Correctly resolve variables and labels from before macro definition i…

…n macro expansion

E.g.:
```rust
let v;
macro_rules! m { () => { v }; }
```

This was an existing bug, but it was less severe because unless the variable was shadowed it would be correctly resolved. With hygiene however, without this fix the variable is never resolved.

crates/hir-def/src/body.rs

@@ -35,7 +35,7 @@ use crate::{
 
 /// A wrapper around [`span::SyntaxContextId`] that is intended only for comparisons.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct HygieneId(span::SyntaxContextId);
+pub struct HygieneId(pub(crate) span::SyntaxContextId);
 
 impl HygieneId {
     pub const ROOT: Self = Self(span::SyntaxContextId::ROOT);
@@ -44,7 +44,7 @@ impl HygieneId {
         Self(ctx)
     }
 
-    fn is_root(self) -> bool {
+    pub(crate) fn is_root(self) -> bool {
         self.0.is_root()
     }
 }
@@ -420,7 +420,7 @@ impl Body {
                             self.walk_exprs_in_pat(*pat, &mut f);
                         }
                         Statement::Expr { expr: expression, .. } => f(*expression),
-                        Statement::Item => (),
+                        Statement::Item(_) => (),
                     }
                 }
                 if let &Some(expr) = tail {

crates/hir-def/src/body/lower.rs

@@ -10,7 +10,7 @@ use either::Either;
 use hir_expand::{
     name::{AsName, Name},
     span_map::{ExpansionSpanMap, SpanMap},
-    InFile,
+    InFile, MacroDefId,
 };
 use intern::{sym, Interned, Symbol};
 use rustc_hash::FxHashMap;
@@ -39,16 +39,16 @@ use crate::{
             FormatPlaceholder, FormatSign, FormatTrait,
         },
         Array, Binding, BindingAnnotation, BindingId, BindingProblems, CaptureBy, ClosureKind,
-        Expr, ExprId, Label, LabelId, Literal, LiteralOrConst, MatchArm, Movability, OffsetOf, Pat,
-        PatId, RecordFieldPat, RecordLitField, Statement,
+        Expr, ExprId, Item, Label, LabelId, Literal, LiteralOrConst, MatchArm, Movability,
+        OffsetOf, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
     },
     item_scope::BuiltinShadowMode,
     lang_item::LangItem,
     lower::LowerCtx,
     nameres::{DefMap, MacroSubNs},
     path::{GenericArgs, Path},
     type_ref::{Mutability, Rawness, TypeRef},
-    AdtId, BlockId, BlockLoc, ConstBlockLoc, DefWithBodyId, ModuleDefId, UnresolvedMacro,
+    AdtId, BlockId, BlockLoc, ConstBlockLoc, DefWithBodyId, MacroId, ModuleDefId, UnresolvedMacro,
 };
 
 type FxIndexSet<K> = indexmap::IndexSet<K, std::hash::BuildHasherDefault<rustc_hash::FxHasher>>;
@@ -88,6 +88,7 @@ pub(super) fn lower(
         current_binding_owner: None,
         awaitable_context: None,
         current_span_map: span_map,
+        current_block_legacy_macro_defs_count: FxHashMap::default(),
     }
     .collect(params, body, is_async_fn)
 }
@@ -104,6 +105,10 @@ struct ExprCollector<'a> {
 
     is_lowering_coroutine: bool,
 
+    /// Legacy (`macro_rules!`) macros can have multiple definitions and shadow each other,
+    /// and we need to find the current definition. So we track the number of definitions we saw.
+    current_block_legacy_macro_defs_count: FxHashMap<Name, usize>,
+
     current_span_map: Option<Arc<ExpansionSpanMap>>,
 
     current_try_block_label: Option<LabelId>,
@@ -124,31 +129,27 @@ struct ExprCollector<'a> {
 #[derive(Clone, Debug)]
 struct LabelRib {
     kind: RibKind,
-    // Once we handle macro hygiene this will need to be a map
-    label: Option<(Name, LabelId, HygieneId)>,
 }
 
