3 files changed, 141 insertions, 14 deletions

diff --git a/crates/hir_def/src/body/diagnostics.rs b/crates/hir_def/src/body/diagnostics.rs
new file mode 100644
index 000000000..cfa47d189
--- /dev/null
+++ b/crates/hir_def/src/body/diagnostics.rs
@@ -0,0 +1,20 @@
+//! Diagnostics emitted during body lowering.
+
+use hir_expand::diagnostics::DiagnosticSink;
+
+use crate::diagnostics::InactiveCode;
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum BodyDiagnostic {
+    InactiveCode(InactiveCode),
+}
+
+impl BodyDiagnostic {
+    pub fn add_to(&self, sink: &mut DiagnosticSink<'_>) {
+        match self {
+            BodyDiagnostic::InactiveCode(diag) => {
+                sink.push(diag.clone());
+            }
+        }
+    }
+}
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index 01e72690a..ddc267b83 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -16,7 +16,7 @@ use syntax::{
         self, ArgListOwner, ArrayExprKind, AstChildren, LiteralKind, LoopBodyOwner, NameOwner,
         SlicePatComponents,
     },
-    AstNode, AstPtr,
+    AstNode, AstPtr, SyntaxNodePtr,
 };
 use test_utils::mark;
 
@@ -25,6 +25,7 @@ use crate::{
     body::{Body, BodySourceMap, Expander, PatPtr, SyntheticSyntax},
     builtin_type::{BuiltinFloat, BuiltinInt},
     db::DefDatabase,
+    diagnostics::InactiveCode,
     expr::{
         dummy_expr_id, ArithOp, Array, BinaryOp, BindingAnnotation, CmpOp, Expr, ExprId, Literal,
         LogicOp, MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
@@ -37,7 +38,7 @@ use crate::{
     StaticLoc, StructLoc, TraitLoc, TypeAliasLoc, UnionLoc,
 };
 
-use super::{ExprSource, PatSource};
+use super::{diagnostics::BodyDiagnostic, ExprSource, PatSource};
 
 pub(crate) struct LowerCtx {
     hygiene: Hygiene,
@@ -176,7 +177,7 @@ impl ExprCollector<'_> {
 
     fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {
         let syntax_ptr = AstPtr::new(&expr);
-        if !self.expander.is_cfg_enabled(&expr) {
+        if self.check_cfg(&expr).is_none() {
             return self.missing_expr();
         }
 
@@ -354,13 +355,15 @@ impl ExprCollector<'_> {
                 let arms = if let Some(match_arm_list) = e.match_arm_list() {
                     match_arm_list
                         .arms()
-                        .map(|arm| MatchArm {
-                            pat: self.collect_pat_opt(arm.pat()),
-                            expr: self.collect_expr_opt(arm.expr()),
-                            guard: arm
-                                .guard()
-                                .and_then(|guard| guard.expr())
-                                .map(|e| self.collect_expr(e)),
+                        .filter_map(|arm| {
+                            self.check_cfg(&arm).map(|()| MatchArm {
+                                pat: self.collect_pat_opt(arm.pat()),
+                                expr: self.collect_expr_opt(arm.expr()),
+                                guard: arm
+                                    .guard()
+                                    .and_then(|guard| guard.expr())
+                                    .map(|e| self.collect_expr(e)),
+                            })
                         })
                         .collect()
                 } else {
@@ -406,9 +409,8 @@ impl ExprCollector<'_> {
                         .fields()
                         .inspect(|field| field_ptrs.push(AstPtr::new(field)))
                         .filter_map(|field| {
-                            if !self.expander.is_cfg_enabled(&field) {
-                                return None;
-                            }
+                            self.check_cfg(&field)?;
+
                             let name = field.field_name()?.as_name();
 
