Fix error spans for arguments to tuple enum constructors

Author: Nathan-Fenner

compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -714,12 +714,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     self.tcx.parent(expr_ctor_def_id)
                 }
                 hir::def::DefKind::Ctor(hir::def::CtorOf::Variant, hir::def::CtorKind::Fn) => {
-                    if in_ty_adt.did() == self.tcx.parent(expr_ctor_def_id) {
-                        // The constructor definition refers to the variant:
-                        // For example, for a local type `MyEnum::MyVariant` triggers this case.
-                        expr_ctor_def_id
-                    } else if in_ty_adt.did() == self.tcx.parent(self.tcx.parent(expr_ctor_def_id))
-                    {
+                    // For a typical enum like
+                    // `enum Blah<T> { Variant(T) }`
+                    // we get the following resolutions:
+                    // - expr_ctor_def_id :::                                   DefId(0:29 ~ source_file[b442]::Blah::Variant::{constructor#0})
+                    // - self.tcx.parent(expr_ctor_def_id) :::                  DefId(0:28 ~ source_file[b442]::Blah::Variant)
+                    // - self.tcx.parent(self.tcx.parent(expr_ctor_def_id)) ::: DefId(0:26 ~ source_file[b442]::Blah)
+
+                    // Therefore, we need to go up once to obtain the variant and up twice to obtain the type.
+                    // Note that this pattern still holds even when we `use` a variant or `use` an enum type to rename it, or chain `use` expressions
+                    // together; this resolution is handled automatically by `qpath_res`.
+
+                    // FIXME: Deal with type aliases?
+                    if in_ty_adt.did() == self.tcx.parent(self.tcx.parent(expr_ctor_def_id)) {
                         // The constructor definition refers to the "constructor" of the variant:
                         // For example, `Some(5)` triggers this case.
                         self.tcx.parent(expr_ctor_def_id)

tests/ui/errors/trait-bound-error-spans/blame-trait-error.rs

@@ -24,6 +24,31 @@ impl<'a, A: T1> T1 for &'a A {}
 
 fn want<V: T1>(_x: V) {}
 
+enum ExampleTuple<T> {
+    ExampleTupleVariant(T),
+}
+use ExampleDifferentTupleVariantName as ExampleYetAnotherTupleVariantName;
+use ExampleTuple as ExampleOtherTuple;
+use ExampleTuple::ExampleTupleVariant as ExampleDifferentTupleVariantName;
+use ExampleTuple::*;
+
+impl<A> T1 for ExampleTuple<A> where A: T3 {}
+
+enum ExampleStruct<T> {
+    ExampleStructVariant { field: T },
+}
+use ExampleDifferentStructVariantName as ExampleYetAnotherStructVariantName;
+use ExampleStruct as ExampleOtherStruct;
+use ExampleStruct::ExampleStructVariant as ExampleDifferentStructVariantName;
+use ExampleStruct::*;
+
+impl<A> T1 for ExampleStruct<A> where A: T3 {}
+
+struct ExampleActuallyTupleStruct<T>(T, i32);
+use ExampleActuallyTupleStruct as ExampleActuallyTupleStructOther;
+
+impl<A> T1 for ExampleActuallyTupleStruct<A> where A: T3 {}
+
 fn example<Q>(q: Q) {
     want(Wrapper { value: Burrito { filling: q } });
     //~^ ERROR the trait bound `Q: T3` is not satisfied [E0277]
@@ -36,6 +61,42 @@ fn example<Q>(q: Q) {
 
     want(&Some(q));
     //~^ ERROR `Q` is not an iterator [E0277]
+
+    want(&ExampleTuple::ExampleTupleVariant(q));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleTupleVariant(q));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleOtherTuple::ExampleTupleVariant(q));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleDifferentTupleVariantName(q));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleYetAnotherTupleVariantName(q));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleStruct::ExampleStructVariant { field: q });
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleStructVariant { field: q });
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleOtherStruct::ExampleStructVariant { field: q });
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleDifferentStructVariantName { field: q });
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleYetAnotherStructVariantName { field: q });
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleActuallyTupleStruct(q, 0));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
+
+    want(&ExampleActuallyTupleStructOther(q, 0));
+    //~^ ERROR `Q: T3` is not satisfied [E0277]
 }
 
 fn main() {}