constraint_propagation.html"><strong aria-hidden="true">44.3.1.</strong> Constraint propagation</a></li><li class="chapter-item "><a href="borrow_check/region_inference/lifetime_parameters.html"><strong aria-hidden="true">44.3.2.</strong> Lifetime parameters</a></li><li class="chapter-item "><a href="borrow_check/region_inference/member_constraints.html"><strong aria-hidden="true">44.3.3.</strong> Member constraints</a></li><li class="chapter-item "><a href="borrow_check/region_inference/placeholders_and_universes.html"><strong aria-hidden="true">44.3.4.</strong> Placeholders and universes</a></li><li class="chapter-item "><a href="borrow_check/region_inference/closure_constraints.html"><strong aria-hidden="true">44.3.5.</strong> Closure constraints</a></li><li class="chapter-item "><a href="borrow_check/region_inference/error_reporting.html"><strong aria-hidden="true">44.3.6.</strong> Error reporting</a></li></ol></li><li class="chapter-item "><a href="borrow_check/two_phase_borrows.html"><strong aria-hidden="true">44.4.</strong> Two-phase-borrows</a></li></ol></li><li class="chapter-item "><a href="param_env.html"><strong aria-hidden="true">45.</strong> Parameter Environments</a></li><li class="chapter-item "><a href="diagnostics.html"><strong aria-hidden="true">46.</strong> Errors and Lints</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="diagnostics/sessiondiagnostic.html"><strong aria-hidden="true">46.1.</strong> Creating Errors With SessionDiagnostic</a></li><li class="chapter-item "><a href="diagnostics/lintstore.html"><strong aria-hidden="true">46.2.</strong> LintStore</a></li><li class="chapter-item "><a href="diagnostics/diagnostic-codes.html"><strong aria-hidden="true">46.3.</strong> Diagnostic Codes</a></li><li class="chapter-item "><a href="diagnostics/diagnostic-items.html"><strong aria-hidden="true">46.4.</strong> Diagnostic Items</a></li></ol></li><li class="chapter-item "><li class="part-title">MIR to Binaries</li><li class="chapter-item "><a href="part-5-intro.html"><strong aria-hidden="true">47.</strong> Prologue</a></li><li class="chapter-item "><a href="mir/optimizations.html"><strong aria-hidden="true">48.</strong> MIR optimizations</a></li><li class="chapter-item "><a href="mir/debugging.html"><strong aria-hidden="true">49.</strong> Debugging</a></li><li class="chapter-item "><a href="const-eval.html"><strong aria-hidden="true">50.</strong> Constant evaluation</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="miri.html"><strong aria-hidden="true">50.1.</strong> miri const evaluator</a></li></ol></li><li class="chapter-item "><a href="backend/monomorph.html"><strong aria-hidden="true">51.</strong> Monomorphization</a></li><li class="chapter-item "><a href="backend/lowering-mir.html"><strong aria-hidden="true">52.</strong> Lowering MIR</a></li><li class="chapter-item "><a href="backend/codegen.html"><strong aria-hidden="true">53.</strong> Code Generation</a><a 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aria-hidden="true">56.</strong> LLVM Source-Based Code Coverage</a></li><li class="chapter-item "><a href="sanitizers.html"><strong aria-hidden="true">57.</strong> Sanitizers Support</a></li><li class="chapter-item "><a href="debugging-support-in-rustc.html"><strong aria-hidden="true">58.</strong> Debugging Support in the Rust Compiler</a></li><li class="spacer"></li><li class="chapter-item affix "><a href="appendix/background.html">Appendix A: Background topics</a></li><li class="chapter-item affix "><a href="appendix/glossary.html">Appendix B: Glossary</a></li><li class="chapter-item affix "><a href="appendix/code-index.html">Appendix C: Code Index</a></li><li class="chapter-item affix "><a href="appendix/compiler-lecture.html">Appendix D: Compiler Lecture Series</a></li><li class="chapter-item affix "><a href="appendix/bibliography.html">Appendix E: Bibliography</a></li><li class="chapter-item affix "><a href="appendix/humorust.html">Appendix Z: HumorRust</a></li><li 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| <h1 id="debugging-the-compiler"><a class="header" href="#debugging-the-compiler">Debugging the compiler</a></h1> |
| <ul> |
| <li><a href="#configuring-the-compiler">Configuring the compiler</a></li> |
