Introduce an option for disabling the automatic resolver in FileSourceFile

src/file/mod.rs

@@ -55,6 +55,20 @@ impl File<source::file::FileSourceFile> {
             source: source::file::FileSourceFile::new(name.into()),
         }
     }
+
+    /// Given the full name of a file, will use it only if with the exact name without
+    /// any attempt to locate another file. It will analyze the extension if the property
+    /// format isn't setted but without using file with a different fullname.
+    pub fn with_exact_name(name: &str) -> Self {
+        Self::with_name(name).exact(true)
+    }
+
+    /// If enabeld, and a file with the exact name is not found,
+    /// will not attempt to locate a file based on the format property.
+    pub fn exact(mut self, flag: bool) -> Self {
+        self.source.disable_file_resolve(flag);
+        self
+    }
 }
 
 impl<'a> From<&'a Path> for File<source::file::FileSourceFile> {

src/file/source/file.rs

@@ -17,11 +17,18 @@ use source::Source;
 pub struct FileSourceFile {
     /// Path of configuration file
     name: PathBuf,
+
+    /// Raise error if the exact filename is not found
+    disable_file_resolve: bool,
 }
 
 impl FileSourceFile {
     pub fn new(name: PathBuf) -> FileSourceFile {
-        FileSourceFile { name: name }
+        FileSourceFile { name: name, disable_file_resolve: false }
+    }
+
+    pub fn disable_file_resolve(&mut self, flag: bool) {
+        self.disable_file_resolve = flag;
     }
 
     fn find_file(
@@ -50,31 +57,33 @@ impl FileSourceFile {
                         io::ErrorKind::NotFound,
                         format!(
                             "configuration file \"{}\" is not of a registered file format",
-                            filename.to_string_lossy()
+                            self.name.to_string_lossy()
                         ),
                     )))
                 }
             };
         }
 
-        match format_hint {
-            Some(format) => for ext in format.extensions() {
-                filename.set_extension(ext);
-
-                if filename.is_file() {
-                    return Ok((filename, format));
-                }
-            },
-
-            None => for (format, extensions) in ALL_EXTENSIONS.iter() {
-                for ext in format.extensions() {
+        if !self.disable_file_resolve {
+            match format_hint {
+                Some(format) => for ext in format.extensions() {
                     filename.set_extension(ext);
 
                     if filename.is_file() {
-                        return Ok((filename, *format));
+                        return Ok((filename, format));
                     }
-                }
-            },
+                },
+
+                None => for (format, extensions) in ALL_EXTENSIONS.iter() {
+                    for ext in format.extensions() {
+                        filename.set_extension(ext);
+
+                        if filename.is_file() {
+                            return Ok((filename, *format));
+                        }
+                    }
+                },
+            }
         }
 
         Err(Box::new(io::Error::new(

tests/Settings.wrongextension

@@ -0,0 +1,8 @@
+debug = false
+production = true
+
+[place]
+rating = 4.9
+
+[place.creator]
+name = "Somebody New"

tests/file.rs

@@ -24,6 +24,40 @@ fn test_file_required_not_found() {
     );
 }
 
+#[test]
+fn test_file_exact_not_exist() {
+    let mut c = Config::default();
+    let res = c.merge(File::with_exact_name("tests/Settings.wrong"));
+
+    assert!(res.is_err());
+    assert_eq!(
+        res.unwrap_err().to_string(),
+        "configuration file \"tests/Settings.wrong\" not found".to_string()
+    );
+}
+
+#[test]
+fn test_file_exact_exist_invalid_extension() {
+    let mut c = Config::default();
+    let res = c.merge(File::with_exact_name("tests/Settings.wrongextension"));
+
+    assert!(res.is_err());
+    assert_eq!(
+        res.unwrap_err().to_string(),
+        "configuration file \"tests/Settings.wrongextension\" is not of a registered file format".to_string()
+    );
+}
+
+#[test]
+fn test_file_exact_explicit_format() {
+    let mut c = Config::default();
+    c.merge(File::new("tests/Settings.wrongextension", FileFormat::Toml).exact(true))
+        .unwrap();
+
+    assert_eq!(c.get("debug").ok(), Some(false));
+    assert_eq!(c.get("production").ok(), Some(true));
+}
+
 #[test]
 fn test_file_auto() {
     let mut c = Config::default();