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authorbors <bors@rust-lang.org>2020-04-17 04:15:18 +0000
committerbors <bors@rust-lang.org>2020-04-17 04:15:18 +0000
commit861996e13820a2e401df60756a373606b50948e5 (patch)
tree7b70bbcac40629669a01366657b05d910289c77b /src/librustc_error_codes/error_codes
parent318726b301db2a0718d05f166d3d6c578273189c (diff)
parent65243a8f7c03425c399d990d0802e4506bbcd754 (diff)
Auto merge of #71230 - Dylan-DPC:rollup-rofigbv, r=Dylan-DPC
Rollup of 7 pull requests

Successful merges:

 - #70578 (Add long error explanation for E0657)
 - #70910 (Hides default fns inside Fuse impl to avoid exposing it to any crate)
 - #71164 (reword Miri validity errors: undefined -> uninitialized)
 - #71182 (Add some regression tests)
 - #71206 (Miri error messages: avoid try terminology)
 - #71220 (Dogfood or_patterns in the standard library)
 - #71225 (Fix typo in Default trait docs: Provides -> Provide)

Failed merges:

r? @ghost
Diffstat (limited to 'src/librustc_error_codes/error_codes')
-rw-r--r--src/librustc_error_codes/error_codes/E0657.md57
1 files changed, 57 insertions, 0 deletions
diff --git a/src/librustc_error_codes/error_codes/E0657.md b/src/librustc_error_codes/error_codes/E0657.md
new file mode 100644
index 00000000000..7fe48c51147
--- /dev/null
+++ b/src/librustc_error_codes/error_codes/E0657.md
@@ -0,0 +1,57 @@
+A lifetime bound on a trait implementation was captured at an incorrect place.
+
+Erroneous code example:
+
+```compile_fail,E0657
+trait Id<T> {}
+trait Lt<'a> {}
+
+impl<'a> Lt<'a> for () {}
+impl<T> Id<T> for T {}
+
+fn free_fn_capture_hrtb_in_impl_trait()
+    -> Box<for<'a> Id<impl Lt<'a>>> // error!
+{
+    Box::new(())
+}
+
+struct Foo;
+impl Foo {
+    fn impl_fn_capture_hrtb_in_impl_trait()
+        -> Box<for<'a> Id<impl Lt<'a>>> // error!
+    {
+        Box::new(())
+    }
+}
+```
+
+Here, you have used the inappropriate lifetime in the `impl Trait`,
+The `impl Trait` can only capture lifetimes bound at the fn or impl
+level.
+
+To fix this we have to define the lifetime at the function or impl
+level and use that lifetime in the `impl Trait`. For example you can
+define the lifetime at the function:
+
+```
+trait Id<T> {}
+trait Lt<'a> {}
+
+impl<'a> Lt<'a> for () {}
+impl<T> Id<T> for T {}
+
+fn free_fn_capture_hrtb_in_impl_trait<'b>()
+    -> Box<for<'a> Id<impl Lt<'b>>> // ok!
+{
+    Box::new(())
+}
+
+struct Foo;
+impl Foo {
+    fn impl_fn_capture_hrtb_in_impl_trait<'b>()
+        -> Box<for<'a> Id<impl Lt<'b>>> // ok!
+    {
+        Box::new(())
+    }
+}
+```