| <li><a href="#-z-flags"><code>-Z</code> flags</a></li> |
| <li><a href="#getting-a-backtrace">Getting a backtrace</a></li> |
| <li><a href="#getting-a-backtrace-for-errors">Getting a backtrace for errors</a></li> |
| <li><a href="#getting-logging-output">Getting logging output</a></li> |
| <li><a href="#formatting-graphviz-output-dot-files">Formatting Graphviz output (.dot files)</a></li> |
| <li><a href="#viewing-spanview-output-html-files">Viewing Spanview output (.html files)</a></li> |
| <li><a href="#narrowing-bisecting-regressions">Narrowing (Bisecting) Regressions</a></li> |
| <li><a href="#downloading-artifacts-from-rusts-ci">Downloading Artifacts from Rust's CI</a></li> |
| <li><a href="#debugging-type-layouts">Debugging type layouts</a></li> |
| </ul> |
| <p>This chapter contains a few tips to debug the compiler. These tips aim to be |
| useful no matter what you are working on. Some of the other chapters have |
| advice about specific parts of the compiler (e.g. the <a href="./incrcomp-debugging.html">Queries Debugging and |
| Testing chapter</a> or the <a href="./backend/debugging.html">LLVM Debugging |
| chapter</a>).</p> |
| <h2 id="configuring-the-compiler"><a class="header" href="#configuring-the-compiler">Configuring the compiler</a></h2> |
| <p>By default, rustc is built without most debug information. To enable debug info, |
| set <code>debug = true</code> in your config.toml.</p> |
| <p>Setting <code>debug = true</code> turns on many different debug options (e.g., <code>debug-assertions</code>, |
| <code>debug-logging</code>, etc.) which can be individually tweaked if you want to, but many people |
| simply set <code>debug = true</code>. Check out the comments in config.toml.example for more info.</p> |
| <p>You will need to rebuild the compiler once you've changed any configuration options.</p> |
| <h2 id="-z-flags"><a class="header" href="#-z-flags"><code>-Z</code> flags</a></h2> |
| <p>The compiler has a bunch of <code>-Z</code> flags. These are unstable flags that are only |
| enabled on nightly. Many of them are useful for debugging. To get a full listing |
| of <code>-Z</code> flags, use <code>-Z help</code>.</p> |
| <p>One useful flag is <code>-Z verbose</code>, which generally enables printing more info that |
| could be useful for debugging.</p> |
| <h2 id="getting-a-backtrace"><a class="header" href="#getting-a-backtrace">Getting a backtrace</a></h2> |
| <p>When you have an ICE (panic in the compiler), you can set |
| <code>RUST_BACKTRACE=1</code> to get the stack trace of the <code>panic!</code> like in |
| normal Rust programs. IIRC backtraces <strong>don't work</strong> on MinGW, |
| sorry. If you have trouble or the backtraces are full of <code>unknown</code>, |
| you might want to find some way to use Linux, Mac, or MSVC on Windows.</p> |
| <p>In the default configuration (without <code>debug</code> set to <code>true</code>), you don't have line numbers |
| enabled, so the backtrace looks like this:</p> |
| <pre><code class="language-text">stack backtrace: |
| 0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace |
| 1: std::sys_common::backtrace::_print |
| 2: std::panicking::default_hook::{{closure}} |
| 3: std::panicking::default_hook |
| 4: std::panicking::rust_panic_with_hook |
| 5: std::panicking::begin_panic |
| (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) |
| 32: rustc_typeck::check_crate |
| 33: <std::thread::local::LocalKey<T>>::with |
| 34: <std::thread::local::LocalKey<T>>::with |
| 35: rustc::ty::context::TyCtxt::create_and_enter |
| 36: rustc_driver::driver::compile_input |
| 37: rustc_driver::run_compiler |
| </code></pre> |
| <p>If you set <code>debug = true</code>, you will get line numbers for the stack trace. |
| Then the backtrace will look like this:</p> |
| <pre><code class="language-text">stack backtrace: |
| (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) |
| at /home/user/rust/compiler/rustc_typeck/src/check/cast.rs:110 |
| 7: rustc_typeck::check::cast::CastCheck::check |
| at /home/user/rust/compiler/rustc_typeck/src/check/cast.rs:572 |
| at /home/user/rust/compiler/rustc_typeck/src/check/cast.rs:460 |
| at /home/user/rust/compiler/rustc_typeck/src/check/cast.rs:370 |
| (~~~~ LINES REMOVED BY ME FOR BREVITY ~~~~) |
