Fix miri validation errors through now stricter provenance (#103)

* fix(miri): box transmute and invalid references

The general causes for the miri invalidation is the prevelant use of
`Box` and its references to `ErrorImpl<()>`.

`mem::transmute` does not preserve the tag stack for transmuting the
boxes.

Additionally, having references to `ErrorImpl<()>` which has a different
layout than the allocation or `ErrorImpl<E>` for some unknown `E`. This
causes the new "untyped" reference to now have a provenance that
includes the size of E and thus is outside the provenance.

* fix(miri): downcast_mut using `&mut _ => *const _ => *mut`

* fix(miri): stub file reading

* fix(miri): don't construct temp references of shunk provenance

* ci: miri

* fix: `unsafe_op_in_unsafe_fn`

* chore!: bump MSRV

* chore: address PR comments

* fix: ci workflow names

* chore: raise msrv to 1.65 (addr2line)

* chore: revert distinctive CI names due to branch protection rules

The new names, such as `Test Platform Matrix` which do make it easier to
see which jobs failed, rather than msrv, test, and miri all being called
`Test Suite`, the in-place branch protection rules wait forever until
the now non-existent `Test Suite` passes

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ on:
 
 name: Continuous integration
 
+env:
+  MIRIFLAGS: -Zmiri-strict-provenance
+
 jobs:
   check:
     name: Check
@@ -66,7 +69,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.42
+          toolchain: 1.65
           override: true
       - uses: actions-rs/cargo@v1
         with:
@@ -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

Cargo.toml

@@ -27,7 +27,7 @@ pyo3 = { version = "0.13", default-features = false, features = ["auto-initializ
 
 [dependencies]
 indenter = "0.3.0"
-once_cell = "1.4.0"
+once_cell = "1.18.0"
 pyo3 = { version = "0.13", optional = true, default-features = false }
 
 [package.metadata.docs.rs]

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()))
     }
 }