Merge #51: Add no-std tests

1747c8a Add no-std tests (Nick Johnson)
0ad6c7d Fix integration lock file (Nick Johnson)

Pull request description:

  Testing out the new cargo-rbmt thing where it tests no-std if it detects it. Required switching to `#![no_std]` since cargo-rbmt doesn't do any parsing, but this is kind of easier to read anyways?

  Not sure how terrible it is to have to install the ARM compiler like this.

ACKs for top commit:
  tcharding:
    ACK 1747c8a

Tree-SHA512: 4c16cbe72f1638f516aa1afdbdad178d4ef4031d7bdb0bd63fa173f99ba37eb9d2a4f7e937b64fec4edf59b4433446ae3070c369283119af93f946ac205a27e9

Author: tcharding

.github/actions/prepare/action.yml

@@ -12,23 +12,26 @@ inputs:
 runs:
   using: "composite"
   steps:
+    - name: "Install ARM cross-compiler for no-std"
+      shell: bash
+      run: |
+        sudo apt-get update && sudo apt-get install -y gcc-arm-none-eabi
+        echo "CC_thumbv7m_none_eabi=arm-none-eabi-gcc" >> $GITHUB_ENV
+
     - name: "Determine toolchain"
       id: toolchain
       shell: bash
       run: |
-        if [ "${{ inputs.toolchain }}" = "nightly" ]; then
-          TOOLCHAIN="$(cat nightly-version)"
-        else
-          TOOLCHAIN="${{ inputs.toolchain }}"
-        fi
+        [[ "${{ inputs.toolchain }}" == "nightly" ]] && TOOLCHAIN=$(cat nightly-version) || TOOLCHAIN="${{ inputs.toolchain }}"
         echo "version=$TOOLCHAIN" >> $GITHUB_OUTPUT
 
     - name: "Setup requested toolchain"
       uses: actions-rust-lang/setup-rust-toolchain@v1
       with:
-        toolchain: ${{ steps.toolchain.outputs.version }}
+        toolchain: stable,${{ steps.toolchain.outputs.version }}
         components: ${{ inputs.components }}
+        target: thumbv7m-none-eabi
 
     - name: "Install RBMT"
       shell: bash
-      run: cargo install --git https://github.com/rust-bitcoin/rust-bitcoin-maintainer-tools.git --rev "$(cat rbmt-version)" cargo-rbmt --locked
+      run: cargo +stable install --git https://github.com/rust-bitcoin/rust-bitcoin-maintainer-tools.git --rev "$(cat rbmt-version)" cargo-rbmt --locked

.gitignore

@@ -1,8 +1,7 @@
 # .gitignore for rust-psbt repository.
 
-# Lock files
-Cargo.lock
+# Ignore library lock file.
+/Cargo.lock
 
 # Build artifacts
 target
-