rust/compiler/rustc_interface/src/callbacks.rs

//! Throughout the compiler tree, there are several places which want to have
//! access to state or queries while being inside crates that are dependencies
//! of `rustc_middle`. To facilitate this, we have the
//! `rustc_data_structures::AtomicRef` type, which allows us to setup a global
//! static which can then be set in this file at program startup.
//!
//! See `SPAN_TRACK` for an example of how to set things up.
//!
//! The functions in this file should fall back to the default set in their
//! origin crate when the `TyCtxt` is not present in TLS.

use std::fmt;

use rustc_errors::DiagInner;
use rustc_middle::dep_graph::{DepNodeIndex, QuerySideEffect, TaskDepsRef};
use rustc_middle::ty::tls;
use rustc_span::Symbol;

fn track_span_parent(def_id: rustc_span::def_id::LocalDefId) {
    tls::with_context_opt(|icx| {
        if let Some(icx) = icx {
            // `track_span_parent` gets called a lot from HIR lowering code.
            // Skip doing anything if we aren't tracking dependencies.
            let tracks_deps = match icx.task_deps {
                TaskDepsRef::Allow(..) => true,
                TaskDepsRef::EvalAlways | TaskDepsRef::Ignore | TaskDepsRef::Forbid => false,
            };
            if tracks_deps {
                let _span = icx.tcx.source_span(def_id);
                // Sanity check: relative span's parent must be an absolute span.
                debug_assert_eq!(_span.data_untracked().parent, None);
            }
        }
    })
}

/// This is a callback from `rustc_errors` as it cannot access the implicit state
/// in `rustc_middle` otherwise. It is used when diagnostic messages are
/// emitted and stores them in the current query, if there is one.
fn track_diagnostic<R>(diagnostic: DiagInner, f: &mut dyn FnMut(DiagInner) -> R) -> R {
    tls::with_context_opt(|icx| {
        if let Some(icx) = icx {
            icx.tcx.dep_graph.record_diagnostic(icx.tcx, &diagnostic);

            // Diagnostics are tracked, we can ignore the dependency.
            let icx = tls::ImplicitCtxt { task_deps: TaskDepsRef::Ignore, ..*icx };
            tls::enter_context(&icx, move || (*f)(diagnostic))
        } else {
            // In any other case, invoke diagnostics anyway.
            (*f)(diagnostic)
        }
    })
}

fn track_feature(feature: Symbol) {
    tls::with_context_opt(|icx| {
        let Some(icx) = icx else {
            return;
        };
        let tcx = icx.tcx;

        if let Some(dep_node_index) = tcx.sess.used_features.lock().get(&feature).copied() {
            tcx.dep_graph.read_index(DepNodeIndex::from_u32(dep_node_index));
        } else {
            let dep_node_index = tcx
                .dep_graph
                .encode_side_effect(tcx, QuerySideEffect::CheckFeature { symbol: feature });
            tcx.sess.used_features.lock().insert(feature, dep_node_index.as_u32());
            tcx.dep_graph.read_index(dep_node_index);
        }
    })
}

/// This is a callback from `rustc_hir` as it cannot access the implicit state
/// in `rustc_middle` otherwise.
fn def_id_debug(def_id: rustc_hir::def_id::DefId, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    write!(f, "DefId({}:{}", def_id.krate, def_id.index.index())?;
    tls::with_opt(|opt_tcx| {
        if let Some(tcx) = opt_tcx {
            write!(f, " ~ {}", tcx.def_path_debug_str(def_id))?;
        }
        Ok(())
    })?;
    write!(f, ")")
}

/// Sets up the callbacks in prior crates which we want to refer to the
/// TyCtxt in.
pub fn setup_callbacks() {
    rustc_span::SPAN_TRACK.swap(&(track_span_parent as fn(_)));
    rustc_hir::def_id::DEF_ID_DEBUG.swap(&(def_id_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
    rustc_errors::TRACK_DIAGNOSTIC.swap(&(track_diagnostic as _));
    rustc_feature::TRACK_FEATURE.swap(&(track_feature as _));
}