Auto merge of #50224 - pietroalbini:beta-backports, r=alexcrichton

[beta] Process backports

* #49779: Don't report compile-time errors for promoteds
* #50110: Warn on all erroneous constants

Author: bors

src/librustc_lint/builtin.rs

@@ -1430,3 +1430,71 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
         }
     }
 }
+
+/// Lint constants that are erroneous.
+/// Without this lint, we might not get any diagnostic if the constant is
+/// unused within this crate, even though downstream crates can't use it
+/// without producing an error.
+pub struct UnusedBrokenConst;
+
+impl LintPass for UnusedBrokenConst {
+    fn get_lints(&self) -> LintArray {
+        lint_array!()
+    }
+}
+
+fn check_const(cx: &LateContext, body_id: hir::BodyId, what: &str) {
+    let def_id = cx.tcx.hir.body_owner_def_id(body_id);
+    let param_env = cx.tcx.param_env(def_id);
+    let cid = ::rustc::mir::interpret::GlobalId {
+        instance: ty::Instance::mono(cx.tcx, def_id),
+        promoted: None
+    };
+    if let Err(err) = cx.tcx.const_eval(param_env.and(cid)) {
+        let span = cx.tcx.def_span(def_id);
+        let mut diag = cx.struct_span_lint(
+            CONST_ERR,
+            span,
+            &format!("this {} cannot be used", what),
+        );
+        use rustc::middle::const_val::ConstEvalErrDescription;
+        match err.description() {
+            ConstEvalErrDescription::Simple(message) => {
+                diag.span_label(span, message);
+            }
+            ConstEvalErrDescription::Backtrace(miri, frames) => {
+                diag.span_label(span, format!("{}", miri));
+                for frame in frames {
+                    diag.span_label(frame.span, format!("inside call to `{}`", frame.location));
+                }
+            }
+        }
+        diag.emit()
+    }
+}
+
+struct UnusedBrokenConstVisitor<'a, 'tcx: 'a>(&'a LateContext<'a, 'tcx>);
+
+impl<'a, 'tcx, 'v> hir::intravisit::Visitor<'v> for UnusedBrokenConstVisitor<'a, 'tcx> {
+    fn visit_nested_body(&mut self, id: hir::BodyId) {
+        check_const(self.0, id, "array length");
+    }
+    fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
+        hir::intravisit::NestedVisitorMap::None
+    }
+}
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
+    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
+        match it.node {
+            hir::ItemConst(_, body_id) => {
+                check_const(cx, body_id, "constant");
+            },
+            hir::ItemTy(ref ty, _) => hir::intravisit::walk_ty(
+                &mut UnusedBrokenConstVisitor(cx),
+                ty
+            ),
+            _ => {},
+        }
+    }
+}

src/librustc_lint/lib.rs

@@ -139,6 +139,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                  UnionsWithDropFields,
                  UnreachablePub,
                  TypeAliasBounds,
+                 UnusedBrokenConst,
                  );
 
     add_builtin_with_new!(sess,

src/librustc_mir/interpret/const_eval.rs

@@ -56,7 +56,7 @@ pub fn mk_eval_cx<'a, 'tcx>(
     Ok(ecx)
 }
 
-pub fn eval_body_with_mir<'a, 'mir, 'tcx>(
+pub fn eval_promoted<'a, 'mir, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     cid: GlobalId<'tcx>,
     mir: &'mir mir::Mir<'tcx>,
@@ -66,7 +66,7 @@ pub fn eval_body_with_mir<'a, 'mir, 'tcx>(
     match res {
         Ok(val) => Some(val),
         Err(mut err) => {
-            ecx.report(&mut err, true, None);
+            ecx.report(&mut err, false, None);
             None
         }
     }

src/librustc_mir/interpret/mod.rs

@@ -19,7 +19,7 @@ pub use self::place::{Place, PlaceExtra};
 pub use self::memory::{Memory, MemoryKind, HasMemory};
 
 pub use self::const_eval::{
-    eval_body_with_mir,
+    eval_promoted,
     mk_borrowck_eval_cx,
     eval_body,
     CompileTimeEvaluator,

