truncation fix and other drifts2

common/src/system_column.rs

@@ -45,6 +45,34 @@ pub const TRAILING_SYSTEM_COLUMNS: [SystemColumn; 1] = [SystemColumn {
 pub const ACCOUNT_REFERENCE_COLUMN: &str = "account_id";
 pub const ACCOUNT_API_COLUMN: &str = "account";
 
+/// The longest name any system column carries physically.
+///
+/// Anything that names a database object after a column has to reserve room
+/// for the widest name it could be given, and a user column's ordinal is far
+/// shorter than these. The bound is computed from the declarations above
+/// rather than picked by hand, so adding a system column moves it.
+///
+/// [`ACCOUNT_API_COLUMN`] is deliberately absent: it is an API spelling, never
+/// a physical column, so nothing is ever named after it.
+pub const LONGEST_SYSTEM_COLUMN_NAME: usize = longest_system_column_name();
+
+const fn longest_system_column_name() -> usize {
+    const fn longest_of(columns: &[SystemColumn], mut longest: usize) -> usize {
+        let mut index = 0;
+        while index < columns.len() {
+            let length = columns[index].name.len();
+            if length > longest {
+                longest = length;
+            }
+            index += 1;
+        }
+        longest
+    }
+
+    let longest = longest_of(&LEADING_SYSTEM_COLUMNS, ACCOUNT_REFERENCE_COLUMN.len());
+    longest_of(&TRAILING_SYSTEM_COLUMNS, longest)
+}
+
 /// Every system column name, whether or not the column is on a given table.
 ///
 /// A name is reserved for all tables even when only some tables carry the
@@ -75,8 +103,8 @@ pub fn system_column_name_list() -> String {
 #[cfg(test)]
 mod tests {
     use super::{
-        ACCOUNT_API_COLUMN, ACCOUNT_REFERENCE_COLUMN, is_system_column, system_column_name_list,
-        system_column_names,
+        ACCOUNT_API_COLUMN, ACCOUNT_REFERENCE_COLUMN, LONGEST_SYSTEM_COLUMN_NAME, is_system_column,
+        system_column_name_list, system_column_names,
     };
 
     #[test]
@@ -98,6 +126,20 @@ mod tests {
         assert!(!is_system_column("column_1"));
     }
 
+    /// The const derivation walks the arrays directly, so this walks the
+    /// public iterator instead. A system column declared somewhere the const
+    /// function does not reach shows up here as a disagreement rather than as
+    /// a truncated index name much later.
+    #[test]
+    fn the_longest_name_bound_covers_every_system_column() {
+        let longest = system_column_names()
+            .map(str::len)
+            .max()
+            .expect("there is always at least one system column");
+
+        assert_eq!(longest, LONGEST_SYSTEM_COLUMN_NAME);
+    }
+
     #[test]
     fn the_name_list_reads_as_a_sentence_fragment() {
         assert_eq!(