pallet-contracts-fixtures: Only build RISCV when the feature is enabled (#2870)

This disables building the RISCV fixtures by default. They still require
a custom build rustc version. When there are actual tests for RISCV, the
feature can be enabled in CI. Also fixes some unwraps that assume again
that people are using rustup...

substrate/frame/contracts/fixtures/Cargo.toml

@@ -23,3 +23,7 @@ toml = "0.8.2"
 twox-hash = "1.6.3"
 polkavm-linker = "0.3.0"
 anyhow = "1.0.0"
+
+[features]
+# Enable experimental RISCV fixtures build
+riscv-experimental = []

substrate/frame/contracts/fixtures/build.rs

@@ -16,7 +16,7 @@
 // limitations under the License.
 
 //! Compile contracts to wasm and RISC-V binaries.
-use anyhow::{bail, format_err, Context, Result};
+use anyhow::{bail, Context, Result};
 use parity_wasm::elements::{deserialize_file, serialize_to_file, Internal};
 use std::{
 	env, fs,
@@ -91,6 +91,7 @@ impl Entry {
 	}
 
 	/// Return the name of the RISC-V polkavm file.
+	#[cfg(feature = "riscv-experimental")]
 	fn out_riscv_filename(&self) -> String {
 		format!("{}.polkavm", self.name())
 	}
@@ -231,6 +232,7 @@ fn post_process_wasm(input_path: &Path, output_path: &Path) -> Result<()> {
 }
 
 /// Build contracts for RISC-V.
+#[cfg(feature = "riscv-experimental")]
 fn invoke_riscv_build(current_dir: &Path) -> Result<()> {
 	let encoded_rustflags =
 		["-Crelocation-model=pie", "-Clink-arg=--emit-relocs", "-Clink-arg=-Tmemory.ld"]
@@ -241,10 +243,10 @@ fn invoke_riscv_build(current_dir: &Path) -> Result<()> {
 	let build_res = Command::new(env::var("CARGO")?)
 		.current_dir(current_dir)
 		.env_clear()
-		.env("PATH", env::var("PATH").unwrap())
+		.env("PATH", env::var("PATH").unwrap_or_default())
 		.env("CARGO_ENCODED_RUSTFLAGS", encoded_rustflags)
 		.env("RUSTUP_TOOLCHAIN", "rve-nightly")
-		.env("RUSTUP_HOME", env::var("RUSTUP_HOME").unwrap())
+		.env("RUSTUP_HOME", env::var("RUSTUP_HOME").unwrap_or_default())
 		.args(["build", "--release", "--target=riscv32em-unknown-none-elf"])
 		.output()
 		.expect("failed to execute process");
@@ -265,12 +267,13 @@ fn invoke_riscv_build(current_dir: &Path) -> Result<()> {
 	bail!("Failed to build contracts");
 }
 /// Post-process the compiled wasm contracts.
+#[cfg(feature = "riscv-experimental")]
 fn post_process_riscv(input_path: &Path, output_path: &Path) -> Result<()> {
 	let mut config = polkavm_linker::Config::default();
 	config.set_strip(true);
 	let orig = fs::read(input_path).with_context(|| format!("Failed to read {:?}", input_path))?;
 	let linked = polkavm_linker::program_from_elf(config, orig.as_ref())
-		.map_err(|err| format_err!("Failed to link polkavm program: {}", err))?;
+		.map_err(|err| anyhow::format_err!("Failed to link polkavm program: {}", err))?;
 	fs::write(output_path, linked.as_bytes()).map_err(Into::into)
 }
 
@@ -283,6 +286,7 @@ fn write_output(build_dir: &Path, out_dir: &Path, entries: Vec<Entry>) -> Result
 			&out_dir.join(&wasm_output),
 		)?;
 
+		#[cfg(feature = "riscv-experimental")]
 		post_process_riscv(
 			&build_dir.join("target/riscv32em-unknown-none-elf/release").join(entry.name()),
 			&out_dir.join(entry.out_riscv_filename()),
@@ -335,6 +339,8 @@ fn main() -> Result<()> {
 	)?;
 
 	invoke_wasm_build(tmp_dir_path)?;
+
+	#[cfg(feature = "riscv-experimental")]
 	invoke_riscv_build(tmp_dir_path)?;
 
 	write_output(tmp_dir_path, &out_dir, entries)?;