Never stop due to errors before borrow checking

Author: estebank

src/librustc_interface/passes.rs

@@ -936,13 +936,6 @@ fn analysis<'tcx>(
         });
     });
 
-    // Abort so we don't try to construct MIR with liveness errors.
-    // We also won't want to continue with errors from rvalue promotion
-    // We only do so if the only error found so far *isn't* a missing `fn main()`
-    if !(entry_point.is_none() && sess.err_count() == 1) {
-        tcx.sess.abort_if_errors();
-    }
-
     time(sess, "borrow checking", || {
         if tcx.use_ast_borrowck() {
             borrowck::check_crate(tcx);

src/librustc_mir/hair/pattern/check_match.rs

@@ -603,7 +603,9 @@ fn check_legality_of_move_bindings(
             E0009,
             "cannot bind by-move and by-ref in the same pattern",
         );
-        err.span_label(by_ref_span.unwrap(), "both by-ref and by-move used");
+        if let Some(by_ref_span) = by_ref_span {
+            err.span_label(by_ref_span, "both by-ref and by-move used");
+        }
         for span in span_vec.iter(){
             err.span_label(*span, "by-move pattern here");
         }

src/librustc_mir/transform/qualify_consts.rs

@@ -1502,9 +1502,11 @@ impl MirPass for QualifyAndPromoteConstants {
                                 tcx.sess,
                                 span,
                                 E0723,
-                                "{} (see issue #57563)",
+                                "{}",
                                 err,
                             );
+                            diag.note("for more information, see issue \
+                                       https://github.com/rust-lang/rust/issues/57563");
                             diag.help(
                                 "add #![feature(const_fn)] to the crate attributes to enable",
                             );

src/test/ui/borrowck/borrowck-mutate-in-guard.rs

@@ -9,9 +9,15 @@ fn foo() -> isize {
     match x {
         Enum::A(_) if { x = Enum::B(false); false } => 1,
         //~^ ERROR cannot assign in a pattern guard
+        //~| WARN cannot assign `x` in match guard
+        //~| WARN this error has been downgraded to a warning for backwards compatibility
+        //~| WARN this represents potential undefined behavior in your code and this warning will
         Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
         //~^ ERROR cannot mutably borrow in a pattern guard
-        //~^^ ERROR cannot assign in a pattern guard
+        //~| ERROR cannot assign in a pattern guard
+        //~| WARN cannot mutably borrow `x` in match guard
+        //~| WARN this error has been downgraded to a warning for backwards compatibility
+        //~| WARN this represents potential undefined behavior in your code and this warning will
         Enum::A(p) => *p,
         Enum::B(_) => 2,
     }

src/test/ui/borrowck/borrowck-mutate-in-guard.stderr

@@ -5,20 +5,43 @@ LL |         Enum::A(_) if { x = Enum::B(false); false } => 1,
    |                         ^^^^^^^^^^^^^^^^^^ assignment in pattern guard
 
 error[E0301]: cannot mutably borrow in a pattern guard
-  --> $DIR/borrowck-mutate-in-guard.rs:12:38
+  --> $DIR/borrowck-mutate-in-guard.rs:15:38
    |
 LL |         Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
    |                                      ^ borrowed mutably in pattern guard
    |
    = help: add #![feature(bind_by_move_pattern_guards)] to the crate attributes to enable
 
 error[E0302]: cannot assign in a pattern guard
-  --> $DIR/borrowck-mutate-in-guard.rs:12:41
+  --> $DIR/borrowck-mutate-in-guard.rs:15:41
    |
 LL |         Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
    |                                         ^^^^^^^^^^^^^^^^^^^ assignment in pattern guard
 
+warning[E0510]: cannot assign `x` in match guard
+  --> $DIR/borrowck-mutate-in-guard.rs:10:25
+   |
+LL |     match x {
+   |           - value is immutable in match guard
+LL |         Enum::A(_) if { x = Enum::B(false); false } => 1,
+   |                         ^^^^^^^^^^^^^^^^^^ cannot assign
+   |
+   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
+   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+
+warning[E0510]: cannot mutably borrow `x` in match guard
+  --> $DIR/borrowck-mutate-in-guard.rs:15:33
+   |
+LL |     match x {
+   |           - value is immutable in match guard
+...
+LL |         Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
+   |                                 ^^^^^^ cannot mutably borrow
+   |
+   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
+   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+
 error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0301, E0302.
+Some errors have detailed explanations: E0301, E0302, E0510.
 For more information about an error, try `rustc --explain E0301`.

