For diagnostics, set spans of drops of temps to be that of the statem…

…ent's terminating semicolon.
rust-lang · bors · Nov 15, 2018 · Aug 11, 2018 · Aug 11, 2018 · Aug 17, 2018
commit ece4f472c923d72faf50efaaba60a8f51c143bec
diff --git a/src/librustc_mir/build/block.rs b/src/librustc_mir/build/block.rs
@@ -90,7 +90,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
         let source_info = this.source_info(span);
         for stmt in stmts {
-            let Stmt { kind, opt_destruction_scope } = this.hir.mirror(stmt);
+            let Stmt { kind, opt_destruction_scope, span: stmt_span } = this.hir.mirror(stmt);
             match kind {
                 StmtKind::Expr { scope, expr } => {
                     this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
@@ -99,7 +99,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                             let si = (scope, source_info);
                             this.in_scope(si, LintLevel::Inherited, block, |this| {
                                 let expr = this.hir.mirror(expr);
-                                this.stmt_expr(block, expr)
+                                this.stmt_expr(block, expr, Some(stmt_span))
                             })
                         }));
                 }

diff --git a/src/librustc_mir/build/expr/as_rvalue.rs b/src/librustc_mir/build/expr/as_rvalue.rs
@@ -351,7 +351,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 block.and(Rvalue::Aggregate(adt, fields))
             }
             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
-                block = unpack!(this.stmt_expr(block, expr));
+                block = unpack!(this.stmt_expr(block, expr, None));
                 block.and(this.unit_rvalue())
             }
             ExprKind::Yield { value } => {

diff --git a/src/librustc_mir/build/expr/into.rs b/src/librustc_mir/build/expr/into.rs
@@ -351,7 +351,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             | ExprKind::Break { .. }
             | ExprKind::InlineAsm { .. }
             | ExprKind::Return { .. } => {
-                unpack!(block = this.stmt_expr(block, expr));
+                unpack!(block = this.stmt_expr(block, expr, None));
                 this.cfg.push_assign_unit(block, source_info, destination);
                 block.unit()
             }

diff --git a/src/librustc_mir/build/expr/stmt.rs b/src/librustc_mir/build/expr/stmt.rs
@@ -14,7 +14,18 @@ use hair::*;
 use rustc::mir::*;
 
 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
-    pub fn stmt_expr(&mut self, mut block: BasicBlock, expr: Expr<'tcx>) -> BlockAnd<()> {
+    /// Builds a block of MIR statements to evaluate the HAIR `expr`.
+    /// If the original expression was an AST statement,
+    /// (e.g. `some().code(&here());`) then `opt_stmt_span` is the
+    /// span of that statement (including its semicolon, if any).
+    /// Diagnostics use this span (which may be larger than that of
+    /// `expr`) to identify when statement temporaries are dropped.
+    pub fn stmt_expr(&mut self,
+                     mut block: BasicBlock,
+                     expr: Expr<'tcx>,
+                     opt_stmt_span: Option<StatementSpan>)
+                     -> BlockAnd<()>
+    {
         let this = self;
         let expr_span = expr.span;
         let source_info = this.source_info(expr.span);
@@ -29,7 +40,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             } => {
                 let value = this.hir.mirror(value);
                 this.in_scope((region_scope, source_info), lint_level, block, |this| {
-                    this.stmt_expr(block, value)
+                    this.stmt_expr(block, value, opt_stmt_span)
                 })
             }
             ExprKind::Assign { lhs, rhs } => {
@@ -192,7 +203,15 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 let expr_ty = expr.ty;
                 let temp = this.temp(expr.ty.clone(), expr_span);
                 unpack!(block = this.into(&temp, block, expr));
-                unpack!(block = this.build_drop(block, expr_span, temp, expr_ty));
+
+                // Attribute drops of the statement's temps to the
+                // semicolon at the statement's end.
+                let drop_point = this.hir.tcx().sess.source_map().end_point(match opt_stmt_span {
+                    None => expr_span,
+                    Some(StatementSpan(span)) => span,
+                });
+
+                unpack!(block = this.build_drop(block, drop_point, temp, expr_ty));
                 block.unit()
             }
         }

diff --git a/src/librustc_mir/hair/cx/block.rs b/src/librustc_mir/hair/cx/block.rs
@@ -57,6 +57,7 @@ fn mirror_stmts<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
     for (index, stmt) in stmts.iter().enumerate() {
         let hir_id = cx.tcx.hir.node_to_hir_id(stmt.node.id());
         let opt_dxn_ext = cx.region_scope_tree.opt_destruction_scope(hir_id.local_id);
+        let stmt_span = StatementSpan(cx.tcx.hir.span(stmt.node.id()));
         match stmt.node {
             hir::StmtKind::Expr(ref expr, _) |
             hir::StmtKind::Semi(ref expr, _) => {
@@ -69,6 +70,7 @@ fn mirror_stmts<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                         expr: expr.to_ref(),
                     },
                     opt_destruction_scope: opt_dxn_ext,
+                    span: stmt_span,
                 })))
             }
             hir::StmtKind::Decl(ref decl, _) => {
@@ -111,6 +113,7 @@ fn mirror_stmts<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                                 lint_level: cx.lint_level_of(local.id),
                             },
                             opt_destruction_scope: opt_dxn_ext,
+                            span: stmt_span,
                         })));
                     }
                 }

diff --git a/src/librustc_mir/hair/mod.rs b/src/librustc_mir/hair/mod.rs
@@ -71,10 +71,14 @@ pub enum StmtRef<'tcx> {
     Mirror(Box<Stmt<'tcx>>),
 }
 
+#[derive(Clone, Debug)]
+pub struct StatementSpan(pub Span);
+
 #[derive(Clone, Debug)]
 pub struct Stmt<'tcx> {
     pub kind: StmtKind<'tcx>,
     pub opt_destruction_scope: Option<region::Scope>,
+    pub span: StatementSpan,
 }
 
 #[derive(Clone, Debug)]