From ebbcf9f458522e76c5a84e6771e0ef434d6d5c5b Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Wed, 7 Apr 2021 12:45:17 +0100
Subject: Fix inference with conditionally compiled tails

Fixes #8378
---
 crates/hir_def/src/body/lower.rs | 24 +++++++++++++++++-------
 crates/hir_def/src/body/scope.rs |  2 +-
 crates/hir_def/src/expr.rs       |  4 ++--
 3 files changed, 20 insertions(+), 10 deletions(-)

(limited to 'crates/hir_def')

diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index c11da30d2..820d5c17e 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -203,7 +203,7 @@ impl ExprCollector<'_> {
         self.maybe_collect_expr(expr).unwrap_or_else(|| self.missing_expr())
     }
 
-    /// Returns `None` if the expression is `#[cfg]`d out.
+    /// Returns `None` if and only if the expression is `#[cfg]`d out.
     fn maybe_collect_expr(&mut self, expr: ast::Expr) -> Option<ExprId> {
         let syntax_ptr = AstPtr::new(&expr);
         self.check_cfg(&expr)?;
@@ -665,7 +665,7 @@ impl ExprCollector<'_> {
                 if self.check_cfg(&stmt).is_none() {
                     return;
                 }
-
+                let has_semi = stmt.semicolon_token().is_some();
                 // Note that macro could be expended to multiple statements
                 if let Some(ast::Expr::MacroCall(m)) = stmt.expr() {
                     let macro_ptr = AstPtr::new(&m);
@@ -682,18 +682,19 @@ impl ExprCollector<'_> {
                                 statements.statements().for_each(|stmt| this.collect_stmt(stmt));
                                 if let Some(expr) = statements.expr() {
                                     let expr = this.collect_expr(expr);
-                                    this.statements_in_scope.push(Statement::Expr(expr));
+                                    this.statements_in_scope
+                                        .push(Statement::Expr { expr, has_semi });
                                 }
                             }
                             None => {
                                 let expr = this.alloc_expr(Expr::Missing, syntax_ptr.clone());
-                                this.statements_in_scope.push(Statement::Expr(expr));
+                                this.statements_in_scope.push(Statement::Expr { expr, has_semi });
                             }
                         },
                     );
                 } else {
                     let expr = self.collect_expr_opt(stmt.expr());
-                    self.statements_in_scope.push(Statement::Expr(expr));
+                    self.statements_in_scope.push(Statement::Expr { expr, has_semi });
                 }
             }
             ast::Stmt::Item(item) => {
@@ -722,8 +723,17 @@ impl ExprCollector<'_> {
         let prev_statements = std::mem::take(&mut self.statements_in_scope);
 
         block.statements().for_each(|s| self.collect_stmt(s));
-
-        let tail = block.tail_expr().map(|e| self.collect_expr(e));
+        block.tail_expr().and_then(|e| {
+            let expr = self.maybe_collect_expr(e)?;
+            Some(self.statements_in_scope.push(Statement::Expr { expr, has_semi: false }))
+        });
+
+        let mut tail = None;
+        if let Some(Statement::Expr { expr, has_semi: false }) = self.statements_in_scope.last() {
+            tail = Some(*expr);
+            self.statements_in_scope.pop();
+        }
+        let tail = tail;
         let statements = std::mem::replace(&mut self.statements_in_scope, prev_statements);
         let syntax_node_ptr = AstPtr::new(&block.into());
         let expr_id = self.alloc_expr(
diff --git a/crates/hir_def/src/body/scope.rs b/crates/hir_def/src/body/scope.rs
index bd7005ca6..6764de3a7 100644
--- a/crates/hir_def/src/body/scope.rs
+++ b/crates/hir_def/src/body/scope.rs
@@ -157,7 +157,7 @@ fn compute_block_scopes(
                 scope = scopes.new_scope(scope);
                 scopes.add_bindings(body, scope, *pat);
             }
-            Statement::Expr(expr) => {
+            Statement::Expr { expr, .. } => {
                 scopes.set_scope(*expr, scope);
                 compute_expr_scopes(*expr, body, scopes, scope);
             }
diff --git a/crates/hir_def/src/expr.rs b/crates/hir_def/src/expr.rs
index b4ad984bd..0c3b41080 100644
--- a/crates/hir_def/src/expr.rs
+++ b/crates/hir_def/src/expr.rs
@@ -242,7 +242,7 @@ pub struct RecordLitField {
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub enum Statement {
     Let { pat: PatId, type_ref: Option<Interned<TypeRef>>, initializer: Option<ExprId> },
-    Expr(ExprId),
+    Expr { expr: ExprId, has_semi: bool },
 }
 
 impl Expr {
@@ -265,7 +265,7 @@ impl Expr {
                                 f(*expr);
                             }
                         }
-                        Statement::Expr(e) => f(*e),
+                        Statement::Expr { expr: expression, .. } => f(*expression),
                     }
                 }
                 if let Some(expr) = tail {
-- 
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