Add basic `miri` checks

We have a bit of `unsafe` code in the crates which should really be
checked with `miri`. Thus this adds a basic CI check that automatically
determines which crates need `miri` checking and checks them. It also
makes sure to enable all target features so that SIMD code can be
checked as well.

.github/workflows/miri.yml

@@ -0,0 +1,33 @@
+---   # rust-bitcoin CI: If you edit this file please update README.md
+on:   # yamllint disable-line rule:truthy
+  push:
+    branches:
+      - master
+      - 'test-ci/**'
+  pull_request:
+
+name: Miri
+
+jobs:
+  Miri:
+    name: Miri
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - name: "Checkout repo"
+        uses: actions/checkout@v4
+      - name: "Read nightly version"
+        id: read_toolchain
+        run: echo "nightly_version=$(cat nightly-version)" >> $GITHUB_OUTPUT
+      - name: "Select toolchain"
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ steps.read_toolchain.outputs.nightly_version }}
+          components: miri
+      - name: "Setup miri"
+        run: cargo miri setup
+      - name: "Set dependencies"
+        run: cp Cargo-recent.lock Cargo.lock
+      - name: "Run test script"
+        run: ./contrib/test-miri.sh

contrib/test-miri.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+set -euox pipefail
+
+cd "$(dirname "$0")/.."
+
+. contrib/test_vars.sh
+
+target_features="$(rustc --print target-features | awk '{ if ($1 == "") { exit 0 } if (NR != 1 && $1 != "crt-static") { if (NR == 2) { printf "+%s", $1 } else { printf ",+%s", $1 } } }')"
+
+for crate in $CRATES;
+do
+	# The secp256k1 crate cannot be miri-checked because of FFI, so we have to exclude it
+	if cargo tree --manifest-path "$crate/Cargo.toml" | grep -q secp256k1;
+	then
+		echo "$crate depends on secp256k1, skipping..." >&2
+		continue
+	fi
+	# Running miri is expensive and not needed for crates that don't contain unsafe
+	if RUSTFLAGS="-C target-feature=$target_features -F unsafe-code" cargo check -q --all-features --target x86_64-unknown-linux-gnu 2>/dev/null;
+	then
+		echo "No unsafe code in $crate, skipping..." >&2
+		continue
+	fi
+
+	RUSTFLAGS="-C target-feature=$target_features" RUSTDOCFLAGS="-C target-feature=$target_features" MIRIFLAGS=-Zmiri-backtrace=full cargo miri test --manifest-path "$crate/Cargo.toml" --all-features --target x86_64-unknown-linux-gnu
+done

nightly-version

@@ -1 +1 @@
-nightly-2024-09-04
+nightly-2024-09-07