Remove the non-assigning form of unpack!

This kind of unpacking can be expressed as an ordinary method on
`BlockAnd<()>`.

Author: Zalathar

compiler/rustc_mir_build/src/build/block.rs

@@ -282,7 +282,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         )
                     } else {
                         let scope = (*init_scope, source_info);
-                        unpack!(this.in_scope(scope, *lint_level, |this| {
+                        this.in_scope(scope, *lint_level, |this| {
                             this.declare_bindings(
                                 visibility_scope,
                                 remainder_span,
@@ -291,7 +291,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                 None,
                             );
                             block.unit()
-                        }));
+                        })
+                        .unpack_discard();
 
                         debug!("ast_block_stmts: pattern={:?}", pattern);
                         this.visit_primary_bindings(

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -486,7 +486,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 block.and(Rvalue::Aggregate(result, operands))
             }
             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
-                block = unpack!(this.stmt_expr(block, expr_id, None));
+                block = this.stmt_expr(block, expr_id, None).unpack_block();
                 block.and(Rvalue::Use(Operand::Constant(Box::new(ConstOperand {
                     span: expr_span,
                     user_ty: None,

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -82,13 +82,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         // Lower the condition, and have it branch into `then` and `else` blocks.
                         let (then_block, else_block) =
                             this.in_if_then_scope(condition_scope, then_span, |this| {
-                                let then_blk = unpack!(this.then_else_break(
-                                    block,
-                                    cond,
-                                    Some(condition_scope), // Temp scope
-                                    source_info,
-                                    DeclareLetBindings::Yes, // Declare `let` bindings normally
-                                ));
+                                let then_blk = this
+                                    .then_else_break(
+                                        block,
+                                        cond,
+                                        Some(condition_scope), // Temp scope
+                                        source_info,
+                                        DeclareLetBindings::Yes, // Declare `let` bindings normally
+                                    )
+                                    .unpack_block();
 
                                 // Lower the `then` arm into its block.
                                 this.expr_into_dest(destination, then_blk, then)
@@ -187,7 +189,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         const_: Const::from_bool(this.tcx, constant),
                     },
                 );
-                let mut rhs_block = unpack!(this.expr_into_dest(destination, continuation, rhs));
+                let mut rhs_block =
+                    this.expr_into_dest(destination, continuation, rhs).unpack_block();
                 // Instrument the lowered RHS's value for condition coverage.
                 // (Does nothing if condition coverage is not enabled.)
                 this.visit_coverage_standalone_condition(rhs, destination, &mut rhs_block);
@@ -230,7 +233,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     // introduce a unit temporary as the destination for the loop body.
                     let tmp = this.get_unit_temp();
                     // Execute the body, branching back to the test.
-                    let body_block_end = unpack!(this.expr_into_dest(tmp, body_block, body));
+                    let body_block_end = this.expr_into_dest(tmp, body_block, body).unpack_block();
                     this.cfg.goto(body_block_end, source_info, loop_block);
 
                     // Loops are only exited by `break` expressions.
@@ -462,7 +465,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             targets.push(target);
 
                             let tmp = this.get_unit_temp();
-                            let target = unpack!(this.ast_block(tmp, target, block, source_info));
+                            let target =
+                                this.ast_block(tmp, target, block, source_info).unpack_block();
                             this.cfg.terminate(
                                 target,
                                 source_info,

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -121,8 +121,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         match expr.kind {
             ExprKind::LogicalOp { op: op @ LogicalOp::And, lhs, rhs } => {
                 this.visit_coverage_branch_operation(op, expr_span);
-                let lhs_then_block = unpack!(this.then_else_break_inner(block, lhs, args));
-                let rhs_then_block = unpack!(this.then_else_break_inner(lhs_then_block, rhs, args));
+                let lhs_then_block = this.then_else_break_inner(block, lhs, args).unpack_block();
+                let rhs_then_block =
+                    this.then_else_break_inner(lhs_then_block, rhs, args).unpack_block();
                 rhs_then_block.unit()
             }
             ExprKind::LogicalOp { op: op @ LogicalOp::Or, lhs, rhs } => {
@@ -139,14 +140,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             },
                         )
                     });
-                let rhs_success_block = unpack!(this.then_else_break_inner(
-                    failure_block,
-                    rhs,
-                    ThenElseArgs {
-                        declare_let_bindings: DeclareLetBindings::LetNotPermitted,
-                        ..args
-                    },
-                ));
+                let rhs_success_block = this
+                    .then_else_break_inner(
+                        failure_block,
+                        rhs,
+                        ThenElseArgs {
+                            declare_let_bindings: DeclareLetBindings::LetNotPermitted,
+                            ..args
+                        },
+                    )
+                    .unpack_block();
 
                 // Make the LHS and RHS success arms converge to a common block.
                 // (We can't just make LHS goto RHS, because `rhs_success_block`
@@ -515,7 +518,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             let block = &self.cfg.basic_blocks[arm_block.0];
             let last_location = block.statements.last().map(|s| s.source_info);
 
