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Add more comments about proc macro resolution

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This commit is contained in:
Jonas Schievink 2020-09-28 13:02:28 +02:00
parent e799dbe5d7
commit e88e4fbb7b
1 changed files with 20 additions and 0 deletions
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20
crates/hir_def/src/nameres/collector.rs
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@ -203,6 +203,10 @@ struct DefCollector<'a> {
unexpanded_attribute_macros: Vec<DeriveDirective>,
mod_dirs: FxHashMap<LocalModuleId, ModDir>,
cfg_options: &'a CfgOptions,
/// List of procedural macros defined by this crate. This is read from the dynamic library
/// built by the build system, and is the list of proc. macros we can actually expand. It is
/// empty when proc. macro support is disabled (in which case we still do name resolution for
/// them).
proc_macros: Vec<(Name, ProcMacroExpander)>,
exports_proc_macros: bool,
from_glob_import: PerNsGlobImports,
@ -279,6 +283,22 @@ impl DefCollector<'_> {
}
}
/// Adds a definition of procedural macro `name` to the root module.
///
/// # Notes on procedural macro resolution
///
/// Procedural macro functionality is provided by the build system: It has to build the proc
/// macro and pass the resulting dynamic library to rust-analyzer.
///
/// When procedural macro support is enabled, the list of proc macros exported by a crate is
/// known before we resolve names in the crate. This list is stored in `self.proc_macros` and is
/// derived from the dynamic library.
///
/// However, we *also* would like to be able to at least *resolve* macros on our own, without
/// help by the build system. So, when the macro isn't found in `self.proc_macros`, we instead
/// use a dummy expander that always errors. This comes with the drawback of macros potentially
/// going out of sync with what the build system sees (since we resolve using VFS state, but
/// Cargo builds only on-disk files). We could and probably should add diagnostics for that.
fn resolve_proc_macro(&mut self, name: &Name) {
self.exports_proc_macros = true;
let macro_def = match self.proc_macros.iter().find(|(n, _)| n == name) {