Show multiple clippy.toml warnings with sess.warn instead of eprintln!

clippy_lints/src/lib.rs

@@ -348,13 +348,17 @@ pub fn register_pre_expansion_lints(store: &mut rustc_lint::LintStore, sess: &Se
 }
 
 #[doc(hidden)]
-pub fn read_conf(sess: &Session, path: &io::Result<Option<PathBuf>>) -> Conf {
+pub fn read_conf(sess: &Session, path: &io::Result<(Option<PathBuf>, Vec<String>)>) -> Conf {
+    if let Ok((_, warnings)) = path {
+        for warning in warnings {
+            sess.warn(warning);
+        }
+    }
     let file_name = match path {
-        Ok(Some(path)) => path,
-        Ok(None) => return Conf::default(),
+        Ok((Some(path), _)) => path,
+        Ok((None, _)) => return Conf::default(),
         Err(error) => {
-            sess.struct_err(format!("error finding Clippy's configuration file: {error}"))
-                .emit();
+            sess.err(format!("error finding Clippy's configuration file: {error}"));
             return Conf::default();
         },
     };

clippy_lints/src/utils/conf.rs

@@ -470,7 +470,7 @@ define_Conf! {
 /// # Errors
 ///
 /// Returns any unexpected filesystem error encountered when searching for the config file
-pub fn lookup_conf_file() -> io::Result<Option<PathBuf>> {
+pub fn lookup_conf_file() -> io::Result<(Option<PathBuf>, Vec<String>)> {
     /// Possible filename to search for.
     const CONFIG_FILE_NAMES: [&str; 2] = [".clippy.toml", "clippy.toml"];
 
@@ -481,6 +481,7 @@ pub fn lookup_conf_file() -> io::Result<Option<PathBuf>> {
         .map_or_else(|| PathBuf::from("."), PathBuf::from);
 
     let mut found_config: Option<PathBuf> = None;
+    let mut warnings = vec![];
 
     loop {
         for config_file_name in &CONFIG_FILE_NAMES {
@@ -491,12 +492,12 @@ pub fn lookup_conf_file() -> io::Result<Option<PathBuf>> {
                     Ok(md) if md.is_dir() => {},
                     Ok(_) => {
                         // warn if we happen to find two config files #8323
-                        if let Some(ref found_config_) = found_config {
-                            eprintln!(
-                                "Using config file `{}`\nWarning: `{}` will be ignored.",
-                                found_config_.display(),
-                                config_file.display(),
-                            );
+                        if let Some(ref found_config) = found_config {
+                            warnings.push(format!(
+                                "using config file `{}`, `{}` will be ignored",
+                                found_config.display(),
+                                config_file.display()
+                            ));
                         } else {
                             found_config = Some(config_file);
                         }
@@ -506,12 +507,12 @@ pub fn lookup_conf_file() -> io::Result<Option<PathBuf>> {
         }
 
         if found_config.is_some() {
-            return Ok(found_config);
+            return Ok((found_config, warnings));
         }
 
         // If the current directory has no parent, we're done searching.
         if !current.pop() {
-            return Ok(None);
+            return Ok((None, warnings));
         }
     }
 }

src/driver.rs

@@ -130,7 +130,7 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
     #[allow(rustc::bad_opt_access)]
     fn config(&mut self, config: &mut interface::Config) {
         let conf_path = clippy_lints::lookup_conf_file();
-        let conf_path_string = if let Ok(Some(path)) = &conf_path {
+        let conf_path_string = if let Ok((Some(path), _)) = &conf_path {
             path.to_str().map(String::from)
         } else {
             None

tests/ui-cargo/multiple_config_files/warn/src/main.stderr

@@ -1,2 +1,4 @@
-Using config file `$SRC_DIR/.clippy.toml`
-Warning: `$SRC_DIR/clippy.toml` will be ignored.
+warning: using config file `$SRC_DIR/.clippy.toml`, `$SRC_DIR/clippy.toml` will be ignored
+
+warning: 1 warning emitted
+