Ensure that --error-format is only passed once to rustc

rls/src/build/cargo.rs

@@ -391,7 +391,11 @@ impl Executor for RlsExecutor {
         _on_stdout_line: &mut dyn FnMut(&str) -> CargoResult<()>,
         _on_stderr_line: &mut dyn FnMut(&str) -> CargoResult<()>,
     ) -> CargoResult<()> {
-        // Use JSON output so that we can parse the rustc output.
+        // Enforce JSON output so that we can parse the rustc output by
+        // stripping --error-format if it was specified (e.g. Cargo pipelined
+        // build)
+        let filtered_args = filter_arg(cargo_cmd.get_args(), "--error-format");
+        cargo_cmd.args_replace(&filtered_args);
         cargo_cmd.arg("--error-format=json");
         // Delete any stale data. We try and remove any json files with
         // the same crate name as Cargo would emit. This includes files
@@ -755,6 +759,27 @@ fn dedup_flags(flag_str: &str) -> String {
     result
 }
 
+/// Removes a selected flag of a `--flag=VALUE` or `--flag VALUE` shape from `args` (command line args for Rust).
+fn filter_arg(args: &[OsString], key: &str) -> Vec<String> {
+    let key_as_prefix = key.to_owned() + "=";
+    let mut ret = vec![];
+
+    let mut iter = args.iter();
+    while let Some(arg) = iter.next() {
+        let first = arg.to_str().unwrap();
+
+        if first == key {
+            iter.next();
+        } else if first.starts_with(&key_as_prefix) {
+            // no-op
+        } else {
+            ret.push(first.to_owned());
+        }
+    }
+
+    ret
+}
+
 /// Error wrapper that tries to figure out which manifest the cause best relates to in the project
 #[derive(Debug)]
 pub struct ManifestAwareError {
@@ -837,7 +862,7 @@ impl failure::Fail for ManifestAwareError {
 
 #[cfg(test)]
 mod test {
-    use super::dedup_flags;
+    use super::{dedup_flags, filter_arg};
 
     #[test]
     fn test_dedup_flags() {
@@ -870,4 +895,21 @@ mod test {
             ) == " -Clink-args=-fuse-ld=gold -Ctarget-cpu=native"
         );
     }
+
+    #[test]
+    fn test_filter_arg() {
+        use std::ffi::OsString;
+
+        fn args(input: &str) -> Vec<OsString> {
+            input.split_whitespace().map(OsString::from).collect()
+        }
+
+        assert!(filter_arg(&args("--error-format=json"), "--error-format").is_empty());
+        assert!(filter_arg(&args("--error-format json"), "--error-format").is_empty());
+        assert_eq!(filter_arg(&args("-a --error-format=json"), "--error-format"), ["-a"]);
+        assert_eq!(filter_arg(&args("-a --error-format json"), "--error-format"), ["-a"]);
+        assert_eq!(filter_arg(&args("-a --error-format=json -b"), "--error-format"), ["-a", "-b"]);
+        assert_eq!(filter_arg(&args("-a --error-format json -b"), "--error-format"), ["-a", "-b"]);
+        assert_eq!(filter_arg(&args("-a -b -x"), "--error-format"), ["-a", "-b", "-x"]);
+    }
 }