 impl LabelRib {
     fn new(kind: RibKind) -> Self {
-        LabelRib { kind, label: None }
-    }
-    fn new_normal(label: (Name, LabelId, HygieneId)) -> Self {
-        LabelRib { kind: RibKind::Normal, label: Some(label) }
+        LabelRib { kind }
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 enum RibKind {
-    Normal,
+    Normal(Name, LabelId, HygieneId),
     Closure,
     Constant,
+    MacroDef(Box<MacroDefId>),
 }
 
 impl RibKind {
     /// This rib forbids referring to labels defined in upwards ribs.
-    fn is_label_barrier(self) -> bool {
+    fn is_label_barrier(&self) -> bool {
         match self {
-            RibKind::Normal => false,
+            RibKind::Normal(..) | RibKind::MacroDef(_) => false,
             RibKind::Closure | RibKind::Constant => true,
         }
     }
@@ -1350,10 +1351,46 @@ impl ExprCollector<'_> {
                     statements.push(Statement::Expr { expr, has_semi });
                 }
             }
-            ast::Stmt::Item(_item) => statements.push(Statement::Item),
+            ast::Stmt::Item(ast::Item::MacroDef(macro_)) => {
+                let Some(name) = macro_.name() else {
+                    statements.push(Statement::Item(Item::Other));
+                    return;
+                };
+                let name = name.as_name();
+                let macro_id = self.def_map.modules[DefMap::ROOT].scope.get(&name).take_macros();
+                self.collect_macro_def(statements, macro_id);
+            }
+            ast::Stmt::Item(ast::Item::MacroRules(macro_)) => {
+                let Some(name) = macro_.name() else {
+                    statements.push(Statement::Item(Item::Other));
+                    return;
+                };
+                let name = name.as_name();
+                let macro_defs_count =
+                    self.current_block_legacy_macro_defs_count.entry(name.clone()).or_insert(0);
+                let macro_id = self.def_map.modules[DefMap::ROOT]
+                    .scope
+                    .get_legacy_macro(&name)
+                    .and_then(|it| it.get(*macro_defs_count))
+                    .copied();
+                *macro_defs_count += 1;
+                self.collect_macro_def(statements, macro_id);
+            }
+            ast::Stmt::Item(_item) => statements.push(Statement::Item(Item::Other)),
         }
     }
 
+    fn collect_macro_def(&mut self, statements: &mut Vec<Statement>, macro_id: Option<MacroId>) {
+        let Some(macro_id) = macro_id else {
+            never!("def map should have macro definition, but it doesn't");
+            statements.push(Statement::Item(Item::Other));
+            return;
+        };
+        let macro_id = self.db.macro_def(macro_id);
+        statements.push(Statement::Item(Item::MacroDef(Box::new(macro_id))));
+        self.label_ribs.push(LabelRib::new(RibKind::MacroDef(Box::new(macro_id))));
+    }
+
     fn collect_block(&mut self, block: ast::BlockExpr) -> ExprId {
         self.collect_block_(block, |id, statements, tail| Expr::Block {
             id,
@@ -1399,6 +1436,7 @@ impl ExprCollector<'_> {
             };
         let prev_def_map = mem::replace(&mut self.def_map, def_map);
         let prev_local_module = mem::replace(&mut self.expander.module, module);
+        let prev_legacy_macros_count = mem::take(&mut self.current_block_legacy_macro_defs_count);
 
         let mut statements = Vec::new();
         block.statements().for_each(|s| self.collect_stmt(&mut statements, s));
@@ -1421,6 +1459,7 @@ impl ExprCollector<'_> {
 
         self.def_map = prev_def_map;
         self.expander.module = prev_local_module;
+        self.current_block_legacy_macro_defs_count = prev_legacy_macros_count;
         expr_id
     }
 
