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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 "><a href="compiler-debugging.html"><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 expanded "><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 expanded "><a href="name-resolution.html" class="active"><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="name-resolution"><a class="header" href="#name-resolution">Name resolution</a></h1> |
| <ul> |
| <li><a href="#basics">Basics</a></li> |
| <li><a href="#namespaces">Namespaces</a></li> |
| <li><a href="#scopes-and-ribs">Scopes and ribs</a></li> |
| <li><a href="#overall-strategy">Overall strategy</a></li> |
| <li><a href="#speculative-crate-loading">Speculative crate loading</a></li> |
| <li><a href="#todo-16">TODO: #16</a></li> |
| </ul> |
| <p>In the previous chapters, we saw how the AST is built with all macros expanded. |
| We saw how doing that requires doing some name resolution to resolve imports |
| and macro names. In this chapter, we show how this is actually done and more.</p> |
| <p>In fact, we don't do full name resolution during macro expansion -- we only |
| resolve imports and macros at that time. This is required to know what to even |
| expand. Later, after we have the whole AST, we do full name resolution to |
| resolve all names in the crate. This happens in <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/index.html"><code>rustc_resolve::late</code></a>. |
| Unlike during macro expansion, in this late expansion, we only need to try to |
| resolve a name once, since no new names can be added. If we fail to resolve a |
| name now, then it is a compiler error.</p> |
| <p>Name resolution can be complex. There are a few different namespaces (e.g. |
| macros, values, types, lifetimes), and names may be valid at different (nested) |
| scopes. Also, different types of names can fail to be resolved differently, and |
| failures can happen differently at different scopes. For example, for a module |
| scope, failure means no unexpanded macros and no unresolved glob imports in |
| that module. On the other hand, in a function body, failure requires that a |
| name be absent from the block we are in, all outer scopes, and the global |
| scope.</p> |
| <h2 id="basics"><a class="header" href="#basics">Basics</a></h2> |
| <p>In our programs we can refer to variables, types, functions, etc, by giving them |
| a name. These names are not always unique. For example, take this valid Rust |
| program:</p> |
| <pre><pre class="playground"><code class="language-rust"> |
| <span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>type x = u32; |
| let x: x = 1; |
| let y: x = 2; |
| <span class="boring">} |
| </span></code></pre></pre> |
| <p>How do we know on line 3 whether <code>x</code> is a type (u32) or a value (1)? These |
| conflicts are resolved during name resolution. In this specific case, name |
| resolution defines that type names and variable names live in separate |
| namespaces and therefore can co-exist.</p> |
| <p>The name resolution in Rust is a two-phase process. In the first phase, which runs |
| during macro expansion, we build a tree of modules and resolve imports. Macro |
| expansion and name resolution communicate with each other via the |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast_lowering/trait.ResolverAstLowering.html"><code>ResolverAstLowering</code></a> trait.</p> |
| <p>The input to the second phase is the syntax tree, produced by parsing input |
| files and expanding macros. This phase produces links from all the names in the |
| source to relevant places where the name was introduced. It also generates |
| helpful error messages, like typo suggestions, traits to import or lints about |
| unused items.</p> |
| <p>A successful run of the second phase (<a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/struct.Resolver.html#method.resolve_crate"><code>Resolver::resolve_crate</code></a>) creates kind |
| of an index the rest of the compilation may use to ask about the present names |
| (through the <code>hir::lowering::Resolver</code> interface).</p> |
| <p>The name resolution lives in the <code>rustc_resolve</code> crate, with the meat in |
| <code>lib.rs</code> and some helpers or symbol-type specific logic in the other modules.</p> |
| <h2 id="namespaces"><a class="header" href="#namespaces">Namespaces</a></h2> |
| <p>Different kind of symbols live in different namespaces ‒ e.g. types don't |
| clash with variables. This usually doesn't happen, because variables start with |
| lower-case letter while types with upper case one, but this is only a |
| convention. This is legal Rust code that'll compile (with warnings):</p> |
| <pre><pre class="playground"><code class="language-rust"> |
| <span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>type x = u32; |
| let x: x = 1; |
| let y: x = 2; // See? x is still a type here. |
| <span class="boring">} |
| </span></code></pre></pre> |
| <p>To cope with this, and with slightly different scoping rules for these |
| namespaces, the resolver keeps them separated and builds separate structures for |
| them.</p> |
| <p>In other words, when the code talks about namespaces, it doesn't mean the module |
| hierarchy, it's types vs. values vs. macros.</p> |
| <h2 id="scopes-and-ribs"><a class="header" href="#scopes-and-ribs">Scopes and ribs</a></h2> |