src/librustc_mir/monomorphize/collector.rs

@@ -1146,17 +1146,15 @@ fn collect_neighbours<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         param_substs: instance.substs,
     }.visit_mir(&mir);
     let param_env = ty::ParamEnv::reveal_all();
-    for (i, promoted) in mir.promoted.iter().enumerate() {
+    for i in 0..mir.promoted.len() {
         use rustc_data_structures::indexed_vec::Idx;
         let cid = GlobalId {
             instance,
             promoted: Some(Promoted::new(i)),
         };
         match tcx.const_eval(param_env.and(cid)) {
             Ok(val) => collect_const(tcx, val, instance.substs, output),
-            Err(err) => {
-                err.report(tcx, promoted.span, "promoted");
-            }
+            Err(_) => {},
         }
     }
 }

src/librustc_mir/transform/const_prop.rs

@@ -20,7 +20,7 @@ use rustc::mir::visit::{Visitor, PlaceContext};
 use rustc::middle::const_val::ConstVal;
 use rustc::ty::{TyCtxt, self, Instance};
 use rustc::mir::interpret::{Value, PrimVal, GlobalId};
-use interpret::{eval_body_with_mir, mk_borrowck_eval_cx, ValTy};
+use interpret::{eval_promoted, mk_borrowck_eval_cx, ValTy};
 use transform::{MirPass, MirSource};
 use syntax::codemap::Span;
 use rustc::ty::subst::Substs;
@@ -161,7 +161,7 @@ impl<'b, 'a, 'tcx:'b> ConstPropagator<'b, 'a, 'tcx> {
                 };
                 // cannot use `const_eval` here, because that would require having the MIR
                 // for the current function available, but we're producing said MIR right now
-                let (value, _, ty) = eval_body_with_mir(self.tcx, cid, self.mir, self.param_env)?;
+                let (value, _, ty) = eval_promoted(self.tcx, cid, self.mir, self.param_env)?;
                 let val = (value, ty, c.span);
                 trace!("evaluated {:?} to {:?}", c, val);
                 Some(val)

src/librustc_trans/mir/operand.rs

@@ -399,7 +399,14 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
                 self.mir_constant_to_miri_value(bx, constant)
                     .and_then(|c| OperandRef::from_const(bx, c, ty))
                     .unwrap_or_else(|err| {
-                        err.report(bx.tcx(), constant.span, "const operand");
+                        match constant.literal {
+                            mir::Literal::Promoted { .. } => {
+                                // don't report errors inside promoteds, just warnings.
+                            },
+                            mir::Literal::Value { .. } => {
+                                err.report(bx.tcx(), constant.span, "const operand")
+                            },
+                        }
                         // We've errored, so we don't have to produce working code.
                         let layout = bx.cx.layout_of(ty);
                         PlaceRef::new_sized(

src/test/compile-fail/array_const_index-0.rs

@@ -12,6 +12,7 @@ const A: &'static [i32] = &[];
 const B: i32 = (&A)[1];
 //~^ ERROR constant evaluation error
 //~| index out of bounds: the len is 0 but the index is 1
+//~| WARN this constant cannot be used
 
 fn main() {
     let _ = B;

src/test/compile-fail/array_const_index-1.rs

@@ -12,6 +12,7 @@ const A: [i32; 0] = [];
 const B: i32 = A[1];
 //~^ ERROR constant evaluation error
 //~| index out of bounds: the len is 0 but the index is 1
+//~| WARN this constant cannot be used
 
 fn main() {
     let _ = B;

src/test/compile-fail/const-err-early.rs

@@ -10,17 +10,17 @@
 
 #![deny(const_err)]
 
-pub const A: i8 = -std::i8::MIN; //~ ERROR E0080
-//~^ ERROR attempt to negate with overflow
+pub const A: i8 = -std::i8::MIN; //~ ERROR const_err
+//~^ ERROR this constant cannot be used
 //~| ERROR constant evaluation error
-pub const B: u8 = 200u8 + 200u8; //~ ERROR E0080
-//~^ ERROR attempt to add with overflow
-pub const C: u8 = 200u8 * 4; //~ ERROR E0080
-//~^ ERROR attempt to multiply with overflow
-pub const D: u8 = 42u8 - (42u8 + 1); //~ ERROR E0080
-//~^ ERROR attempt to subtract with overflow
+pub const B: u8 = 200u8 + 200u8; //~ ERROR const_err
+//~^ ERROR this constant cannot be used
+pub const C: u8 = 200u8 * 4; //~ ERROR const_err
+//~^ ERROR this constant cannot be used
+pub const D: u8 = 42u8 - (42u8 + 1); //~ ERROR const_err
+//~^ ERROR this constant cannot be used
 pub const E: u8 = [5u8][1];
-//~^ ERROR E0080
+//~^ ERROR const_err
 
 fn main() {
     let _a = A;