Auto merge of #108221 - petrochenkov:cratecfg, r=michaelwoerister

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 on the crate itself are then expanded normally during the main expansion pass, like attributes on any other nodes.
This is a continuation of #92473 and one more step to very unstable crate-level proc macro attributes maybe actually working.

Previously crate attributes were pre-configured simultaneously with feature extraction, and then written directly into `ast::Crate`.

compiler/rustc_builtin_macros/src/cmdline_attrs.rs

@@ -6,7 +6,7 @@ use rustc_ast::{self as ast, AttrItem, AttrStyle};
 use rustc_session::parse::ParseSess;
 use rustc_span::FileName;
 
-pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -> ast::Crate {
+pub fn inject(krate: &mut ast::Crate, parse_sess: &ParseSess, attrs: &[String]) {
     for raw_attr in attrs {
         let mut parser = rustc_parse::new_parser_from_source_str(
             parse_sess,
@@ -36,6 +36,4 @@ pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -
             start_span.to(end_span),
         ));
     }
-
-    krate
 }

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -43,14 +43,14 @@ struct CollectProcMacros<'a> {
 }
 
 pub fn inject(
+    krate: &mut ast::Crate,
     sess: &Session,
     resolver: &mut dyn ResolverExpand,
-    mut krate: ast::Crate,
     is_proc_macro_crate: bool,
     has_proc_macro_decls: bool,
     is_test_crate: bool,
     handler: &rustc_errors::Handler,
-) -> ast::Crate {
+) {
     let ecfg = ExpansionConfig::default("proc_macro".to_string());
     let mut cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
@@ -64,22 +64,20 @@ pub fn inject(
     };
 
     if has_proc_macro_decls || is_proc_macro_crate {
-        visit::walk_crate(&mut collect, &krate);
+        visit::walk_crate(&mut collect, krate);
     }
     let macros = collect.macros;
 
     if !is_proc_macro_crate {
-        return krate;
+        return;
     }
 
     if is_test_crate {
-        return krate;
+        return;
     }
 
     let decls = mk_decls(&mut cx, &macros);
     krate.items.push(decls);
-
-    krate
 }
 
 impl<'a> CollectProcMacros<'a> {

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -9,17 +9,19 @@ use rustc_span::DUMMY_SP;
 use thin_vec::thin_vec;
 
 pub fn inject(
-    mut krate: ast::Crate,
+    krate: &mut ast::Crate,
+    pre_configured_attrs: &[ast::Attribute],
     resolver: &mut dyn ResolverExpand,
     sess: &Session,
-) -> ast::Crate {
+) -> 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 attr::contains_name(&krate.attrs, sym::no_core) {
-        return krate;
-    } else if attr::contains_name(&krate.attrs, sym::no_std) {
-        if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
+    let names: &[Symbol] = if attr::contains_name(pre_configured_attrs, sym::no_core) {
+        return 0;
+    } else if attr::contains_name(pre_configured_attrs, sym::no_std) {
+        if attr::contains_name(pre_configured_attrs, sym::compiler_builtins) {
             &[sym::core]
         } else {
             &[sym::core, sym::compiler_builtins]
@@ -88,6 +90,5 @@ pub fn inject(
     );
 
     krate.items.insert(0, use_item);
-
-    krate
+    krate.items.len() - orig_num_items
 }

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -37,7 +37,7 @@ struct TestCtxt<'a> {
 
 /// Traverse the crate, collecting all the test functions, eliding any
 /// existing main functions, and synthesizing a main test harness
-pub fn inject(sess: &Session, resolver: &mut dyn ResolverExpand, krate: &mut ast::Crate) {
+pub fn inject(krate: &mut ast::Crate, sess: &Session, resolver: &mut dyn ResolverExpand) {
     let span_diagnostic = sess.diagnostic();
     let panic_strategy = sess.panic_strategy();
     let platform_panic_strategy = sess.target.panic_strategy;

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

@@ -1002,6 +1002,7 @@ 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,
@@ -1030,6 +1031,7 @@ 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,
@@ -191,39 +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,
-    mut krate: ast::Crate,
-    lint_node_id: NodeId,
-) -> (ast::Crate, Features) {
-    let mut strip_unconfigured =
-        StripUnconfigured { sess, features: None, config_tokens: false, lint_node_id };
-
-    let unconfigured_attrs = krate.attrs.clone();
-    let diag = &sess.parse_sess.span_diagnostic;
-    let err_count = diag.err_count();
-    let features = match strip_unconfigured.configure_krate_attrs(krate.attrs) {
-        None => {
-            // The entire crate is unconfigured.
-            krate.attrs = ast::AttrVec::new();
-            krate.items = ThinVec::new();
-            Features::default()
-        }
-        Some(attrs) => {
-            krate.attrs = attrs;
-            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.
-                strip_unconfigured.configure_krate_attrs(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,
     };
-    (krate, features)
+    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]
@@ -254,11 +230,6 @@ impl<'a> StripUnconfigured<'a> {
         }
     }
 
