feat(config file): warn when multiple configs found

src/main.rs

@@ -10,11 +10,10 @@ use lexopt::prelude::*;
 use typstfmt_lib::{format, Config};
 
 const VERSION: &str = env!("TYPSTFMT_VERSION");
-// Dot file is only used once when reading existing config file, therefore there
-// is no need in creating a `const DOT_CONFIG_FILE_NAME`. And even if this
-// constant was created, we would have to duplicate the whole string slice,
-// because `format!(".{CONFIG_FILE_NAME}")` (non-const function) cannot be
-// applied to `const` (or `static`) values in Rust (1.72.1).
+// `DOT_CONFIG_FILE_NAME` is not created as a const due to the fact that we
+// would have to duplicate the whole string slice, because
+// `format!(".{CONFIG_FILE_NAME}")` (non-const function) cannot be applied to
+// `const` (or `static`) values in Rust (1.72.1).
 const CONFIG_FILE_NAME: &str = "typstfmt.toml";
 const HELP: &str = r#"Format Typst code
 
@@ -197,9 +196,17 @@ fn main() -> Result<(), lexopt::Error> {
 
     let config = {
         let open_config = |file_name| File::options().read(true).open(file_name);
-        if let Ok(mut f) =
-            open_config(CONFIG_FILE_NAME).or(open_config(&format!(".{CONFIG_FILE_NAME}")))
-        {
+        let config = open_config(CONFIG_FILE_NAME);
+        let dot_config_file_name = format!(".{CONFIG_FILE_NAME}");
+        let dot_config = open_config(&dot_config_file_name);
+        if config.is_ok() && dot_config.is_ok() {
+            eprintln!(
+                "Warning! Both \"{first}\" and \"{second}\" are present. Using \"{first}\".",
+                first = CONFIG_FILE_NAME,
+                second = dot_config_file_name
+            );
+        }
+        if let Ok(mut f) = config.or(dot_config) {
             let mut buf = String::default();
             f.read_to_string(&mut buf).unwrap_or_else(|err| {
                 panic!("Failed to read config file {CONFIG_FILE_NAME:?}: {err}")