Fix miri validation errors through now stricter provenance

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ on:
 
 name: Continuous integration
 
+env:
+  MIRIFLAGS: -Zmiri-strict-provenance
+
 jobs:
   check:
     name: Check
@@ -126,3 +129,17 @@ jobs:
         with:
           command: clippy
           args: -- -D warnings
+  miri:
+    name: Miri
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          components: miri
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: miri
+          args: test

src/context.rs

@@ -1,4 +1,4 @@
-use crate::error::ContextError;
+use crate::error::{ContextError, ErrorImpl};
 use crate::{ContextCompat, Report, StdError, WrapErr};
 use core::fmt::{self, Debug, Display, Write};
 
@@ -158,7 +158,7 @@ where
     D: Display,
 {
     fn source(&self) -> Option<&(dyn StdError + 'static)> {
-        Some(self.error.inner.error())
+        Some(ErrorImpl::error(self.error.inner.as_ref()))
     }
 }