Rewatch: log warnings to stderr, too

CHANGELOG.md

@@ -24,7 +24,7 @@
 #### :bug: Bug fix
 
 - Fix rewatch swallowing parse warnings (%todo). https://github.com/rescript-lang/rescript/pull/8135
-- Rewatch: log errors to `stderr`. https://github.com/rescript-lang/rescript/pull/8147
+- Rewatch: log errors and warnings to `stderr`. https://github.com/rescript-lang/rescript/pull/8147 https://github.com/rescript-lang/rescript/pull/8148
 
 #### :memo: Documentation
 

rewatch/src/build.rs

@@ -306,7 +306,7 @@ pub fn incremental_build(
         }
     }
     if helpers::contains_ascii_characters(&parse_warnings) {
-        println!("{}", &parse_warnings);
+        eprintln!("{}", &parse_warnings);
     }
 
     mark_modules_with_expired_deps_dirty(build_state);
@@ -371,7 +371,7 @@ pub fn incremental_build(
             }
         }
         if helpers::contains_ascii_characters(&compile_warnings) {
-            println!("{}", &compile_warnings);
+            eprintln!("{}", &compile_warnings);
         }
         if initial_build {
             log_config_warnings(build_state);
@@ -400,7 +400,7 @@ pub fn incremental_build(
         }
 
         if helpers::contains_ascii_characters(&compile_warnings) {
-            println!("{}", &compile_warnings);
+            eprintln!("{}", &compile_warnings);
         }
         if initial_build {
             log_config_warnings(build_state);
@@ -451,21 +451,21 @@ fn log_deprecated_config_field(package_name: &str, field_name: &str, new_field_n
         "The field '{field_name}' found in the package config of '{package_name}' is deprecated and will be removed in a future version.\n\
         Use '{new_field_name}' instead."
     );
-    println!("\n{}", style(warning).yellow());
+    eprintln!("\n{}", style(warning).yellow());
 }
 
 fn log_unsupported_config_field(package_name: &str, field_name: &str) {
     let warning = format!(
         "The field '{field_name}' found in the package config of '{package_name}' is not supported by ReScript 12's new build system."
     );
-    println!("\n{}", style(warning).yellow());
+    eprintln!("\n{}", style(warning).yellow());
 }
 
 fn log_unknown_config_field(package_name: &str, field_name: &str) {
     let warning = format!(
         "Unknown field '{field_name}' found in the package config of '{package_name}'. This option will be ignored."
     );
-    println!("\n{}", style(warning).yellow());
+    eprintln!("\n{}", style(warning).yellow());
 }
 
 // write build.ninja files in the packages after a non-incremental build

rewatch/src/main.rs

@@ -165,10 +165,9 @@ impl log::Log for SplitLogger {
     }
 
     fn log(&self, record: &log::Record) {
-        if record.level() == log::Level::Error {
-            self.stderr.log(record);
-        } else {
-            self.stdout.log(record);
+        match record.level() {
+            log::Level::Error | log::Level::Warn => self.stderr.log(record),
+            _ => self.stdout.log(record),
         }
     }
 

tests/build_tests/build_warn_as_error/input.js

@@ -8,7 +8,7 @@ const o1 = await execBuild();
 // biome-ignore lint/suspicious/noControlCharactersInRegex: strip ANSI color codes from output
 const stripAnsi = s => s.replace(/\x1b\[[0-9;]*m/g, "");
 
-const first_message = stripAnsi(o1.stdout)
+const first_message = stripAnsi(o1.stderr)
   .split("\n")
   .map(s => s.trim())
   .find(s => s === "Warning number 110");