Implement stderr via log.

jaq-std/src/lib.rs

@@ -617,13 +617,13 @@ fn debug<V: core::fmt::Display>() -> Filter<(RunPtr<V>, UpdatePtr<V>)> {
     ("debug", v(0), id_with!(|x| log::debug!("{}", x)))
 }
 
-#[cfg(feature = "std")]
+#[cfg(feature = "log")]
 fn stderr<V: ValT>() -> Filter<(RunPtr<V>, UpdatePtr<V>)> {
     fn eprint_raw<V: ValT>(v: &V) {
         if let Some(s) = v.as_str() {
-            std::eprint!("{}", s)
+            log::error!("{}", s)
         } else {
-            std::eprint!("{}", v)
+            log::error!("{}", v)
         }
     }
     ("stderr", v(0), id_with!(eprint_raw))

jaq/Cargo.toml

@@ -24,6 +24,7 @@ codesnake = { version = "0.2" }
 clap = { version = "4.0.0", features = ["derive"] }
 env_logger = { version = "0.10.0", default-features = false }
 hifijson = "0.2.0"
+log = { version = "0.4.17" }
 memmap2 = "0.9"
 mimalloc = { version = "0.1.29", default-features = false, optional = true }
 tempfile = "3.3.0"

jaq/src/main.rs

@@ -134,7 +134,10 @@ fn main() -> ExitCode {
     use env_logger::Env;
     env_logger::Builder::from_env(Env::default().filter_or("LOG", "debug"))
         // format debug messages such as `["DEBUG", [1, 2, 3]]`
-        .format(|buf, record| writeln!(buf, "[\"{}:\", {}]", record.level(), record.args()))
+        .format(|buf, record| match record.level() {
+            log::Level::Error => write!(buf, "{}", record.args()),
+            level => writeln!(buf, "[\"{}:\", {}]", level, record.args()),
+        })
         .init();
 
     let cli = Cli::parse();