rustc_interface: Add a new query pre_configure

It partially expands crate attributes before the main expansion pass (without modifying the crate), and the produced preliminary crate attribute list is used for querying a few attributes that are required very early.

Crate-level cfg attributes are then expanded normally during the main expansion pass, like attributes on any other nodes.

Author: petrochenkov

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -8,14 +8,20 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
 use thin_vec::thin_vec;
 
-pub fn inject(krate: &mut ast::Crate, resolver: &mut dyn ResolverExpand, sess: &Session) {
+pub fn inject(
+    krate: &mut ast::Crate,
+    pre_configured_attrs: &[ast::Attribute],
+    resolver: &mut dyn ResolverExpand,
+    sess: &Session,
+) -> usize {
+    let orig_num_items = krate.items.len();
     let edition = sess.parse_sess.edition;
 
     // the first name in this list is the crate name of the crate with the prelude
-    let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
-        return;
-    } else if sess.contains_name(&krate.attrs, sym::no_std) {
-        if sess.contains_name(&krate.attrs, sym::compiler_builtins) {
+    let names: &[Symbol] = if sess.contains_name(pre_configured_attrs, sym::no_core) {
+        return 0;
+    } else if sess.contains_name(pre_configured_attrs, sym::no_std) {
+        if sess.contains_name(pre_configured_attrs, sym::compiler_builtins) {
             &[sym::core]
         } else {
             &[sym::core, sym::compiler_builtins]
@@ -84,4 +90,5 @@ pub fn inject(krate: &mut ast::Crate, resolver: &mut dyn ResolverExpand, sess: &
     );
 
     krate.items.insert(0, use_item);
+    krate.items.len() - orig_num_items
 }

compiler/rustc_driver_impl/src/lib.rs

@@ -353,7 +353,7 @@ fn run_compiler(
 
             {
                 let plugins = queries.register_plugins()?;
-                let (_, lint_store) = &*plugins.borrow();
+                let (.., lint_store) = &*plugins.borrow();
 
                 // Lint plugins are registered; now we can process command line flags.
                 if sess.opts.describe_lints {

compiler/rustc_expand/src/base.rs

@@ -1004,6 +1004,7 @@ pub struct ExpansionData {
 pub struct ExtCtxt<'a> {
     pub sess: &'a Session,
     pub ecfg: expand::ExpansionConfig<'a>,
+    pub num_standard_library_imports: usize,
     pub reduced_recursion_limit: Option<Limit>,
     pub root_path: PathBuf,
     pub resolver: &'a mut dyn ResolverExpand,
@@ -1032,6 +1033,7 @@ impl<'a> ExtCtxt<'a> {
         ExtCtxt {
             sess,
             ecfg,
+            num_standard_library_imports: 0,
             reduced_recursion_limit: None,
             resolver,
             lint_store,

compiler/rustc_expand/src/config.rs

@@ -24,7 +24,6 @@ use rustc_session::Session;
 use rustc_span::edition::{Edition, ALL_EDITIONS};
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
-use thin_vec::ThinVec;
 
 /// A folder that strips out items that do not belong in the current configuration.
 pub struct StripUnconfigured<'a> {
@@ -37,7 +36,7 @@ pub struct StripUnconfigured<'a> {
     pub lint_node_id: NodeId,
 }
 
-fn get_features(sess: &Session, krate_attrs: &[ast::Attribute]) -> Features {
+pub fn features(sess: &Session, krate_attrs: &[Attribute]) -> Features {
     fn feature_removed(sess: &Session, span: Span, reason: Option<&str>) {
         sess.emit_err(FeatureRemoved {
             span,
@@ -191,33 +190,16 @@ fn get_features(sess: &Session, krate_attrs: &[ast::Attribute]) -> Features {
     features
 }
 
-/// `cfg_attr`-process the crate's attributes and compute the crate's features.
-pub fn features(sess: &Session, krate: &mut ast::Crate, lint_node_id: NodeId) -> Features {
-    let mut strip_unconfigured =
-        StripUnconfigured { sess, features: None, config_tokens: false, lint_node_id };
-
-    let mut unconfigured_attrs = krate.attrs.clone();
-    let diag = &sess.parse_sess.span_diagnostic;
-    let err_count = diag.err_count();
-
-    krate.attrs.flat_map_in_place(|attr| strip_unconfigured.process_cfg_attr(&attr));
-    if !strip_unconfigured.in_cfg(&krate.attrs) {
-        // The entire crate is unconfigured.
-        krate.attrs = ast::AttrVec::new();
-        krate.items = ThinVec::new();
-        Features::default()
-    } else {
-        let features = get_features(sess, &krate.attrs);
-        if err_count == diag.err_count() {
-            // Avoid reconfiguring malformed `cfg_attr`s.
-            strip_unconfigured.features = Some(&features);
-            // Run configuration again, this time with features available
-            // so that we can perform feature-gating.
-            unconfigured_attrs.flat_map_in_place(|attr| strip_unconfigured.process_cfg_attr(&attr));
-            strip_unconfigured.in_cfg(&unconfigured_attrs);
-        }
-        features
-    }
+pub fn pre_configure_attrs(sess: &Session, attrs: &[Attribute]) -> ast::AttrVec {
+    let strip_unconfigured = StripUnconfigured {
+        sess,
+        features: None,
+        config_tokens: false,
+        lint_node_id: ast::CRATE_NODE_ID,
+    };
+    let attrs: ast::AttrVec =
+        attrs.iter().flat_map(|attr| strip_unconfigured.process_cfg_attr(attr)).collect();
+    if strip_unconfigured.in_cfg(&attrs) { attrs } else { ast::AttrVec::new() }
 }
 