-            self.cfg.goto(unpack!(arm_block), last_location.unwrap_or(end_brace), end_block);
+            self.cfg.goto(arm_block.unpack_block(), last_location.unwrap_or(end_brace), end_block);
         }
 
         self.source_scope = outer_source_info.scope;

compiler/rustc_mir_build/src/build/mod.rs

@@ -403,6 +403,21 @@ enum NeedsTemporary {
 #[must_use = "if you don't use one of these results, you're leaving a dangling edge"]
 struct BlockAnd<T>(BasicBlock, T);
 
+impl BlockAnd<()> {
+    /// Unpacks `BlockAnd<()>` into a [`BasicBlock`].
+    #[must_use]
+    fn unpack_block(self) -> BasicBlock {
+        let Self(block, ()) = self;
+        block
+    }
+
+    /// Explicitly discards a [`BlockAnd<()>`] value.
+    ///
+    /// This is similar to writing `let _ = ...`, except that it is also
+    /// (a) postfix, and (b) searchable.
+    fn unpack_discard(self) {}
+}
+
 trait BlockAndExtension {
     fn and<T>(self, v: T) -> BlockAnd<T>;
     fn unit(self) -> BlockAnd<()>;
@@ -426,11 +441,6 @@ macro_rules! unpack {
         $x = b;
         v
     }};
-
-    ($c:expr) => {{
-        let BlockAnd(b, ()) = $c;
-        b
-    }};
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -516,21 +526,24 @@ fn construct_fn<'tcx>(
         region::Scope { id: body.id().hir_id.local_id, data: region::ScopeData::Arguments };
     let source_info = builder.source_info(span);
     let call_site_s = (call_site_scope, source_info);
-    unpack!(builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {
-        let arg_scope_s = (arg_scope, source_info);
-        // Attribute epilogue to function's closing brace
-        let fn_end = span_with_body.shrink_to_hi();
-        let return_block =
-            unpack!(builder.in_breakable_scope(None, Place::return_place(), fn_end, |builder| {
-                Some(builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
-                    builder.args_and_body(START_BLOCK, arguments, arg_scope, expr)
-                }))
-            }));
-        let source_info = builder.source_info(fn_end);
-        builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
-        builder.build_drop_trees();
-        return_block.unit()
-    }));
+    builder
+        .in_scope(call_site_s, LintLevel::Inherited, |builder| {
+            let arg_scope_s = (arg_scope, source_info);
+            // Attribute epilogue to function's closing brace
+            let fn_end = span_with_body.shrink_to_hi();
+            let return_block = builder
+                .in_breakable_scope(None, Place::return_place(), fn_end, |builder| {
+                    Some(builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
+                        builder.args_and_body(START_BLOCK, arguments, arg_scope, expr)
+                    }))
+                })
+                .unpack_block();
+            let source_info = builder.source_info(fn_end);
+            builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
+            builder.build_drop_trees();
+            return_block.unit()
+        })
+        .unpack_discard();
 
     let mut body = builder.finish();
 

compiler/rustc_mir_build/src/build/scope.rs

@@ -510,12 +510,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let target = self.cfg.start_new_block();
                 let source_info = self.source_info(span);
                 self.cfg.terminate(
-                    unpack!(normal_block),
+                    normal_block.unpack_block(),
                     source_info,
                     TerminatorKind::Goto { target },
                 );
                 self.cfg.terminate(
-                    unpack!(exit_block),
+                    exit_block.unpack_block(),
                     source_info,
                     TerminatorKind::Goto { target },
                 );
@@ -552,14 +552,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let scope = IfThenScope { region_scope, else_drops: DropTree::new() };
         let previous_scope = mem::replace(&mut self.scopes.if_then_scope, Some(scope));
 
-        let then_block = unpack!(f(self));
+        let then_block = f(self).unpack_block();
 
         let if_then_scope = mem::replace(&mut self.scopes.if_then_scope, previous_scope).unwrap();
         assert!(if_then_scope.region_scope == region_scope);
 
-        let else_block = self
-            .build_exit_tree(if_then_scope.else_drops, region_scope, span, None)
-            .map_or_else(|| self.cfg.start_new_block(), |else_block_and| unpack!(else_block_and));
+        let else_block =
+            self.build_exit_tree(if_then_scope.else_drops, region_scope, span, None).map_or_else(
+                || self.cfg.start_new_block(),
+                |else_block_and| else_block_and.unpack_block(),
+            );
 
         (then_block, else_block)
     }
@@ -753,15 +755,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let unwind_to = if needs_cleanup { self.diverge_cleanup() } else { DropIdx::MAX };
 
         let scope = self.scopes.scopes.last().expect("leave_top_scope called with no scopes");
-        unpack!(build_scope_drops(
+        build_scope_drops(
             &mut self.cfg,
             &mut self.scopes.unwind_drops,
             scope,
             block,
             unwind_to,
             is_coroutine && needs_cleanup,
             self.arg_count,
-        ))
+        )
+        .unpack_block()
     }
 
     /// Possibly creates a new source scope if `current_root` and `parent_root`