feat(Description): implement Description and tests

src/commit/types/description.rs

@@ -0,0 +1,376 @@
+use std::fmt::write;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[repr(transparent)]
+pub struct Description(String);
+
+impl Description {
+    pub const MAX_LENGTH: usize = 72;
+
+    /// Parse and validate a description string
+    ///
+    /// # Validation
+    /// - Trims leading/trailing whitespace
+    /// - Rejects empty or whitespace-only input
+    /// - Validates maximum length (72 chars after trim)
+    pub fn parse(value: impl Into<String>) -> Result<Self, DescriptionError> {
+        let value = value.into().trim().to_owned();
+        if value.is_empty() {
+            return Err(DescriptionError::Empty);
+        }
+        if value.len() > Self::MAX_LENGTH {
+            Err(DescriptionError::TooLong {
+                actual: value.len(),
+                max: Self::MAX_LENGTH,
+            })
+        } else {
+            Ok(Self(value))
+        }
+    }
+
+    /// Returns the inner string slice
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+
+    /// Returns the length in characters
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    /// Always returns false for a valid `Description`
+    /// (included for API completeness, but logically always false)
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+impl AsRef<str> for Description {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+impl std::fmt::Display for Description {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+
+#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
+pub enum DescriptionError {
+    #[error("Description cannot be empty")]
+    Empty,
+
+    #[error("Description too long ({actual} characters, maximum is {max})")]
+    TooLong { actual: usize, max: usize },
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Test that valid description is accepted
+    #[test]
+    fn valid_description_accepted() {
+        let result = Description::parse("add new feature");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add new feature");
+    }
+
+    /// Test that single character description is accepted
+    #[test]
+    fn single_character_description_accepted() {
+        let result = Description::parse("a");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "a");
+    }
+
+    /// Test that description with numbers is accepted
+    #[test]
+    fn description_with_numbers_accepted() {
+        let result = Description::parse("fix issue #123");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "fix issue #123");
+    }
+
+    /// Test that description with special characters is accepted
+    #[test]
+    fn description_with_special_chars_accepted() {
+        let result = Description::parse("add @decorator support (beta)");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add @decorator support (beta)");
+    }
+
+    /// Test that description with punctuation is accepted
+    #[test]
+    fn description_with_punctuation_accepted() {
+        let result = Description::parse("fix: handle edge case!");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "fix: handle edge case!");
+    }
+
+    /// Test that empty string is rejected with DescriptionError::Empty
+    #[test]
+    fn empty_string_rejected() {
+        let result = Description::parse("");
+        assert!(result.is_err());
+        assert_eq!(result.unwrap_err(), DescriptionError::Empty);
+    }
+
+    /// Test that whitespace-only is rejected with DescriptionError::Empty
+    #[test]
+    fn whitespace_only_rejected() {
+        let result = Description::parse("   ");
+        assert!(result.is_err());
+        assert_eq!(result.unwrap_err(), DescriptionError::Empty);
+    }
+
+    /// Test that tabs-only is rejected
+    #[test]
+    fn tabs_only_rejected() {
+        let result = Description::parse("\t\t");
+        assert!(result.is_err());
+        assert_eq!(result.unwrap_err(), DescriptionError::Empty);
+    }
+
+    /// Test that mixed whitespace is rejected
+    #[test]
+    fn mixed_whitespace_rejected() {
+        let result = Description::parse("  \t  \n  ");
+        assert!(result.is_err());
+        assert_eq!(result.unwrap_err(), DescriptionError::Empty);
+    }
+
+    /// Test that newline-only is rejected
+    #[test]
+    fn newline_only_rejected() {
+        let result = Description::parse("\n");
+        assert!(result.is_err());
+        assert_eq!(result.unwrap_err(), DescriptionError::Empty);
+    }
+
+    /// Test that leading whitespace is trimmed
+    #[test]
+    fn leading_whitespace_trimmed() {
+        let result = Description::parse("  add feature");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add feature");
+    }
+
+    /// Test that trailing whitespace is trimmed
+    #[test]
+    fn trailing_whitespace_trimmed() {
+        let result = Description::parse("add feature  ");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add feature");
+    }
+
+    /// Test that both leading and trailing whitespace is trimmed
+    #[test]
+    fn leading_and_trailing_whitespace_trimmed() {
+        let result = Description::parse("  add feature  ");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add feature");
+    }
+
+    /// Test that internal whitespace is preserved
+    #[test]
+    fn internal_whitespace_preserved() {
+        let result = Description::parse("add   multiple   spaces");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str(), "add   multiple   spaces");
+    }
+
+    /// Test that exactly 72 characters is accepted (boundary)
+    #[test]
+    fn seventy_two_characters_accepted() {
+        let desc_72 = "a".repeat(72);
+        let result = Description::parse(&desc_72);
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str().len(), 72);
+    }
+
+    /// Test that 73 characters is rejected
+    #[test]
+    fn seventy_three_characters_rejected() {
+        let desc_73 = "a".repeat(73);
+        let result = Description::parse(&desc_73);
+        assert!(result.is_err());