-    fn configure_krate_attrs(&self, mut attrs: ast::AttrVec) -> Option<ast::AttrVec> {
-        attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
-        self.in_cfg(&attrs).then_some(attrs)
-    }
-
     /// Performs cfg-expansion on `stream`, producing a new `AttrTokenStream`.
     /// This is only used during the invocation of `derive` proc-macros,
     /// which require that we cfg-expand their entire input.
@@ -281,7 +252,7 @@ impl<'a> StripUnconfigured<'a> {
             .iter()
             .flat_map(|tree| match tree.clone() {
                 AttrTokenTree::Attributes(mut data) => {
-                    data.attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
+                    data.attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
 
                     if self.in_cfg(&data.attrs) {
                         data.tokens = LazyAttrTokenStream::new(
@@ -319,12 +290,16 @@ impl<'a> StripUnconfigured<'a> {
     /// the syntax of any `cfg_attr` is incorrect.
     fn process_cfg_attrs<T: HasAttrs>(&self, node: &mut T) {
         node.visit_attrs(|attrs| {
-            attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
+            attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
         });
     }
 
-    fn process_cfg_attr(&self, attr: Attribute) -> Vec<Attribute> {
-        if attr.has_name(sym::cfg_attr) { self.expand_cfg_attr(attr, true) } else { vec![attr] }
+    fn process_cfg_attr(&self, attr: &Attribute) -> Vec<Attribute> {
+        if attr.has_name(sym::cfg_attr) {
+            self.expand_cfg_attr(attr, true)
+        } else {
+            vec![attr.clone()]
+        }
     }
 
     /// Parse and expand a single `cfg_attr` attribute into a list of attributes
@@ -334,9 +309,9 @@ impl<'a> StripUnconfigured<'a> {
     /// Gives a compiler warning when the `cfg_attr` contains no attributes and
     /// is in the original source file. Gives a compiler error if the syntax of
     /// the attribute is incorrect.
-    pub(crate) fn expand_cfg_attr(&self, attr: Attribute, recursive: bool) -> Vec<Attribute> {
+    pub(crate) fn expand_cfg_attr(&self, attr: &Attribute, recursive: bool) -> Vec<Attribute> {
         let Some((cfg_predicate, expanded_attrs)) =
-            rustc_parse::parse_cfg_attr(&attr, &self.sess.parse_sess) else {
+            rustc_parse::parse_cfg_attr(attr, &self.sess.parse_sess) else {
                 return vec![];
             };
 
@@ -365,10 +340,10 @@ impl<'a> StripUnconfigured<'a> {
             //  `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
             expanded_attrs
                 .into_iter()
-                .flat_map(|item| self.process_cfg_attr(self.expand_cfg_attr_item(&attr, item)))
+                .flat_map(|item| self.process_cfg_attr(&self.expand_cfg_attr_item(attr, item)))
                 .collect()
         } else {
-            expanded_attrs.into_iter().map(|item| self.expand_cfg_attr_item(&attr, item)).collect()
+            expanded_attrs.into_iter().map(|item| self.expand_cfg_attr_item(attr, item)).collect()
         }
     }
 

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> {
@@ -1688,7 +1696,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         res
     }
 
-    fn expand_cfg_attr(&self, node: &mut impl HasAttrs, attr: ast::Attribute, pos: usize) {
+    fn expand_cfg_attr(&self, node: &mut impl HasAttrs, attr: &ast::Attribute, pos: usize) {
         node.visit_attrs(|attrs| {
             // Repeated `insert` calls is inefficient, but the number of
             // insertions is almost always 0 or 1 in practice.
@@ -1712,7 +1720,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         Default::default()
                     }
                     sym::cfg_attr => {
-                        self.expand_cfg_attr(&mut node, attr, pos);
+                        self.expand_cfg_attr(&mut node, &attr, pos);
                         continue;
                     }
                     _ => {
@@ -1756,11 +1764,11 @@ 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 => {
-                        self.expand_cfg_attr(node, attr, pos);
+                        self.expand_cfg_attr(node, &attr, pos);
                         continue;
                     }
                     _ => visit_clobber(node, |node| {