ci: update Rust and Python versions used for testing

- Use latest stable for rustfmt and clippy.
- Update Rust in rust-toolchain and coredeps Docker container to 1.54.0
  and test against it.
- Test against 1.48.0 to ensure libdeltachat can be compiled with Debian
  bullseye "rustc" and "cargo".

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.50.0
+          toolchain: stable
           override: true
       - run: rustup component add rustfmt
       - uses: actions-rs/cargo@v1
@@ -32,7 +32,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
         with:
-            toolchain: 1.50.0
+            toolchain: stable
             components: clippy
             override: true
       - uses: actions-rs/clippy-check@v1
@@ -68,12 +68,23 @@ jobs:
     strategy:
       matrix:
         include:
+          # Currently used Rust version, same as in `rust-toolchain` file.
           - os: ubuntu-latest
-            rust: 1.50.0
-            python: 3.6
+            rust: 1.54.0
+            python: 3.9
           - os: windows-latest
-            rust: 1.50.0
+            rust: 1.54.0
             python: false # Python bindings compilation on Windows is not supported.
+
+          # Minimum Supported Rust Version = 1.48.0
+          # This is the Debian "bullseye" release version of Rust.
+          #
+          # Minimum Supported Python Version = 3.7
+          # This is the minimum version for which manylinux Python wheels are
+          # built.
+          - os: ubuntu-latest
+            rust: 1.48.0
+            python: 3.7
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@master

rust-toolchain

@@ -1 +1 @@
-1.50.0
+1.54.0

scripts/docker-coredeps-arm64/deps/build_rust.sh

@@ -8,9 +8,11 @@ set -e -x
 #
 # Avoid using rustup here as it depends on reading /proc/self/exe and
 # has problems running under QEMU.
-curl "https://static.rust-lang.org/dist/rust-1.52.1-$(uname -m)-unknown-linux-gnu.tar.gz" | tar xz
-cd "rust-1.52.1-$(uname -m)-unknown-linux-gnu"
+RUST_VERSION=1.54.0
+
+curl "https://static.rust-lang.org/dist/rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu.tar.gz" | tar xz
+cd "rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu"
 ./install.sh --prefix=/usr --components=rustc,cargo,"rust-std-$(uname -m)-unknown-linux-gnu"
 rustc --version
 cd ..
-rm -fr "rust-1.52.1-$(uname -m)-unknown-linux-gnu"
+rm -fr "rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu"

scripts/docker-coredeps/deps/build_rust.sh

@@ -3,9 +3,16 @@
 set -e -x
 
 # Install Rust
-curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain "1.50.0-$(uname -m)-unknown-linux-gnu" -y
-export PATH=/root/.cargo/bin:$PATH
-rustc --version
+#
+# Path from https://forge.rust-lang.org/infra/other-installation-methods.html
+#
+# Avoid using rustup here as it depends on reading /proc/self/exe and
+# has problems running under QEMU.
+RUST_VERSION=1.54.0
 
-# remove some 300-400 MB that we don't need for automated builds
-rm -rf "/root/.rustup/toolchains/1.50.0-$(uname -m)-unknown-linux-gnu/share"
+curl "https://static.rust-lang.org/dist/rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu.tar.gz" | tar xz
+cd "rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu"
+./install.sh --prefix=/usr --components=rustc,cargo,"rust-std-$(uname -m)-unknown-linux-gnu"
+rustc --version
+cd ..
+rm -fr "rust-${RUST_VERSION}-$(uname -m)-unknown-linux-gnu"