curve: Fix no_std for fiat backend and add test for it

.github/workflows/curve25519-dalek.yml

@@ -3,10 +3,14 @@ name: curve25519 Rust
 on:
   push:
     branches: [ '**' ]
-    paths: 'curve25519-dalek/**'
+    paths:
+      - 'curve25519-dalek/**'
+      - '.github/workflows/curve25519-dalek.yml'
   pull_request:
     branches: [ '**' ]
-    paths: 'curve25519-dalek/**'
+    paths:
+      - 'curve25519-dalek/**'
+      - '.github/workflows/curve25519-dalek.yml'
 
 defaults:
   run:
@@ -39,6 +43,31 @@ jobs:
           RUSTFLAGS: '--cfg curve25519_dalek_backend="fiat"'
         run: cargo test --target ${{ matrix.target }}
 
+  # Default no_std test only tests using serial across all crates
+  build-nostd-fiat:
+    name: Build fiat on no_std target (thumbv7em-none-eabi)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - crate: curve25519-dalek
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: stable
+          targets: thumbv7em-none-eabi
+      - uses: taiki-e/install-action@cargo-hack
+      # No default features build
+      - name: no_std fiat / no feat ${{ matrix.crate }}
+        env:
+          RUSTFLAGS: '--cfg curve25519_dalek_backend="fiat"'
+        run: cargo build -p ${{ matrix.crate }} --target thumbv7em-none-eabi --release --no-default-features
+      - name: no_std fiat / cargo hack ${{ matrix.crate }}
+        env:
+          RUSTFLAGS: '--cfg curve25519_dalek_backend="fiat"'      
+        run: cargo hack build -p ${{ matrix.crate }} --target thumbv7em-none-eabi --release --each-feature --exclude-features default,std,getrandom
+
   test-serial:
     name: Test serial backend
     runs-on: ubuntu-latest

.github/workflows/workspace.yml

@@ -57,6 +57,29 @@ jobs:
     - name: Build default (host native) bench
       run: cargo build --benches
 
+  # Test no_std with serial (default)
+  build-nostd-serial:
+    name: Build serial on no_std target (thumbv7em-none-eabi)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - crate: curve25519-dalek
+          - crate: ed25519-dalek
+          - crate: x25519-dalek
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: stable
+          targets: thumbv7em-none-eabi
+      - uses: taiki-e/install-action@cargo-hack
+      # No default features build
+      - name: no_std / no feat ${{ matrix.crate }}
+        run: cargo build -p ${{ matrix.crate }} --target thumbv7em-none-eabi --release --no-default-features
+      - name: no_std / cargo hack ${{ matrix.crate }}
+        run: cargo hack build -p ${{ matrix.crate }} --target thumbv7em-none-eabi --release --each-feature --exclude-features default,std,getrandom
+
   clippy:
     name: Check that clippy is happy
     runs-on: ubuntu-latest

curve25519-dalek/Cargo.toml

@@ -59,7 +59,7 @@ zeroize = { version = "1", default-features = false, optional = true }
 cpufeatures = "0.2.6"
 
 [target.'cfg(curve25519_dalek_backend = "fiat")'.dependencies]
-fiat-crypto = "0.1.19"
+fiat-crypto = { version = "0.1.19", default-features = false }
 
 [features]
 default = ["alloc", "precomputed-tables", "zeroize"]