Add correct span for unsized types

Author: silentvein

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -269,6 +269,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             (err_msg, None)
                         };
 
+                        if tcx.is_lang_item(leaf_trait_predicate.def_id(), LangItem::Sized) {
+                            if let Some(refined_span) = self.report_sized_item(span, leaf_trait_predicate) {
+                                span = refined_span;
+                            }
+                        }
+
                         let mut err = struct_span_code_err!(self.dcx(), span, E0277, "{}", err_msg);
                         *err.long_ty_path() = long_ty_file;
 
@@ -769,6 +775,48 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         applied_do_not_recommend
     }
 
+    fn report_sized_item(
+        &self,
+        span: Span,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    ) -> Option<Span> {
+        let source_map = self.tcx.sess.source_map();
+        let snippet = source_map.span_to_snippet(span).ok()?;
+
+        // Skip macro
+        if snippet.contains('!') {
+            return None;
+        }
+
+        let self_ty = trait_pred.skip_binder().self_ty().to_string();
+
+        // Try to find the exact type in the source code
+        if let Some(pos) = snippet.find(&self_ty) {
+            let start = span.lo() + BytePos(pos as u32);
+            let end = start + BytePos(self_ty.len() as u32);
+            return Some(Span::new(start, end, span.ctxt(), span.parent()));
+        }
+
+        // Sanity check if exact match fails
+        let mut core_type = self_ty.as_str();
+        while core_type.starts_with('[') && core_type.ends_with(']') {
+            core_type = &core_type[1..core_type.len() - 1].trim();
+            if let Some(pos) = core_type.find(';') {
+                core_type = &core_type[..pos].trim();
+            }
+        }
+
+        // Try to find core type
+        if core_type != self_ty && !core_type.is_empty() {
+            if let Some(pos) = snippet.find(&core_type) {
+                let start = span.lo() + BytePos(pos as u32);
+                let end = start + BytePos(core_type.len() as u32);
+                return Some(Span::new(start, end, span.ctxt(), span.parent()));
+            }
+        }
+        None
+    }
+
     fn report_host_effect_error(
         &self,
         predicate: ty::Binder<'tcx, ty::HostEffectPredicate<'tcx>>,

tests/ui/abi/debug.stderr

@@ -876,10 +876,10 @@ LL | type TestAbiNeSign = (fn(i32), fn(u32));
    | ^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/debug.rs:64:46
+  --> $DIR/debug.rs:64:47
    |
 LL | type TestAbiEqNonsense = (fn((str, str)), fn((str, str)));
-   |                                              ^^^^^^^^^^ doesn't have a size known at compile-time
+   |                                               ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: only the last element of a tuple may have a dynamically sized type

tests/ui/associated-types/defaults-wf.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
-  --> $DIR/defaults-wf.rs:7:15
+  --> $DIR/defaults-wf.rs:7:19
    |
 LL |     type Ty = Vec<[u8]>;
-   |               ^^^^^^^^^ doesn't have a size known at compile-time
+   |                   ^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
 note: required by an implicit `Sized` bound in `Vec`

tests/ui/associated-types/issue-20005.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `Self` cannot be known at compilation time
-  --> $DIR/issue-20005.rs:10:49
+  --> $DIR/issue-20005.rs:10:54
    |
 LL |     ) -> <Dst as From<Self>>::Result where Dst: From<Self> {
-   |                                                 ^^^^^^^^^^ doesn't have a size known at compile-time
+   |                                                      ^^^^ doesn't have a size known at compile-time
    |
 note: required by an implicit `Sized` bound in `From`
   --> $DIR/issue-20005.rs:1:12

tests/ui/associated-types/trait-with-supertraits-needing-sized-self.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `Self` cannot be known at compilation time
-  --> $DIR/trait-with-supertraits-needing-sized-self.rs:3:22
+  --> $DIR/trait-with-supertraits-needing-sized-self.rs:3:33
    |
 LL | trait ArithmeticOps: Add<Output=Self> + Sub<Output=Self> + Mul<Output=Self> + Div<Output=Self> {}
-   |                      ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                                 ^^^^ doesn't have a size known at compile-time
    |
 note: required by an implicit `Sized` bound in `Add`
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL

tests/ui/cast/unsized-union-ice.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
-  --> $DIR/unsized-union-ice.rs:6:10
+  --> $DIR/unsized-union-ice.rs:6:33
    |
 LL |     val: std::mem::ManuallyDrop<[u8]>,
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                                 ^^^^ doesn't have a size known at compile-time
    |
    = help: within `ManuallyDrop<[u8]>`, the trait `Sized` is not implemented for `[u8]`
 note: required because it appears within the type `ManuallyDrop<[u8]>`

tests/ui/closures/closure-return-type-must-be-sized.stderr

@@ -1,17 +1,17 @@
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:54:5
+  --> $DIR/closure-return-type-must-be-sized.rs:54:22
    |
 LL |     a::foo::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:55:14
+  --> $DIR/closure-return-type-must-be-sized.rs:55:22
    |
 LL |     a::bar::<fn() -> dyn A, _>();
-   |              ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
@@ -22,28 +22,28 @@ LL |     pub fn bar<F: FnOnce() -> R, R: ?Sized>() {}
    |                   ^^^^^^^^^^^^^ required by this bound in `bar`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:56:5
+  --> $DIR/closure-return-type-must-be-sized.rs:56:22
    |
 LL |     a::baz::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:61:5
+  --> $DIR/closure-return-type-must-be-sized.rs:61:22
    |
 LL |     b::foo::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:62:14
+  --> $DIR/closure-return-type-must-be-sized.rs:62:22
    |
 LL |     b::bar::<fn() -> dyn A, _>();
-   |              ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
@@ -54,28 +54,28 @@ LL |     pub fn bar<F: Fn() -> R, R: ?Sized>() {}
    |                   ^^^^^^^^^ required by this bound in `bar`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:63:5
+  --> $DIR/closure-return-type-must-be-sized.rs:63:22
    |
 LL |     b::baz::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:68:5
+  --> $DIR/closure-return-type-must-be-sized.rs:68:22
    |
 LL |     c::foo::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:69:14
+  --> $DIR/closure-return-type-must-be-sized.rs:69:22
    |
 LL |     c::bar::<fn() -> dyn A, _>();
-   |              ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`
@@ -86,10 +86,10 @@ LL |     pub fn bar<F: FnMut() -> R, R: ?Sized>() {}
    |                   ^^^^^^^^^^^^ required by this bound in `bar`
 
 error[E0277]: the size for values of type `dyn A` cannot be known at compilation time
-  --> $DIR/closure-return-type-must-be-sized.rs:70:5
+  --> $DIR/closure-return-type-must-be-sized.rs:70:22
    |
 LL |     c::baz::<fn() -> dyn A>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                      ^^^^^ doesn't have a size known at compile-time
    |
    = help: within `fn() -> dyn A`, the trait `Sized` is not implemented for `dyn A`
    = note: required because it appears within the type `fn() -> dyn A`

tests/ui/closures/missing-body.stderr

@@ -5,10 +5,10 @@ LL | fn main() { |b: [str; _]| {}; }
    |                       ^ not allowed in type signatures
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/missing-body.rs:5:17
+  --> $DIR/missing-body.rs:5:18
    |
 LL | fn main() { |b: [str; _]| {}; }
-   |                 ^^^^^^^^ doesn't have a size known at compile-time
+   |                  ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: slice and array elements must have `Sized` type

tests/ui/consts/const-unsized.stderr

@@ -26,10 +26,10 @@ LL | static STATIC_1: dyn Debug + Sync = *(&1 as &(dyn Debug + Sync));
    = note: statics and constants must have a statically known size
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/const-unsized.rs:15:1
+  --> $DIR/const-unsized.rs:15:20
    |
 LL | static STATIC_BAR: str = *"bar";
-   | ^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                    ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: statics and constants must have a statically known size

tests/ui/consts/dont-ctfe-unsized-initializer.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `str` cannot be known at compilation time
-  --> $DIR/dont-ctfe-unsized-initializer.rs:1:1
+  --> $DIR/dont-ctfe-unsized-initializer.rs:1:11
    |
 LL | static S: str = todo!();
-   | ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |           ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: statics and constants must have a statically known size