Use Dusk compiler for contracts

The compiler is downloaded and extracted to the target directory, and
linked to the toolchains in the rustup directory, making it available to
be used anyone in the system.

The compiler is available as under the `+dusk` option in rust tools, and
is able to compile at least the `wasm32-unknown-unknown` target.

See-also: #280

Makefile

@@ -1,9 +1,14 @@
 help: ## Display this help screen
 	@grep -h -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-15s\033[0m %s\n", $$1, $$2}'
 
-contracts: ## Build example contracts
+COMPILER_VERSION=v0.0.0
+
+setup-compiler: ## Setup the Dusk Contract Compiler
+	@./scripts/setup-compiler.sh $(COMPILER_VERSION)
+
+contracts: setup-compiler ## Build example contracts
 	@RUSTFLAGS="-C link-args=-zstack-size=65536" \
-	cargo build \
+	cargo +dusk build \
 	  --release \
 	  --manifest-path=contracts/Cargo.toml \
 	  --color=always \

scripts/setup-compiler.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+
+# The script should check whether the inputs are set, or print usage
+# information otherwise.
+if [ -z "$1" ]; then
+    echo "Usage: $0 <compiler-version>"
+    exit 1
+fi
+
+RELEASES_URL=https://github.com/dusk-network/rust/releases/download
+
+COMPILER_VERSION=$1
+COMPILER_ARCH=$(rustc -vV | sed -n 's|host: ||p')
+
+ARTIFACT_NAME=duskc-$COMPILER_ARCH.zip
+ARTIFACT_URL=$RELEASES_URL/$COMPILER_VERSION/$ARTIFACT_NAME
+
+ARTIFACT_DIR=$PWD/target/dusk/$COMPILER_VERSION
+ARTIFACT_PATH=$ARTIFACT_DIR/$ARTIFACT_NAME
+
+# If the artifact doesn't already exist in the target directory, download it,
+# otherwise skip.
+if [ ! -f "$ARTIFACT_PATH" ]; then
+    echo "Downloading compiler version $COMPILER_VERSION"
+    mkdir -p "$ARTIFACT_DIR"
+    curl -L "$ARTIFACT_URL" -o "$ARTIFACT_PATH"
+fi
+
+# Unzip the artifact, if it isn't already unzipped
+UNZIPPED_DIR=$ARTIFACT_DIR/unzipped
+
+if [ ! -d "$UNZIPPED_DIR" ]; then
+    echo "Extracting compiler..."
+    mkdir -p "$UNZIPPED_DIR"
+    unzip "$ARTIFACT_PATH" -d "$UNZIPPED_DIR" >> /dev/null
+    # We don't require the source of the compiler itself
+    rm "$UNZIPPED_DIR/rustc-nightly-src.tar.gz"
+fi
+
+# Extract the tarballs, if they aren't already extracted
+EXTRACTED_DIR=$ARTIFACT_DIR/extracted
+
+if [ ! -d "$EXTRACTED_DIR" ]; then
+    mkdir -p "$EXTRACTED_DIR"
+    tarballs=$(find "$UNZIPPED_DIR" -name '*.tar.gz')
+    for tarball in $tarballs; do
+        tar -xzf "$tarball" -C "$EXTRACTED_DIR" --strip-components=2 &
+    done
+    wait
+    # We don't require the, clearly clobbered at this point, file manifest
+    rm "$EXTRACTED_DIR/manifest.in"
+fi
+
+# Ensure that the extracted compiler is symlinked in the toolchain directory
+TOOLCHAIN_DIR=$HOME/.rustup/toolchains
+TOOLCHAIN_LINK=$TOOLCHAIN_DIR/dusk
+
+rm -f "$TOOLCHAIN_LINK"
+ln -s "$EXTRACTED_DIR" "$TOOLCHAIN_LINK"