 #[macro_export]

compiler/rustc_expand/src/expand.rs

@@ -1038,6 +1038,9 @@ trait InvocationCollectorNode: HasAttrs + HasNodeId + Sized {
     ) -> Result<Self::OutputTy, Self> {
         Ok(noop_flat_map(node, collector))
     }
+    fn expand_cfg_false(&mut self, collector: &mut InvocationCollector<'_, '_>, span: Span) {
+        collector.cx.emit_err(RemoveNodeNotSupported { span, descr: Self::descr() });
+    }
 }
 
 impl InvocationCollectorNode for P<ast::Item> {
@@ -1378,6 +1381,11 @@ impl InvocationCollectorNode for ast::Crate {
     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
         noop_visit_crate(self, visitor)
     }
+    fn expand_cfg_false(&mut self, collector: &mut InvocationCollector<'_, '_>, _span: Span) {
+        self.attrs.clear();
+        // Standard prelude imports are left in the crate for backward compatibility.
+        self.items.truncate(collector.cx.num_standard_library_imports);
+    }
 }
 
 impl InvocationCollectorNode for P<ast::Ty> {
@@ -1756,7 +1764,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                             continue;
                         }
 
-                        self.cx.emit_err(RemoveNodeNotSupported { span, descr: Node::descr() });
+                        node.expand_cfg_false(self, span);
                         continue;
                     }
                     sym::cfg_attr => {

compiler/rustc_interface/src/passes.rs

@@ -3,7 +3,6 @@ use crate::interface::{Compiler, Result};
 use crate::proc_macro_decls;
 use crate::util;
 
-use ast::CRATE_NODE_ID;
 use rustc_ast::{self as ast, visit};
 use rustc_borrowck as mir_borrowck;
 use rustc_codegen_ssa::traits::CodegenBackend;
@@ -76,22 +75,14 @@ pub fn register_plugins<'a>(
     sess: &'a Session,
     metadata_loader: &'a dyn MetadataLoader,
     register_lints: impl Fn(&Session, &mut LintStore),
-    krate: &mut ast::Crate,
+    pre_configured_attrs: &[ast::Attribute],
     crate_name: Symbol,
 ) -> Result<LintStore> {
-    sess.time("attributes_injection", || {
-        rustc_builtin_macros::cmdline_attrs::inject(
-            krate,
-            &sess.parse_sess,
-            &sess.opts.unstable_opts.crate_attr,
-        )
-    });
-
-    let features = rustc_expand::config::features(sess, krate, CRATE_NODE_ID);
     // these need to be set "early" so that expansion sees `quote` if enabled.
+    let features = rustc_expand::config::features(sess, pre_configured_attrs);
     sess.init_features(features);
 
-    let crate_types = util::collect_crate_types(sess, &krate.attrs);
+    let crate_types = util::collect_crate_types(sess, pre_configured_attrs);
     sess.init_crate_types(crate_types);
 
     let stable_crate_id = StableCrateId::new(
@@ -117,8 +108,9 @@ pub fn register_plugins<'a>(
     let mut lint_store = rustc_lint::new_lint_store(sess.enable_internal_lints());
     register_lints(sess, &mut lint_store);
 