+        assert_eq!(
+            result.unwrap_err(),
+            DescriptionError::TooLong {
+                actual: 73,
+                max: 72
+            }
+        );
+    }
+
+    /// Test that 100 characters is rejected
+    #[test]
+    fn hundred_characters_rejected() {
+        let desc_100 = "a".repeat(100);
+        let result = Description::parse(&desc_100);
+        assert!(result.is_err());
+        assert_eq!(
+            result.unwrap_err(),
+            DescriptionError::TooLong {
+                actual: 100,
+                max: 72
+            }
+        );
+    }
+
+    /// Test that length is checked after trimming
+    #[test]
+    fn length_checked_after_trimming() {
+        // 72 chars + leading/trailing spaces = should be valid after trim
+        let desc_with_spaces = format!("  {}  ", "a".repeat(72));
+        let result = Description::parse(&desc_with_spaces);
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str().len(), 72);
+    }
+
+    /// Test that 50 characters is accepted without issue
+    #[test]
+    fn fifty_characters_accepted() {
+        let desc_50 = "a".repeat(50);
+        let result = Description::parse(&desc_50);
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().as_str().len(), 50);
+    }
+
+    /// Test MAX_LENGTH constant is 72
+    #[test]
+    fn max_length_constant_is_72() {
+        assert_eq!(Description::MAX_LENGTH, 72);
+    }
+
+    /// Test as_str() returns inner string
+    #[test]
+    fn as_str_returns_inner_string() {
+        let desc = Description::parse("my description").unwrap();
+        assert_eq!(desc.as_str(), "my description");
+    }
+
+    /// Test len() returns correct length
+    #[test]
+    fn len_returns_correct_length() {
+        let desc = Description::parse("hello").unwrap();
+        assert_eq!(desc.len(), 5);
+    }
+
+    /// Test is_empty() always returns false for valid Description
+    #[test]
+    fn is_empty_always_false_for_valid() {
+        let desc = Description::parse("x").unwrap();
+        assert!(!desc.is_empty());
+    }
+
+    /// Test Display trait implementation
+    #[test]
+    fn display_outputs_inner_string() {
+        let desc = Description::parse("add feature").unwrap();
+        assert_eq!(format!("{}", desc), "add feature");
+    }
+
+    /// Test Clone trait
+    #[test]
+    fn description_is_cloneable() {
+        let original = Description::parse("add feature").unwrap();
+        let cloned = original.clone();
+        assert_eq!(original, cloned);
+    }
+
+    /// Test PartialEq trait
+    #[test]
+    fn description_equality() {
+        let desc1 = Description::parse("add feature").unwrap();
+        let desc2 = Description::parse("add feature").unwrap();
+        let desc3 = Description::parse("fix bug").unwrap();
+        assert_eq!(desc1, desc2);
+        assert_ne!(desc1, desc3);
+    }
+
+    /// Test Debug trait
+    #[test]
+    fn description_has_debug() {
+        let desc = Description::parse("add feature").unwrap();
+        let debug_output = format!("{:?}", desc);
+        assert!(debug_output.contains("Description"));
+        assert!(debug_output.contains("add feature"));
+    }
+
+    /// Test AsRef<str> trait
+    #[test]
+    fn description_as_ref_str() {
+        let desc = Description::parse("add feature").unwrap();
+        let s: &str = desc.as_ref();
+        assert_eq!(s, "add feature");
+    }
+
+    /// Test DescriptionError::Empty displays correctly
+    #[test]
+    fn empty_error_display() {
+        let err = DescriptionError::Empty;
+        let msg = format!("{}", err);
+        assert!(msg.contains("cannot be empty"));
+    }
+
+    /// Test DescriptionError::TooLong displays correctly
+    #[test]
+    fn too_long_error_display() {
+        let err = DescriptionError::TooLong {
+            actual: 73,
+            max: 72,
+        };
+        let msg = format!("{}", err);
+        assert!(msg.contains("too long"));
+        assert!(msg.contains("73"));
+        assert!(msg.contains("72"));
+    }
+
+    /// Test description with only whitespace after trim becomes empty
+    #[test]
+    fn whitespace_after_trim_is_empty() {
+        // Ensure various whitespace combinations all result in Empty error
+        let whitespace_variants = [" ", "  ", "\t", "\n", "\r\n", " \t \n "];
+        for ws in whitespace_variants {
+            let result = Description::parse(ws);
+            assert!(result.is_err(), "Expected error for whitespace: {:?}", ws);
+            assert_eq!(
+                result.unwrap_err(),
+                DescriptionError::Empty,
+                "Expected Empty error for whitespace: {:?}",
+                ws
+            );
+        }
+    }
+
+    /// Test description at exact boundary after trimming
+    #[test]
+    fn boundary_length_after_trim() {
+        // 72 chars + 2 spaces on each side = 76 chars total, but 72 after trim
+        let desc = format!("  {}  ", "x".repeat(72));
+        let result = Description::parse(&desc);
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap().len(), 72);
+    }
+
+    /// Test description just over boundary after trimming
+    #[test]
+    fn over_boundary_after_trim() {
+        // 73 chars + spaces = should fail even after trim
+        let desc = format!("  {}  ", "x".repeat(73));
+        let result = Description::parse(&desc);
+        assert!(result.is_err());
+        assert_eq!(
+            result.unwrap_err(),
+            DescriptionError::TooLong {
+                actual: 73,
+                max: 72
+            }
+        );
+    }
+}

src/commit/types/mod.rs

@@ -3,3 +3,6 @@ pub use commit_type::CommitType;
 
 mod scope;
 pub use scope::{Scope, ScopeError};
+
+mod description;
+pub use description::{Description, DescriptionError};

src/commit/types/scope.rs

@@ -39,7 +39,7 @@ impl Scope {
 
     /// Returns true if the scope is empty
     pub fn is_empty(&self) -> bool {
-        self.0 == String::new()
+        self.0.is_empty()
     }
 
     /// Returns the inner string slice