| 33: rustc_driver::driver::compile_input |
| at /home/user/rust/compiler/rustc_driver/src/driver.rs:1010 |
| at /home/user/rust/compiler/rustc_driver/src/driver.rs:212 |
| 34: rustc_driver::run_compiler |
| at /home/user/rust/compiler/rustc_driver/src/lib.rs:253 |
| </code></pre> |
| <h2 id="getting-a-backtrace-for-errors"><a class="header" href="#getting-a-backtrace-for-errors">Getting a backtrace for errors</a></h2> |
| <p>If you want to get a backtrace to the point where the compiler emits an |
| error message, you can pass the <code>-Z treat-err-as-bug=n</code>, which will make |
| the compiler panic on the <code>nth</code> error on <code>delay_span_bug</code>. If you leave |
| off <code>=n</code>, the compiler will assume <code>1</code> for <code>n</code> and thus panic on the |
| first error it encounters.</p> |
| <p>This can also help when debugging <code>delay_span_bug</code> calls - it will make |
| the first <code>delay_span_bug</code> call panic, which will give you a useful backtrace.</p> |
| <p>For example:</p> |
| <pre><code class="language-bash">$ cat error.rs |
| </code></pre> |
| <pre><pre class="playground"><code class="language-rust">fn main() { |
| 1 + (); |
| } |
| </code></pre></pre> |
| <pre><code class="language-bash">$ rustc +stage1 error.rs |
| error[E0277]: cannot add `()` to `{integer}` |
| --> error.rs:2:7 |
| | |
| 2 | 1 + (); |
| | ^ no implementation for `{integer} + ()` |
| | |
| = help: the trait `Add<()>` is not implemented for `{integer}` |
| |
| error: aborting due to previous error |
| </code></pre> |
| <p>Now, where does the error above come from?</p> |
| <pre><code class="language-bash">$ RUST_BACKTRACE=1 rustc +stage1 error.rs -Z treat-err-as-bug |
| error[E0277]: the trait bound `{integer}: std::ops::Add<()>` is not satisfied |
| --> error.rs:2:7 |
| | |
| 2 | 1 + (); |
| | ^ no implementation for `{integer} + ()` |
| | |
| = help: the trait `std::ops::Add<()>` is not implemented for `{integer}` |
| |
| error: internal compiler error: unexpected panic |
| |
| note: the compiler unexpectedly panicked. this is a bug. |
| |
| note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports |
| |
| note: rustc 1.24.0-dev running on x86_64-unknown-linux-gnu |
| |
| note: run with `RUST_BACKTRACE=1` for a backtrace |
| |
| thread 'rustc' panicked at 'encountered error with `-Z treat_err_as_bug', |
| /home/user/rust/compiler/rustc_errors/src/lib.rs:411:12 |
| note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose |
| backtrace. |
| stack backtrace: |
| (~~~ IRRELEVANT PART OF BACKTRACE REMOVED BY ME ~~~) |
| 7: rustc::traits::error_reporting::<impl rustc::infer::InferCtxt<'a, 'tcx>> |
| ::report_selection_error |
| at /home/user/rust/compiler/rustc_middle/src/traits/error_reporting.rs:823 |
| 8: rustc::traits::error_reporting::<impl rustc::infer::InferCtxt<'a, 'tcx>> |
| ::report_fulfillment_errors |
| at /home/user/rust/compiler/rustc_middle/src/traits/error_reporting.rs:160 |
| at /home/user/rust/compiler/rustc_middle/src/traits/error_reporting.rs:112 |
| 9: rustc_typeck::check::FnCtxt::select_obligations_where_possible |
| at /home/user/rust/compiler/rustc_typeck/src/check/mod.rs:2192 |
| (~~~ IRRELEVANT PART OF BACKTRACE REMOVED BY ME ~~~) |
| 36: rustc_driver::run_compiler |
| at /home/user/rust/compiler/rustc_driver/src/lib.rs:253 |
| </code></pre> |
| <p>Cool, now I have a backtrace for the error!</p> |
| <h2 id="getting-logging-output"><a class="header" href="#getting-logging-output">Getting logging output</a></h2> |
| <p>The compiler uses the <a href="https://docs.rs/tracing"><code>tracing</code></a> crate for logging.</p> |
| <p>For details see <a href="./tracing.html">the guide section on tracing</a></p> |
| <h2 id="formatting-graphviz-output-dot-files"><a class="header" href="#formatting-graphviz-output-dot-files">Formatting Graphviz output (.dot files)</a></h2> |
| <p>Some compiler options for debugging specific features yield graphviz graphs - |
| e.g. the <code>#[rustc_mir(borrowck_graphviz_postflow="suffix.dot")]</code> attribute |
| dumps various borrow-checker dataflow graphs.</p> |
| <p>These all produce <code>.dot</code> files. To view these files, install graphviz (e.g. |