-    let registrars = sess
-        .time("plugin_loading", || plugin::load::load_plugins(sess, metadata_loader, &krate.attrs));
+    let registrars = sess.time("plugin_loading", || {
+        plugin::load::load_plugins(sess, metadata_loader, pre_configured_attrs)
+    });
     sess.time("plugin_registration", || {
         let mut registry = plugin::Registry { lint_store: &mut lint_store };
         for registrar in registrars {
@@ -173,19 +165,28 @@ impl LintStoreExpand for LintStoreExpandImpl<'_> {
 /// harness if one is to be provided, injection of a dependency on the
 /// standard library and prelude, and name resolution.
 #[instrument(level = "trace", skip(krate, resolver))]
-fn configure_and_expand(mut krate: ast::Crate, resolver: &mut Resolver<'_, '_>) -> ast::Crate {
+fn configure_and_expand(
+    mut krate: ast::Crate,
+    pre_configured_attrs: &[ast::Attribute],
+    resolver: &mut Resolver<'_, '_>,
+) -> ast::Crate {
     let tcx = resolver.tcx();
     let sess = tcx.sess;
     let lint_store = unerased_lint_store(tcx);
     let crate_name = tcx.crate_name(LOCAL_CRATE);
     pre_expansion_lint(sess, lint_store, tcx.registered_tools(()), &krate, crate_name);
     rustc_builtin_macros::register_builtin_macros(resolver);
 
-    sess.time("crate_injection", || {
-        rustc_builtin_macros::standard_library_imports::inject(&mut krate, resolver, sess)
+    let num_standard_library_imports = sess.time("crate_injection", || {
+        rustc_builtin_macros::standard_library_imports::inject(
+            &mut krate,
+            pre_configured_attrs,
+            resolver,
+            sess,
+        )
     });
 
-    util::check_attr_crate_type(sess, &krate.attrs, &mut resolver.lint_buffer());
+    util::check_attr_crate_type(sess, pre_configured_attrs, &mut resolver.lint_buffer());
 
     // Expand all macros
     krate = sess.time("macro_expand_crate", || {
@@ -222,7 +223,7 @@ fn configure_and_expand(mut krate: ast::Crate, resolver: &mut Resolver<'_, '_>)
 
         // Create the config for macro expansion
         let features = sess.features_untracked();
-        let recursion_limit = get_recursion_limit(&krate.attrs, sess);
+        let recursion_limit = get_recursion_limit(pre_configured_attrs, sess);
         let cfg = rustc_expand::expand::ExpansionConfig {
             features: Some(features),
             recursion_limit,
@@ -235,6 +236,7 @@ fn configure_and_expand(mut krate: ast::Crate, resolver: &mut Resolver<'_, '_>)
 
         let lint_store = LintStoreExpandImpl(lint_store);
         let mut ecx = ExtCtxt::new(sess, cfg, resolver, Some(&lint_store));
+        ecx.num_standard_library_imports = num_standard_library_imports;
         // Expand macros now!
         let krate = sess.time("expand_crate", || ecx.monotonic_expander().expand_crate(krate));
 
@@ -557,9 +559,9 @@ fn resolver_for_lowering<'tcx>(
 ) -> &'tcx Steal<(ty::ResolverAstLowering, Lrc<ast::Crate>)> {
     let arenas = Resolver::arenas();
     let _ = tcx.registered_tools(()); // Uses `crate_for_resolver`.
-    let krate = tcx.crate_for_resolver(()).steal();
-    let mut resolver = Resolver::new(tcx, &krate, &arenas);
-    let krate = configure_and_expand(krate, &mut resolver);
+    let (krate, pre_configured_attrs) = tcx.crate_for_resolver(()).steal();
+    let mut resolver = Resolver::new(tcx, &pre_configured_attrs, krate.spans.inner_span, &arenas);
+    let krate = configure_and_expand(krate, &pre_configured_attrs, &mut resolver);
 
     // Make sure we don't mutate the cstore from here on.
     tcx.untracked().cstore.leak();

compiler/rustc_interface/src/queries.rs

@@ -88,8 +88,9 @@ pub struct Queries<'tcx> {
 
     dep_graph_future: Query<Option<DepGraphFuture>>,
     parse: Query<ast::Crate>,
+    pre_configure: Query<(ast::Crate, ast::AttrVec)>,
     crate_name: Query<Symbol>,
-    register_plugins: Query<(ast::Crate, Lrc<LintStore>)>,
+    register_plugins: Query<(ast::Crate, ast::AttrVec, Lrc<LintStore>)>,
     dep_graph: Query<DepGraph>,
     // This just points to what's in `gcx_cell`.
     gcx: Query<&'tcx GlobalCtxt<'tcx>>,
@@ -106,6 +107,7 @@ impl<'tcx> Queries<'tcx> {
             hir_arena: WorkerLocal::new(|_| rustc_hir::Arena::default()),
             dep_graph_future: Default::default(),
             parse: Default::default(),
+            pre_configure: Default::default(),
             crate_name: Default::default(),
             register_plugins: Default::default(),
             dep_graph: Default::default(),
@@ -133,17 +135,36 @@ impl<'tcx> Queries<'tcx> {
             .compute(|| passes::parse(self.session()).map_err(|mut parse_error| parse_error.emit()))
     }
 
