Extract applying of newline style into own mod

1 files changed, 118 insertions, 0 deletions

diff --git a/src/formatting/newline_style.rs b/src/formatting/newline_style.rs
new file mode 100644
index 00000000000..3cf66f83ed6
--- /dev/null
+++ b/src/formatting/newline_style.rs
@@ -0,0 +1,118 @@
+use crate::NewlineStyle;
+
+impl NewlineStyle {
+    fn auto_detect(raw_input_text: &str) -> NewlineStyle {
+        if let Some(pos) = raw_input_text.find('\n') {
+            let pos = pos.saturating_sub(1);
+            if let Some('\r') = raw_input_text.chars().nth(pos) {
+                NewlineStyle::Windows
+            } else {
+                NewlineStyle::Unix
+            }
+        } else {
+            NewlineStyle::Native
+        }
+    }
+
+    fn native() -> NewlineStyle {
+        if cfg!(windows) {
+            NewlineStyle::Windows
+        } else {
+            NewlineStyle::Unix
+        }
+    }
+
+    /// Apply this newline style to the formatted text. When the style is set
+    /// to `Auto`, the `raw_input_text` is used to detect the existing line
+    /// endings.
+    ///
+    /// If the style is set to `Auto` and `raw_input_text` contains no
+    /// newlines, the `Native` style will be used.
+    pub(crate) fn apply(self, formatted_text: &mut String, raw_input_text: &str) {
+        use crate::NewlineStyle::*;
+        let mut style = self;
+        if style == Auto {
+            style = Self::auto_detect(raw_input_text);
+        }
+        if style == Native {
+            style = Self::native();
+        }
+        match style {
+            Windows => {
+                let mut transformed = String::with_capacity(2 * formatted_text.capacity());
+                for c in formatted_text.chars() {
+                    match c {
+                        '\n' => transformed.push_str("\r\n"),
+                        '\r' => continue,
+                        c => transformed.push(c),
+                    }
+                }
+                *formatted_text = transformed;
+            }
+            Unix => return,
+            Native => unreachable!("NewlineStyle::Native"),
+            Auto => unreachable!("NewlineStyle::Auto"),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_newline_style_auto_detect() {
+        let lf = "One\nTwo\nThree";
+        let crlf = "One\r\nTwo\r\nThree";
+        let none = "One Two Three";
+
+        assert_eq!(NewlineStyle::Unix, NewlineStyle::auto_detect(lf));
+        assert_eq!(NewlineStyle::Windows, NewlineStyle::auto_detect(crlf));
+        assert_eq!(NewlineStyle::Native, NewlineStyle::auto_detect(none));
+    }
+
+    #[test]
+    fn test_newline_style_auto_apply() {
+        let auto = NewlineStyle::Auto;
+
+        let formatted_text = "One\nTwo\nThree";
+        let raw_input_text = "One\nTwo\nThree";
+
+        let mut out = String::from(formatted_text);
+        auto.apply(&mut out, raw_input_text);
+        assert_eq!("One\nTwo\nThree", &out, "auto should detect 'lf'");
+
+        let formatted_text = "One\nTwo\nThree";
+        let raw_input_text = "One\r\nTwo\r\nThree";
+
+        let mut out = String::from(formatted_text);
+        auto.apply(&mut out, raw_input_text);
+        assert_eq!("One\r\nTwo\r\nThree", &out, "auto should detect 'crlf'");
+
+        #[cfg(not(windows))]
+        {
+            let formatted_text = "One\nTwo\nThree";
+            let raw_input_text = "One Two Three";
+
+            let mut out = String::from(formatted_text);
+            auto.apply(&mut out, raw_input_text);
+            assert_eq!(
+                "One\nTwo\nThree", &out,
+                "auto-native-unix should detect 'lf'"
+            );
+        }
+
+        #[cfg(windows)]
+        {
+            let formatted_text = "One\nTwo\nThree";
+            let raw_input_text = "One Two Three";
+
+            let mut out = String::from(formatted_text);
+            auto.apply(&mut out, raw_input_text);
+            assert_eq!(
+                "One\r\nTwo\r\nThree", &out,
+                "auto-native-windows should detect 'crlf'"
+            );
+        }
+    }
+}