Prefer #![feature(bind_by_move_pattern_guards)] over `-Z disable_as…

…t_check_for_mutation_in_guard`

src/librustc/session/config.rs

@@ -1320,8 +1320,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         useful for profiling / PGO."),
     relro_level: Option<RelroLevel> = (None, parse_relro_level, [TRACKED],
         "choose which RELRO level to use"),
-    disable_ast_check_for_mutation_in_guard: bool = (false, parse_bool, [UNTRACKED],
-        "skip AST-based mutation-in-guard check (mir-borrowck provides more precise check)"),
     nll_subminimal_causes: bool = (false, parse_bool, [UNTRACKED],
         "when tracking region error causes, accept subminimal results for faster execution."),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],

src/librustc/ty/context.rs

@@ -1465,11 +1465,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     /// If true, we should use a naive AST walk to determine if match
     /// guard could perform bad mutations (or mutable-borrows).
     pub fn check_for_mutation_in_guard_via_ast_walk(self) -> bool {
-        // If someone passes the `-Z` flag, they're asking for the footgun.
-        if self.sess.opts.debugging_opts.disable_ast_check_for_mutation_in_guard {
-            return false;
-        }
-
         // If someone requests the feature, then be a little more
         // careful and ensure that MIR-borrowck is enabled (which can
         // happen via edition selection, via `feature(nll)`, or via an

src/test/run-pass/issues/issue-24535-allow-mutable-borrow-in-match-guard.rs

@@ -12,12 +12,11 @@
 // This test illustrates that under NLL, we can remove our overly
 // conservative approach for disallowing mutations of match inputs.
 
-// See further discussion on rust-lang/rust#24535 and
-// rust-lang/rfcs#1006.
-
-// compile-flags: -Z disable-ast-check-for-mutation-in-guard
+// See further discussion on rust-lang/rust#24535,
+// rust-lang/rfcs#1006, and rust-lang/rfcs#107
 
 #![feature(nll)]
+#![feature(bind_by_move_pattern_guards)]
 
 fn main() {
     rust_issue_24535();

src/test/ui/issues/issue-27282-reborrow-ref-mut-in-guard.rs

@@ -15,8 +15,8 @@
 // reject it. But I want to make sure that we continue to reject it
 // (under NLL) even when that conservaive check goes away.
 
-// compile-flags: -Z disable-ast-check-for-mutation-in-guard
 
+#![feature(bind_by_move_pattern_guards)]
 #![feature(nll)]
 
 fn main() {

src/test/ui/nll/match-guards-partially-borrow.rs

@@ -5,8 +5,8 @@
 // Test that we don't allow mutating the value being matched on in a way that
 // changes which patterns it matches, until we have chosen an arm.
 
-// compile-flags: -Zdisable-ast-check-for-mutation-in-guard
 
+#![feature(bind_by_move_pattern_guards)]
 #![feature(nll)]
 
 fn ok_mutation_in_guard(mut q: i32) {