-    pub fn register_plugins(&self) -> Result<QueryResult<'_, (ast::Crate, Lrc<LintStore>)>> {
+    pub fn pre_configure(&self) -> Result<QueryResult<'_, (ast::Crate, ast::AttrVec)>> {
+        self.pre_configure.compute(|| {
+            let mut krate = self.parse()?.steal();
+
+            let sess = self.session();
+            rustc_builtin_macros::cmdline_attrs::inject(
+                &mut krate,
+                &sess.parse_sess,
+                &sess.opts.unstable_opts.crate_attr,
+            );
+
+            let pre_configured_attrs =
+                rustc_expand::config::pre_configure_attrs(sess, &krate.attrs);
+            Ok((krate, pre_configured_attrs))
+        })
+    }
+
+    pub fn register_plugins(
+        &self,
+    ) -> Result<QueryResult<'_, (ast::Crate, ast::AttrVec, Lrc<LintStore>)>> {
         self.register_plugins.compute(|| {
             let crate_name = *self.crate_name()?.borrow();
-            let mut krate = self.parse()?.steal();
+            let (krate, pre_configured_attrs) = self.pre_configure()?.steal();
 
             let empty: &(dyn Fn(&Session, &mut LintStore) + Sync + Send) = &|_, _| {};
             let lint_store = passes::register_plugins(
                 self.session(),
                 &*self.codegen_backend().metadata_loader(),
                 self.compiler.register_lints.as_deref().unwrap_or_else(|| empty),
-                &mut krate,
+                &pre_configured_attrs,
                 crate_name,
             )?;
 
@@ -154,17 +175,17 @@ impl<'tcx> Queries<'tcx> {
             // called, which happens within passes::register_plugins().
             self.dep_graph_future().ok();
 
-            Ok((krate, Lrc::new(lint_store)))
+            Ok((krate, pre_configured_attrs, Lrc::new(lint_store)))
         })
     }
 
     fn crate_name(&self) -> Result<QueryResult<'_, Symbol>> {
         self.crate_name.compute(|| {
             Ok({
-                let parse_result = self.parse()?;
-                let krate = parse_result.borrow();
+                let pre_configure_result = self.pre_configure()?;
+                let (_, pre_configured_attrs) = &*pre_configure_result.borrow();
                 // parse `#[crate_name]` even if `--crate-name` was passed, to make sure it matches.
-                find_crate_name(self.session(), &krate.attrs)
+                find_crate_name(self.session(), pre_configured_attrs)
             })
         })
     }
@@ -188,7 +209,7 @@ impl<'tcx> Queries<'tcx> {
     pub fn global_ctxt(&'tcx self) -> Result<QueryResult<'_, &'tcx GlobalCtxt<'tcx>>> {
         self.gcx.compute(|| {
             let crate_name = *self.crate_name()?.borrow();
-            let (krate, lint_store) = self.register_plugins()?.steal();
+            let (krate, pre_configured_attrs, lint_store) = self.register_plugins()?.steal();
 
             let sess = self.session();
 
@@ -215,7 +236,7 @@ impl<'tcx> Queries<'tcx> {
                 feed.crate_name(crate_name);
 
                 let feed = tcx.feed_unit_query();
-                feed.crate_for_resolver(tcx.arena.alloc(Steal::new(krate)));
+                feed.crate_for_resolver(tcx.arena.alloc(Steal::new((krate, pre_configured_attrs))));
                 feed.metadata_loader(
                     tcx.arena.alloc(Steal::new(self.codegen_backend().metadata_loader())),
                 );

compiler/rustc_middle/src/arena.rs

@@ -36,7 +36,7 @@ macro_rules! arena_types {
             )>,
             [] output_filenames: std::sync::Arc<rustc_session::config::OutputFilenames>,
             [] metadata_loader: rustc_data_structures::steal::Steal<Box<rustc_session::cstore::MetadataLoaderDyn>>,
-            [] crate_for_resolver: rustc_data_structures::steal::Steal<rustc_ast::ast::Crate>,
+            [] crate_for_resolver: rustc_data_structures::steal::Steal<(rustc_ast::Crate, rustc_ast::AttrVec)>,
             [] resolutions: rustc_middle::ty::ResolverGlobalCtxt,
             [decode] unsafety_check_result: rustc_middle::mir::UnsafetyCheckResult,
             [decode] code_region: rustc_middle::mir::coverage::CodeRegion,

compiler/rustc_middle/src/query/mod.rs

@@ -2116,7 +2116,7 @@ rustc_queries! {
         desc { "raw operations for metadata file access" }
     }
 
-    query crate_for_resolver((): ()) -> &'tcx Steal<rustc_ast::ast::Crate> {
+    query crate_for_resolver((): ()) -> &'tcx Steal<(rustc_ast::Crate, rustc_ast::AttrVec)> {
         feedable
         no_hash
         desc { "the ast before macro expansion and name resolution" }