| <p>A name is visible only in certain area in the source code. This forms a |
| hierarchical structure, but not necessarily a simple one ‒ if one scope is |
| part of another, it doesn't mean the name visible in the outer one is also |
| visible in the inner one, or that it refers to the same thing.</p> |
| <p>To cope with that, the compiler introduces the concept of Ribs. This is |
| abstraction of a scope. Every time the set of visible names potentially changes, |
| a new rib is pushed onto a stack. The places where this can happen includes for |
| example:</p> |
| <ul> |
| <li>The obvious places ‒ curly braces enclosing a block, function boundaries, |
| modules.</li> |
| <li>Introducing a let binding ‒ this can shadow another binding with the same |
| name.</li> |
| <li>Macro expansion border ‒ to cope with macro hygiene.</li> |
| </ul> |
| <p>When searching for a name, the stack of ribs is traversed from the innermost |
| outwards. This helps to find the closest meaning of the name (the one not |
| shadowed by anything else). The transition to outer rib may also change the |
| rules what names are usable ‒ if there are nested functions (not closures), |
| the inner one can't access parameters and local bindings of the outer one, |
| even though they should be visible by ordinary scoping rules. An example:</p> |
| <pre><pre class="playground"><code class="language-rust"> |
| <span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>fn do_something<T: Default>(val: T) { // <- New rib in both types and values (1) |
| // `val` is accessible, as is the helper function |
| // `T` is accessible |
| let helper = || { // New rib on `helper` (2) and another on the block (3) |
| // `val` is accessible here |
| }; // End of (3) |
| // `val` is accessible, `helper` variable shadows `helper` function |
| fn helper() { // <- New rib in both types and values (4) |
| // `val` is not accessible here, (4) is not transparent for locals) |
| // `T` is not accessible here |
| } // End of (4) |
| let val = T::default(); // New rib (5) |
| // `val` is the variable, not the parameter here |
| } // End of (5), (2) and (1) |
| <span class="boring">} |
| </span></code></pre></pre> |
| <p>Because the rules for different namespaces are a bit different, each namespace |
| has its own independent rib stack that is constructed in parallel to the others. |
| In addition, there's also a rib stack for local labels (e.g. names of loops or |
| blocks), which isn't a full namespace in its own right.</p> |
| <h2 id="overall-strategy"><a class="header" href="#overall-strategy">Overall strategy</a></h2> |
| <p>To perform the name resolution of the whole crate, the syntax tree is traversed |
| top-down and every encountered name is resolved. This works for most kinds of |
| names, because at the point of use of a name it is already introduced in the Rib |
| hierarchy.</p> |
| <p>There are some exceptions to this. Items are bit tricky, because they can be |
| used even before encountered ‒ therefore every block needs to be first scanned |
| for items to fill in its Rib.</p> |
| <p>Other, even more problematic ones, are imports which need recursive fixed-point |
| resolution and macros, that need to be resolved and expanded before the rest of |
| the code can be processed.</p> |
| <p>Therefore, the resolution is performed in multiple stages.</p> |
| <h2 id="speculative-crate-loading"><a class="header" href="#speculative-crate-loading">Speculative crate loading</a></h2> |
| <p>To give useful errors, rustc suggests importing paths into scope if they're |
| not found. How does it do this? It looks through every module of every crate |
| and looks for possible matches. This even includes crates that haven't yet |
| been loaded!</p> |
| <p>Loading crates for import suggestions that haven't yet been loaded is called |
| <em>speculative crate loading</em>, because any errors it encounters shouldn't be |
| reported: resolve decided to load them, not the user. The function that does |
| this is <code>lookup_import_candidates</code> and lives in |
| <code>rustc_resolve/src/diagnostics.rs</code>.</p> |
| <p>To tell the difference between speculative loads and loads initiated by the |
| user, resolve passes around a <code>record_used</code> parameter, which is <code>false</code> when |
| the load is speculative.</p> |
| <h2 id="todo-a-hrefhttpsgithubcomrust-langrustc-dev-guideissues1616a"><a class="header" href="#todo-a-hrefhttpsgithubcomrust-langrustc-dev-guideissues1616a">TODO: <a href="https://github.com/rust-lang/rustc-dev-guide/issues/16">#16</a></a></h2> |
| <p>This is a result of the first pass of learning the code. It is definitely |
| incomplete and not detailed enough. It also might be inaccurate in places. |
| Still, it probably provides useful first guidepost to what happens in there.</p> |
| <ul> |
| <li>What exactly does it link to and how is that published and consumed by |
| following stages of compilation?</li> |
| <li>Who calls it and how it is actually used.</li> |
| <li>Is it a pass and then the result is only used, or can it be computed |
| incrementally (e.g. for RLS)?</li> |
| <li>The overall strategy description is a bit vague.</li> |
| <li>Where does the name <code>Rib</code> come from?</li> |
| <li>Does this thing have its own tests, or is it tested only as part of some e2e |
| testing?</li> |
| </ul> |
| |
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