Allow Early stage to emit errors

compiler/rustc_attr_parsing/src/context.rs

@@ -1,6 +1,5 @@
 use std::cell::RefCell;
 use std::collections::BTreeMap;
-use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 use std::sync::LazyLock;
 
@@ -202,7 +201,11 @@ pub trait Stage: Sized + 'static + Sealed {
 
     fn parsers() -> &'static group_type!(Self);
 
-    fn emit_err<'sess>(sess: &'sess Session, diag: impl for<'x> Diagnostic<'x>) -> ErrorGuaranteed;
+    fn emit_err<'sess>(
+        &self,
+        sess: &'sess Session,
+        diag: impl for<'x> Diagnostic<'x>,
+    ) -> ErrorGuaranteed;
 }
 
 // allow because it's a sealed trait
@@ -214,8 +217,16 @@ impl Stage for Early {
     fn parsers() -> &'static group_type!(Self) {
         &early::ATTRIBUTE_PARSERS
     }
-    fn emit_err<'sess>(sess: &'sess Session, diag: impl for<'x> Diagnostic<'x>) -> ErrorGuaranteed {
-        sess.dcx().create_err(diag).delay_as_bug()
+    fn emit_err<'sess>(
+        &self,
+        sess: &'sess Session,
+        diag: impl for<'x> Diagnostic<'x>,
+    ) -> ErrorGuaranteed {
+        if self.emit_errors {
+            sess.dcx().emit_err(diag)
+        } else {
+            sess.dcx().create_err(diag).delay_as_bug()
+        }
     }
 }
 
@@ -228,20 +239,29 @@ impl Stage for Late {
     fn parsers() -> &'static group_type!(Self) {
         &late::ATTRIBUTE_PARSERS
     }
-    fn emit_err<'sess>(tcx: &'sess Session, diag: impl for<'x> Diagnostic<'x>) -> ErrorGuaranteed {
+    fn emit_err<'sess>(
+        &self,
+        tcx: &'sess Session,
+        diag: impl for<'x> Diagnostic<'x>,
+    ) -> ErrorGuaranteed {
         tcx.dcx().emit_err(diag)
     }
 }
 
 /// used when parsing attributes for miscellaneous things *before* ast lowering
-pub struct Early;
+pub struct Early {
+    /// Whether to emit errors or delay them as a bug
+    /// For most attributes, the attribute will be parsed again in the `Late` stage and in this case the errors should be delayed
+    /// But for some, such as `cfg`, the attribute will be removed before the `Late` stage so errors must be emitted
+    pub emit_errors: bool,
+}
 /// used when parsing attributes during ast lowering
 pub struct Late;
 
 /// Context given to every attribute parser when accepting
 ///
 /// Gives [`AttributeParser`]s enough information to create errors, for example.
-pub(crate) struct AcceptContext<'f, 'sess, S: Stage> {
+pub struct AcceptContext<'f, 'sess, S: Stage> {
     pub(crate) shared: SharedContext<'f, 'sess, S>,
     /// The span of the attribute currently being parsed
     pub(crate) attr_span: Span,
@@ -257,7 +277,7 @@ pub(crate) struct AcceptContext<'f, 'sess, S: Stage> {
 
 impl<'f, 'sess: 'f, S: Stage> SharedContext<'f, 'sess, S> {
     pub(crate) fn emit_err(&self, diag: impl for<'x> Diagnostic<'x>) -> ErrorGuaranteed {
-        S::emit_err(&self.sess, diag)
+        self.stage.emit_err(&self.sess, diag)
     }
 
     /// Emit a lint. This method is somewhat special, since lints emitted during attribute parsing
@@ -472,7 +492,7 @@ impl<'f, 'sess, S: Stage> DerefMut for AcceptContext<'f, 'sess, S> {
 ///
 /// Gives [`AttributeParser`](crate::attributes::AttributeParser)s enough information to create
 /// errors, for example.
-pub(crate) struct SharedContext<'p, 'sess, S: Stage> {
+pub struct SharedContext<'p, 'sess, S: Stage> {
     /// The parse context, gives access to the session and the
     /// diagnostics context.
     pub(crate) cx: &'p mut AttributeParser<'sess, S>,
@@ -540,7 +560,7 @@ pub struct AttributeParser<'sess, S: Stage = Late> {
     pub(crate) tools: Vec<Symbol>,
     features: Option<&'sess Features>,
     sess: &'sess Session,
-    stage: PhantomData<S>,
+    stage: S,
 
     /// *Only* parse attributes with this symbol.
     ///
@@ -569,13 +589,14 @@ impl<'sess> AttributeParser<'sess, Early> {
         sym: Symbol,
         target_span: Span,
         target_node_id: NodeId,
+        features: Option<&'sess Features>,
     ) -> Option<Attribute> {
         let mut p = Self {
-            features: None,
+            features,
             tools: Vec::new(),
             parse_only: Some(sym),
             sess,
-            stage: PhantomData,
+            stage: Early { emit_errors: false },
         };
         let mut parsed = p.parse_attribute_list(
             attrs,
@@ -591,11 +612,55 @@ impl<'sess> AttributeParser<'sess, Early> {
 
         parsed.pop()
     }
+
+    pub fn parse_single<T>(
+        sess: &'sess Session,
+        attr: &ast::Attribute,
+        target_span: Span,
+        target_node_id: NodeId,
+        features: Option<&'sess Features>,
+        emit_errors: bool,
+        parse_fn: fn(cx: &mut AcceptContext<'_, '_, Early>, item: &ArgParser<'_>) -> T,
+        template: &AttributeTemplate,
+    ) -> T {
+        let mut parser = Self {
+            features,
+            tools: Vec::new(),
+            parse_only: None,
+            sess,
+            stage: Early { emit_errors },
+        };
+        let ast::AttrKind::Normal(normal_attr) = &attr.kind else {
+            panic!("parse_single called on a doc attr")
+        };
+        let meta_parser = MetaItemParser::from_attr(normal_attr, parser.dcx());
+        let path = meta_parser.path();
+        let args = meta_parser.args();
+        let mut cx: AcceptContext<'_, 'sess, Early> = AcceptContext {
+            shared: SharedContext {
+                cx: &mut parser,
+                target_span,
+                target_id: target_node_id,
+                emit_lint: &mut |_lint| {
+                    panic!("can't emit lints here for now (nothing uses this atm)");
+                },
+            },
+            attr_span: attr.span,
+            template,
+            attr_path: path.get_attribute_path(),
+        };
+        parse_fn(&mut cx, args)
+    }
 }
 
 impl<'sess, S: Stage> AttributeParser<'sess, S> {
-    pub fn new(sess: &'sess Session, features: &'sess Features, tools: Vec<Symbol>) -> Self {
-        Self { features: Some(features), tools, parse_only: None, sess, stage: PhantomData }
+    pub fn new(
+        sess: &'sess Session,
+        features: &'sess Features,
+        tools: Vec<Symbol>,
+        stage: S,
+    ) -> Self {
+        Self { features: Some(features), tools, parse_only: None, sess, stage }
     }
 
     pub(crate) fn sess(&self) -> &'sess Session {
@@ -606,6 +671,10 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
         self.features.expect("features not available at this point in the compiler")
     }
 
+    pub(crate) fn features_option(&self) -> Option<&'sess Features> {
+        self.features
+    }
+
     pub(crate) fn dcx(&self) -> DiagCtxtHandle<'sess> {
         self.sess().dcx()
     }