Add BUILD_WRAP_ALLOW environment variable

README.md

@@ -20,6 +20,8 @@ Installing `build-wrap` requires two steps:
 
 ## Environment variables that `build-wrap` reads
 
+- `BUILD_WRAP_ALLOW`: When set to a value other than `0`, `build-wrap` uses the following weakened strategy. If a running a build script under `BUILD_WRAP_CMD` fails, report the failure and rerun the build script normally.
+
 - `BUILD_WRAP_CMD`: Command used to execute a build script. Linux default:
 
   ```sh

src/util/common.rs

@@ -36,8 +36,11 @@ pub fn exec_forwarding_output(mut command: Command, failure_is_error: bool) -> R
     std::io::stdout().flush()?;
     std::io::stderr().flush()?;
 
-    if failure_is_error {
-        ensure!(output.status.success(), "command failed: {command:?}");
+    if !output.status.success() {
+        if failure_is_error {
+            bail!("command failed: {command:?}");
+        }
+        eprintln!("command failed: {command:?}");
     }
 
     Ok(output)
@@ -65,9 +68,19 @@ fn unpack_and_exec(bytes: &[u8]) -> Result<()> {
     // They will cause the wrapped build script to be rerun, however.
     let expanded_args = split_and_expand(&temp_path)?;
 
+    let allow_enabled = enabled("BUILD_WRAP_ALLOW");
+
     let mut command = Command::new(&expanded_args[0]);
     command.args(&expanded_args[1..]);
-    let _: Output = exec_forwarding_output(command, true)?;
+    let output = exec_forwarding_output(command, !allow_enabled)?;
+
+    // smoelius: We should arrive at this `if` with `!output.status.success()` only when
+    // `BUILD_WRAP_ALLOW` is enabled.
+    if !output.status.success() {
+        debug_assert!(allow_enabled);
+        let command = Command::new(&temp_path);
+        let _: Output = exec_forwarding_output(command, true)?;
+    }
 
     drop(temp_path);
 
@@ -227,3 +240,7 @@ fn var(key: &str) -> Result<String, env::VarError> {
 
     env::var(key)
 }
+
+fn enabled(name: &str) -> bool {
+    env::var(name).map_or(false, |value| value != "0")
+}

tests/allow.rs

@@ -0,0 +1,20 @@
+pub mod util;
+
+#[test]
+fn allow() {
+    let temp_package = util::temp_package("tests/cases/ping.rs").unwrap();
+
+    for allow in [false, true] {
+        let mut command = util::build_with_build_wrap();
+        if allow {
+            command.env("BUILD_WRAP_ALLOW", "1");
+        }
+        command.current_dir(&temp_package);
+
+        let output = util::exec_forwarding_output(command, false).unwrap();
+        // smoelius: The command should succeed precisely when `BUILD_SCRIPT_ALLOW` is enabled.
+        assert_eq!(allow, output.status.success());
+        let stderr = std::str::from_utf8(&output.stderr).unwrap();
+        assert!(stderr.contains("command failed"));
+    }
+}