| <code>apt-get install graphviz</code>) and then run the following commands:</p> |
| <pre><code class="language-bash">$ dot -T pdf maybe_init_suffix.dot > maybe_init_suffix.pdf |
| $ firefox maybe_init_suffix.pdf # Or your favorite pdf viewer |
| </code></pre> |
| <h2 id="viewing-spanview-output-html-files"><a class="header" href="#viewing-spanview-output-html-files">Viewing Spanview output (.html files)</a></h2> |
| <p>In addition to <a href="#formatting-graphviz-output-dot-files">graphviz output</a>, MIR debugging |
| flags include an option to generate a MIR representation called <code>Spanview</code> that |
| uses HTML to highlight code regions in the original source code and display |
| compiler metadata associated with each region. |
| <a href="./mir/debugging.html"><code>-Z dump-mir-spanview</code></a>, for example, highlights spans |
| associated with each MIR <code>Statement</code>, <code>Terminator</code>, and/or <code>BasicBlock</code>.</p> |
| <p>These <code>.html</code> files use CSS features to dynamically expand spans obscured by |
| overlapping spans, and native tooltips (based on the HTML <code>title</code> attribute) to |
| reveal the actual MIR elements, as text.</p> |
| <p>To view these files, simply use a modern browser, or a CSS-capable HTML preview |
| feature in a modern IDE. (The default HTML preview pane in <em>VS Code</em> is known to |
| work, for instance.)</p> |
| <h2 id="narrowing-bisecting-regressions"><a class="header" href="#narrowing-bisecting-regressions">Narrowing (Bisecting) Regressions</a></h2> |
| <p>The <a href="https://github.com/rust-lang/cargo-bisect-rustc">cargo-bisect-rustc</a> tool can be used as a quick and easy way to |
| find exactly which PR caused a change in <code>rustc</code> behavior. It automatically |
| downloads <code>rustc</code> PR artifacts and tests them against a project you provide |
| until it finds the regression. You can then look at the PR to get more context |
| on <em>why</em> it was changed. See <a href="https://github.com/rust-lang/cargo-bisect-rustc/blob/master/TUTORIAL.md">this tutorial</a> on how to use |
| it.</p> |
| <h2 id="downloading-artifacts-from-rusts-ci"><a class="header" href="#downloading-artifacts-from-rusts-ci">Downloading Artifacts from Rust's CI</a></h2> |
| <p>The <a href="https://github.com/kennytm/rustup-toolchain-install-master">rustup-toolchain-install-master</a> tool by kennytm can be used to |
| download the artifacts produced by Rust's CI for a specific SHA1 -- this |
| basically corresponds to the successful landing of some PR -- and then sets |
| them up for your local use. This also works for artifacts produced by <code>@bors try</code>. This is helpful when you want to examine the resulting build of a PR |
| without doing the build yourself.</p> |
| <h2 id="debugging-type-layouts"><a class="header" href="#debugging-type-layouts">Debugging type layouts</a></h2> |
| <p>The (permanently) unstable <code>#[rustc_layout]</code> attribute can be used to dump |
| the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_target/abi/struct.Layout.html"><code>Layout</code></a> of the type it is attached to. For example:</p> |
| <pre><pre class="playground"><code class="language-rust"> |
| <span class="boring">#![allow(unused)] |
| </span>#![feature(rustc_attrs)] |
| |
| <span class="boring">fn main() { |
| </span>#[rustc_layout(debug)] |
| type T<'a> = &'a u32; |
| <span class="boring">} |
| </span></code></pre></pre> |
| <p>Will emit the following:</p> |
| <pre><code class="language-text">error: layout_of(&'a u32) = Layout { |
| fields: Primitive, |
| variants: Single { |
| index: 0, |
| }, |
| abi: Scalar( |
| Scalar { |
| value: Pointer, |
| valid_range: 1..=18446744073709551615, |
| }, |
| ), |
| largest_niche: Some( |
| Niche { |
| offset: Size { |
| raw: 0, |
| }, |
| scalar: Scalar { |
| value: Pointer, |
| valid_range: 1..=18446744073709551615, |
| }, |
| }, |
| ), |
| align: AbiAndPrefAlign { |
| abi: Align { |
| pow2: 3, |
| }, |
| pref: Align { |
| pow2: 3, |
| }, |
| }, |
| size: Size { |
| raw: 8, |
| }, |
| } |
| --> src/lib.rs:4:1 |
| | |
| 4 | type T<'a> = &'a u32; |
| | ^^^^^^^^^^^^^^^^^^^^^ |
| |
| error: aborting due to previous error |
| </code></pre> |
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