The year 0 will now render as 1BC for CSL

CSL year formatting will now use only a single code path. This code has been fixed to treat the year zero correctly. Unlike what has been suggested in #185, AD continues to be used as a postfix to comply with https://docs.citationstyles.org/en/stable/specification.html?#ad-and-bc

Fixes #185

src/csl/mod.rs

@@ -633,19 +633,9 @@ fn date_replacement<T: EntryLike>(
 
     ElemChildren(vec![ElemChild::Text(Formatted {
         text: if let Some(date) = date {
-            format!(
-                "{}{}",
-                if date.year > 0 { date.year } else { date.year.abs() + 1 },
-                if date.year < 1000 {
-                    if date.year < 0 {
-                        "BC"
-                    } else {
-                        "AD"
-                    }
-                } else {
-                    ""
-                }
-            )
+            let mut s = String::with_capacity(4);
+            write_year(date.year, false, &mut s).unwrap();
+            s
         } else if let Some(no_date) = ctx
             .ctx(entry, cite_props.clone(), locale, term_locale, false)
             .term(Term::Other(OtherTerm::NoDate), TermForm::default(), false)
@@ -658,6 +648,33 @@ fn date_replacement<T: EntryLike>(
     })])
 }
 
+pub fn write_year<W: std::fmt::Write>(
+    year: i32,
+    short: bool,
+    w: &mut W,
+) -> std::fmt::Result {
+    if short && year >= 1000 {
+        return write!(w, "{:02}", year % 100);
+    }
+
+    write!(
+        w,
+        "{}{}",
+        if year > 0 { year } else { year.abs() + 1 },
+        if year < 1000 {
+            if year <= 0 {
+                "BC"
+            } else {
+                // AD is used as a postfix, see
+                // https://docs.citationstyles.org/en/stable/specification.html?#ad-and-bc
+                "AD"
+            }
+        } else {
+            ""
+        }
+    )
+}
+
 fn last_purpose_render<T: EntryLike + Debug>(
     ctx: &StyleContext<'_>,
     item: &SpeculativeItemRender<T>,
@@ -2887,4 +2904,22 @@ mod tests {
             // }
         }
     }
+
+    #[test]
+    fn low_year_test() {
+        let yield_year = |year, short| {
+            let mut s = String::new();
+            write_year(year, short, &mut s).unwrap();
+            s
+        };
+
+        assert_eq!(yield_year(2021, false), "2021");
+        assert_eq!(yield_year(2021, true), "21");
+        assert_eq!(yield_year(0, false), "1BC");
+        assert_eq!(yield_year(-1, false), "2BC");
+        assert_eq!(yield_year(1, false), "1AD");
+        assert_eq!(yield_year(0, true), "1BC");
+        assert_eq!(yield_year(-1, true), "2BC");
+        assert_eq!(yield_year(1, true), "1AD");
+    }
 }

src/csl/rendering/mod.rs

@@ -20,7 +20,7 @@ use crate::types::{ChunkedString, Date, MaybeTyped, Numeric};
 use crate::PageRanges;
 
 use super::taxonomy::EntryLike;
-use super::{Context, ElemMeta, IbidState, SpecialForm, UsageInfo};
+use super::{write_year, Context, ElemMeta, IbidState, SpecialForm, UsageInfo};
 
 pub mod names;
 
@@ -769,17 +769,8 @@ fn render_date_part<T: EntryLike>(
                     write!(ctx, "{}", val).unwrap();
                 }
             }
-            DateStrongAnyForm::Year(LongShortForm::Short) => {
-                write!(ctx, "{:02}", (val % 100).abs()).unwrap();
-            }
-            DateStrongAnyForm::Year(LongShortForm::Long) => {
-                write!(ctx, "{}", val.abs()).unwrap();
-            }
-        }
-
-        if let DateStrongAnyForm::Year(_) = form {
-            if date.year < 1000 {
-                ctx.push_str(if date.year < 0 { "BC" } else { "AD" });
+            DateStrongAnyForm::Year(brevity) => {
+                write_year(val, brevity == LongShortForm::Short, ctx).unwrap();
             }
         }
     }