@@ -1780,21 +1819,51 @@ impl ExprCollector<'_> {
         lifetime: Option<ast::Lifetime>,
     ) -> Result<Option<LabelId>, BodyDiagnostic> {
         let Some(lifetime) = lifetime else { return Ok(None) };
-        let hygiene = self.hygiene_id_for(lifetime.syntax().text_range().start());
+        let (mut hygiene_id, mut hygiene_info) = match &self.current_span_map {
+            None => (HygieneId::ROOT, None),
+            Some(span_map) => {
+                let span = span_map.span_at(lifetime.syntax().text_range().start());
+                let ctx = self.db.lookup_intern_syntax_context(span.ctx);
+                let hygiene_id = HygieneId::new(ctx.opaque_and_semitransparent);
+                let hygiene_info = ctx.outer_expn.map(|expansion| {
+                    let expansion = self.db.lookup_intern_macro_call(expansion);
+                    (ctx.parent, expansion.def)
+                });
+                (hygiene_id, hygiene_info)
+            }
+        };
         let name = Name::new_lifetime(&lifetime);
 
         for (rib_idx, rib) in self.label_ribs.iter().enumerate().rev() {
-            if let Some((label_name, id, label_hygiene)) = &rib.label {
-                if *label_name == name && *label_hygiene == hygiene {
-                    return if self.is_label_valid_from_rib(rib_idx) {
-                        Ok(Some(*id))
-                    } else {
-                        Err(BodyDiagnostic::UnreachableLabel {
-                            name,
-                            node: self.expander.in_file(AstPtr::new(&lifetime)),
-                        })
-                    };
+            match &rib.kind {
+                RibKind::Normal(label_name, id, label_hygiene) => {
+                    if *label_name == name && *label_hygiene == hygiene_id {
+                        return if self.is_label_valid_from_rib(rib_idx) {
+                            Ok(Some(*id))
+                        } else {
+                            Err(BodyDiagnostic::UnreachableLabel {
+                                name,
+                                node: self.expander.in_file(AstPtr::new(&lifetime)),
+                            })
+                        };
+                    }
+                }
+                RibKind::MacroDef(macro_id) => {
+                    if let Some((parent_ctx, label_macro_id)) = hygiene_info {
+                        if label_macro_id == **macro_id {
+                            // A macro is allowed to refer to labels from before its declaration.
+                            // Therefore, if we got to the rib of its declaration, give up its hygiene
+                            // and use its parent expansion.
+                            let parent_ctx = self.db.lookup_intern_syntax_context(parent_ctx);
+                            hygiene_id = HygieneId::new(parent_ctx.opaque_and_semitransparent);
+                            hygiene_info = parent_ctx.outer_expn.map(|expansion| {
+                                let expansion = self.db.lookup_intern_macro_call(expansion);
+                                (parent_ctx.parent, expansion.def)
+                            });
+                        }
+                    }
                 }
+                _ => {}
             }
         }
 
@@ -1808,10 +1877,17 @@ impl ExprCollector<'_> {
         !self.label_ribs[rib_index + 1..].iter().any(|rib| rib.kind.is_label_barrier())
     }
 
+    fn pop_label_rib(&mut self) {
+        // We need to pop all macro defs, plus one rib.
+        while let Some(LabelRib { kind: RibKind::MacroDef(_) }) = self.label_ribs.pop() {
+            // Do nothing.
+        }
+    }
+
     fn with_label_rib<T>(&mut self, kind: RibKind, f: impl FnOnce(&mut Self) -> T) -> T {
         self.label_ribs.push(LabelRib::new(kind));
         let res = f(self);
-        self.label_ribs.pop();
+        self.pop_label_rib();
         res
     }
 
@@ -1821,9 +1897,13 @@ impl ExprCollector<'_> {
         hygiene: HygieneId,
         f: impl FnOnce(&mut Self) -> T,
     ) -> T {
-        self.label_ribs.push(LabelRib::new_normal((self.body[label].name.clone(), label, hygiene)));
+        self.label_ribs.push(LabelRib::new(RibKind::Normal(
+            self.body[label].name.clone(),
+            label,
+            hygiene,
+        )));
         let res = f(self);
-        self.label_ribs.pop();
+        self.pop_label_rib();
         res
     }
 

crates/hir-def/src/body/pretty.rs

@@ -753,7 +753,7 @@ impl Printer<'_> {
                 }
                 wln!(self);
             }
-            Statement::Item => (),
+            Statement::Item(_) => (),
         }
     }
 