src/test/ui/consts/const_let_refutable.rs

@@ -1,5 +1,11 @@
 fn main() {}
 
 const fn slice([a, b]: &[i32]) -> i32 { //~ ERROR refutable pattern in function argument
-    a + b
+    a + b //~ ERROR can only call other `const fn` within a `const fn`
+    //~^ WARN use of possibly uninitialized variable: `a`
+    //~| WARN this error has been downgraded to a warning for backwards compatibility
+    //~| WARN this represents potential undefined behavior in your code and this warning will
+    //~| WARN use of possibly uninitialized variable: `b`
+    //~| WARN this error has been downgraded to a warning for backwards compatibility
+    //~| WARN this represents potential undefined behavior in your code and this warning will
 }

src/test/ui/consts/const_let_refutable.stderr

@@ -4,6 +4,34 @@ error[E0005]: refutable pattern in function argument: `&[]` not covered
 LL | const fn slice([a, b]: &[i32]) -> i32 {
    |                ^^^^^^ pattern `&[]` not covered
 
-error: aborting due to previous error
+error[E0723]: can only call other `const fn` within a `const fn`, but `const std::ops::Add::add` is not stable as `const fn`
+  --> $DIR/const_let_refutable.rs:4:5
+   |
+LL |     a + b
+   |     ^^^^^
+   |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
+   = help: add #![feature(const_fn)] to the crate attributes to enable
+
+warning[E0381]: use of possibly uninitialized variable: `a`
+  --> $DIR/const_let_refutable.rs:4:5
+   |
+LL |     a + b
+   |     ^ use of possibly uninitialized `a`
+   |
+   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
+   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+
+warning[E0381]: use of possibly uninitialized variable: `b`
+  --> $DIR/const_let_refutable.rs:4:9
+   |
+LL |     a + b
+   |         ^ use of possibly uninitialized `b`
+   |
+   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
+   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0005`.
+Some errors have detailed explanations: E0005, E0381, E0723.
+For more information about an error, try `rustc --explain E0005`.

src/test/ui/consts/match_ice.stderr

@@ -1,11 +1,17 @@
 error[E0004]: non-exhaustive patterns: `&S` not covered
-  --> $DIR/match_ice.rs:7:11
+  --> $DIR/match_ice.rs:8:11
    |
 LL |     match C {
    |           ^ pattern `&S` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error: aborting due to previous error
+error[E0277]: can't compare `S` with `S`
+   |
+   = help: the trait `std::cmp::PartialEq` is not implemented for `S`
+   = note: required because of the requirements on the impl of `std::cmp::PartialEq` for `&S`
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0004`.
+Some errors occurred: E0004, E0277.
+For more information about an error, try `rustc --explain E0004`.

src/test/ui/consts/min_const_fn/bad_const_fn_body_ice.stderr

@@ -1,9 +1,10 @@
-error[E0723]: heap allocations are not allowed in const fn (see issue #57563)
+error[E0723]: heap allocations are not allowed in const fn
   --> $DIR/bad_const_fn_body_ice.rs:2:5
    |
 LL |     vec![1, 2, 3]
    |     ^^^^^^^^^^^^^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 

src/test/ui/consts/min_const_fn/cast_errors.stderr

@@ -1,41 +1,46 @@
-error[E0723]: unsizing casts are not allowed in const fn (see issue #57563)
+error[E0723]: unsizing casts are not allowed in const fn
   --> $DIR/cast_errors.rs:3:41
    |
 LL | const fn unsize(x: &[u8; 3]) -> &[u8] { x }
    |                                         ^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error[E0723]: function pointers in const fn are unstable (see issue #57563)
+error[E0723]: function pointers in const fn are unstable
   --> $DIR/cast_errors.rs:5:23
    |
 LL | const fn closure() -> fn() { || {} }
    |                       ^^^^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error[E0723]: function pointers in const fn are unstable (see issue #57563)
+error[E0723]: function pointers in const fn are unstable
   --> $DIR/cast_errors.rs:8:5
    |
 LL |     (|| {}) as fn();
    |     ^^^^^^^^^^^^^^^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error[E0723]: function pointers in const fn are unstable (see issue #57563)
+error[E0723]: function pointers in const fn are unstable
   --> $DIR/cast_errors.rs:11:28
    |
 LL | const fn reify(f: fn()) -> unsafe fn() { f }
    |                            ^^^^^^^^^^^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error[E0723]: function pointers in const fn are unstable (see issue #57563)
+error[E0723]: function pointers in const fn are unstable
   --> $DIR/cast_errors.rs:13:21
    |
 LL | const fn reify2() { main as unsafe fn(); }
    |                     ^^^^^^^^^^^^^^^^^^^
    |
+   = note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
 error: aborting due to 5 previous errors