fix: enforce a lower case letter at the beginning of the summary content

src/error.rs

@@ -18,6 +18,7 @@ pub enum ParseErrorKind {
     UnexpectedWhitespaceOrNewLine,
     MalformedScope,
     MalformedOrUnexpectedFooterSeparator,
+    DescriptionStartingWithUppercase,
     Other,
 }
 
@@ -39,6 +40,9 @@ impl AsRef<str> for ParseErrorKind {
                 "Either token separator (` #` or `: `) \
             \nis missing from the footer or a footer was not expected at this point"
             }
+            ParseErrorKind::DescriptionStartingWithUppercase => {
+                "Malformed commit description: message should start with a lowercase letter"
+            }
             ParseErrorKind::Other => "Parse error",
         }
     }
@@ -72,6 +76,8 @@ impl From<PestError<Rule>> for ParseError {
                     ParseErrorKind::MalformedScope
                 } else if positives.contains(&Rule::token_separator) {
                     ParseErrorKind::MalformedOrUnexpectedFooterSeparator
+                } else if positives.contains(&Rule::summary_content) {
+                    ParseErrorKind::DescriptionStartingWithUppercase
                 } else {
                     ParseErrorKind::Other
                 }

src/grammar.pest

@@ -1,4 +1,4 @@
-summary_content = { (!NEWLINE ~ ANY)+ }
+summary_content = { LOWERCASE ~ (!NEWLINE ~ ANY)+ }
 
 message = { SOI ~ summary ~ (blank_line* ~ (footers | (body ~ blank_line+ ~ footers) | body))? ~ EOI }
 

tests/specification.rs

@@ -535,3 +535,15 @@ fn should_parse_interactively_rebased_commit() {
         },
     );
 }
+
+#[test]
+fn description_with_sentence_case_should_fail() {
+    // Arrange
+    let commit_message = "feat: Toto va à la plage";
+
+    // Act
+    let parsed = parse(commit_message);
+
+    // Assert
+    assert_error(&parsed, ParseErrorKind::DescriptionStartingWithUppercase);
+}