crates/hir-def/src/body/scope.rs

@@ -1,12 +1,12 @@
 //! Name resolution for expressions.
-use hir_expand::name::Name;
+use hir_expand::{name::Name, MacroDefId};
 use la_arena::{Arena, ArenaMap, Idx, IdxRange, RawIdx};
 use triomphe::Arc;
 
 use crate::{
     body::{Body, HygieneId},
     db::DefDatabase,
-    hir::{Binding, BindingId, Expr, ExprId, LabelId, Pat, PatId, Statement},
+    hir::{Binding, BindingId, Expr, ExprId, Item, LabelId, Pat, PatId, Statement},
     BlockId, ConstBlockId, DefWithBodyId,
 };
 
@@ -45,6 +45,8 @@ pub struct ScopeData {
     parent: Option<ScopeId>,
     block: Option<BlockId>,
     label: Option<(LabelId, Name)>,
+    // FIXME: We can compress this with an enum for this and `label`/`block` if memory usage matters.
+    macro_def: Option<Box<MacroDefId>>,
     entries: IdxRange<ScopeEntry>,
 }
 
@@ -67,6 +69,11 @@ impl ExprScopes {
         self.scopes[scope].block
     }
 
+    /// If `scope` refers to a macro def scope, returns the corresponding `MacroId`.
+    pub fn macro_def(&self, scope: ScopeId) -> Option<&Box<MacroDefId>> {
+        self.scopes[scope].macro_def.as_ref()
+    }
+
     /// If `scope` refers to a labeled expression scope, returns the corresponding `Label`.
     pub fn label(&self, scope: ScopeId) -> Option<(LabelId, Name)> {
         self.scopes[scope].label.clone()
@@ -119,6 +126,7 @@ impl ExprScopes {
             parent: None,
             block: None,
             label: None,
+            macro_def: None,
             entries: empty_entries(self.scope_entries.len()),
         })
     }
@@ -128,6 +136,7 @@ impl ExprScopes {
             parent: Some(parent),
             block: None,
             label: None,
+            macro_def: None,
             entries: empty_entries(self.scope_entries.len()),
         })
     }
@@ -137,6 +146,7 @@ impl ExprScopes {
             parent: Some(parent),
             block: None,
             label,
+            macro_def: None,
             entries: empty_entries(self.scope_entries.len()),
         })
     }
@@ -151,6 +161,17 @@ impl ExprScopes {
             parent: Some(parent),
             block,
             label,
+            macro_def: None,
+            entries: empty_entries(self.scope_entries.len()),
+        })
+    }
+
+    fn new_macro_def_scope(&mut self, parent: ScopeId, macro_id: Box<MacroDefId>) -> ScopeId {
+        self.scopes.alloc(ScopeData {
+            parent: Some(parent),
+            block: None,
+            label: None,
+            macro_def: Some(macro_id),
             entries: empty_entries(self.scope_entries.len()),
         })
     }
@@ -217,7 +238,10 @@ fn compute_block_scopes(
             Statement::Expr { expr, .. } => {
                 compute_expr_scopes(*expr, body, scopes, scope, resolve_const_block);
             }
-            Statement::Item => (),
+            Statement::Item(Item::MacroDef(macro_id)) => {
+                *scope = scopes.new_macro_def_scope(*scope, macro_id.clone());
+            }
+            Statement::Item(Item::Other) => (),
         }
     }
     if let Some(expr) = tail {

crates/hir-def/src/hir.rs

@@ -17,7 +17,7 @@ pub mod type_ref;
 
 use std::fmt;
 
-use hir_expand::name::Name;
+use hir_expand::{name::Name, MacroDefId};
 use intern::{Interned, Symbol};
 use la_arena::{Idx, RawIdx};
 use rustc_apfloat::ieee::{Half as f16, Quad as f128};
@@ -492,9 +492,13 @@ pub enum Statement {
         expr: ExprId,
         has_semi: bool,
     },
-    // At the moment, we only use this to figure out if a return expression
-    // is really the last statement of a block. See #16566
-    Item,
+    Item(Item),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Item {
+    MacroDef(Box<MacroDefId>),
+    Other,
 }
 
 /// Explicit binding annotations given in the HIR for a binding. Note