                             Some(RecordLitField {
@@ -620,15 +622,23 @@ impl ExprCollector<'_> {
             .filter_map(|s| {
                 let stmt = match s {
                     ast::Stmt::LetStmt(stmt) => {
+                        self.check_cfg(&stmt)?;
+
                         let pat = self.collect_pat_opt(stmt.pat());
                         let type_ref = stmt.ty().map(|it| TypeRef::from_ast(&self.ctx(), it));
                         let initializer = stmt.initializer().map(|e| self.collect_expr(e));
                         Statement::Let { pat, type_ref, initializer }
                     }
                     ast::Stmt::ExprStmt(stmt) => {
+                        self.check_cfg(&stmt)?;
+
                         Statement::Expr(self.collect_expr_opt(stmt.expr()))
                     }
-                    ast::Stmt::Item(_) => return None,
+                    ast::Stmt::Item(item) => {
+                        self.check_cfg(&item)?;
+
+                        return None;
+                    }
                 };
                 Some(stmt)
             })
@@ -872,6 +882,28 @@ impl ExprCollector<'_> {
 
         (args, ellipsis)
     }
+
+    /// Returns `None` (and emits diagnostics) when `owner` if `#[cfg]`d out, and `Some(())` when
+    /// not.
+    fn check_cfg(&mut self, owner: &dyn ast::AttrsOwner) -> Option<()> {
+        match self.expander.parse_attrs(owner).cfg() {
+            Some(cfg) => {
+                if self.expander.cfg_options().check(&cfg) != Some(false) {
+                    return Some(());
+                }
+
+                self.source_map.diagnostics.push(BodyDiagnostic::InactiveCode(InactiveCode {
+                    file: self.expander.current_file_id,
+                    node: SyntaxNodePtr::new(owner.syntax()),
+                    cfg,
+                    opts: self.expander.cfg_options().clone(),
+                }));
+
+                None
+            }
+            None => Some(()),
+        }
+    }
 }
 
 impl From<ast::BinOp> for BinaryOp {
diff --git a/crates/hir_def/src/body/tests.rs b/crates/hir_def/src/body/tests.rs
new file mode 100644
index 000000000..f07df5cee
--- /dev/null
+++ b/crates/hir_def/src/body/tests.rs
@@ -0,0 +1,75 @@
+use base_db::{fixture::WithFixture, SourceDatabase};
+use test_utils::mark;
+
+use crate::{test_db::TestDB, ModuleDefId};
+
+use super::*;
+
+fn lower(ra_fixture: &str) -> Arc<Body> {
+    let (db, file_id) = crate::test_db::TestDB::with_single_file(ra_fixture);
+
+    let krate = db.crate_graph().iter().next().unwrap();
+    let def_map = db.crate_def_map(krate);
+    let module = def_map.modules_for_file(file_id).next().unwrap();
+    let module = &def_map[module];
+    let fn_def = match module.scope.declarations().next().unwrap() {
+        ModuleDefId::FunctionId(it) => it,
+        _ => panic!(),
+    };
+
+    db.body(fn_def.into())
+}
+
+fn check_diagnostics(ra_fixture: &str) {
+    let db: TestDB = TestDB::with_files(ra_fixture);
+    db.check_diagnostics();
+}
+
+#[test]
+fn your_stack_belongs_to_me() {
+    mark::check!(your_stack_belongs_to_me);
+    lower(
+        "
+macro_rules! n_nuple {
+    ($e:tt) => ();
+    ($($rest:tt)*) => {{
+        (n_nuple!($($rest)*)None,)
+    }};
+}
+fn main() { n_nuple!(1,2,3); }
+",
+    );
+}
+
+#[test]
+fn cfg_diagnostics() {
+    check_diagnostics(
+        r"
+fn f() {
+    // The three g̶e̶n̶d̶e̶r̶s̶ statements:
+
+    #[cfg(a)] fn f() {}  // Item statement
+  //^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] {}         // Expression statement
+  //^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] let x = 0; // let statement
+  //^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+
+    abc(#[cfg(a)] 0);
+      //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    let x = Struct {
+        #[cfg(a)] f: 0,
+      //^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    };
+    match () {
+        () => (),
+        #[cfg(a)] () => (),
+      //^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    }
+
+    #[cfg(a)] 0          // Trailing expression of block
+  //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+}
+    ",
+    );
+}