feat: expand ClaML Modifier/ModifierClass into terminal 5th-digit codes

ICD-10-GM models the 4th/5th sub-digits of many groups (incl. all E10-E14
diabetes) via <Modifier>/<ModifierClass> referenced by ordered <ModifiedBy>
on the parent <Class>, not as nested <Class> elements. load() previously
returned nothing for codes like E11.90/E11.72/I10.91, so ~1.7k corpus
codes (incl. ~1.2k billable) fell back to the non-billable 3-digit root
and were silently dropped under --billable-only.

Collect per-Class ModifiedBy refs and all ModifierClass defs during the
existing single stream, then expand: cartesian product of the referenced
modifiers' ModifierClass codes in ModifiedBy order, concatenated verbatim
onto the parent code (E11 + .9 + 0 = E11.90), matching the Alpha-ID
corpus format exactly. Terminal leaves are billable (Para295/Para301=P);
description = parent label + each ModifierClass label joined by ' - ';
chapter/group/exotic/ifsg/content inherited from parent. Purely additive:
explicit <Class> entries always win. Generic over every modifier group.

Map size 12334 -> 17249 (+4915 synthesized).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/claml.rs

@@ -17,12 +17,40 @@ fn roman_to_padded(roman: &str) -> Option<String> {
     Some(format!("{n:02}"))
 }
 
+/// A `<ModifierClass>` definition: its `code` (appended verbatim to the parent
+/// ICD code, e.g. `.9` for a 4th digit or `0` for a 5th digit) and its
+/// preferred-rubric label (used to compose the synthesized description).
+#[derive(Default, Clone)]
+struct ModifierClassDef {
+    code: String,
+    label: String,
+}
+
+/// Records, for one `<Class kind="category">`, the ordered list of
+/// `<ModifiedBy code=…>` references so the modifier chain can be expanded
+/// after the whole document has been parsed.
+struct ModifiedByRefs {
+    parent_code: String,
+    refs: Vec<String>,
+}
+
 /// Stream-parse the ClaML XML into a map keyed by normalised ICD code.
 ///
 /// The file is flat: `<Class kind="chapter">` elements close before their
 /// associated `<Class kind="category">` siblings begin.  We therefore track
 /// the most-recently-seen chapter and assign it to every category that
 /// follows, until the next chapter appears.
+///
+/// In addition to the explicit `<Class kind="category">` entries, ICD-10-GM
+/// models many 4th/5th sub-digits (e.g. all of `E10`-`E14`) not as nested
+/// `<Class>` elements but via `<Modifier>` / `<ModifierClass>` referenced by
+/// one or more ordered `<ModifiedBy code=…>` on the parent `<Class>`.  After
+/// the streaming pass we expand those: for every category Class carrying
+/// `<ModifiedBy>` refs we take the cartesian product of the referenced
+/// modifiers' `<ModifierClass>` codes (in `<ModifiedBy>` order) and synthesize
+/// a terminal billable entry per leaf (`Para295`/`Para301` = `"P"`).  This is
+/// purely additive: a key already produced by an explicit `<Class>` always
+/// wins.
 pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
     let mut reader = Reader::from_file(path)
         .map_err(|e| AppError::Io(format!("{path}: {e}")))?;
@@ -40,6 +68,19 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
 
     let mut in_preferred = false;
 
+    // ---- Modifier-expansion bookkeeping -------------------------------------
+    // For each modifier code => ordered list of its ModifierClass definitions.
+    let mut modifier_classes: HashMap<String, Vec<ModifierClassDef>> = HashMap::new();
+    // ModifiedBy refs collected per category Class (in document order).
+    let mut modified_by: Vec<ModifiedByRefs> = Vec::new();
+    // Refs accumulating for the currently-open category Class.
+    let mut cur_refs: Vec<String> = Vec::new();
+    let mut cur_code = String::new();
+    // Currently-open <ModifierClass>, if any (these are NOT category Classes,
+    // so `cur` stays None and the normal description path is bypassed).
+    let mut cur_mc: Option<ModifierClassDef> = None;
+    let mut cur_mc_modifier = String::new();
+
     loop {
         match reader.read_event_into(&mut buf) {
             Err(e) => return Err(AppError::Parse(format!("claml: {e}"))),
@@ -65,6 +106,8 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
                             }
                             cur = None;
                         } else if cur_kind == "category" {
+                            cur_code = code.clone();
+                            cur_refs.clear();
                             let m = IcdMeta {
                                 code,
                                 chapter: current_chapter.clone(),
@@ -75,6 +118,34 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
                             cur = None;
                         }
                     }
+                    b"ModifierClass" => {
+                        let mut mc = ModifierClassDef::default();
+                        cur_mc_modifier.clear();
+                        for a in t.attributes().flatten() {
+                            match a.key.as_ref() {
+                                b"code" => mc.code = String::from_utf8_lossy(&a.value).into_owned(),
+                                b"modifier" => {
+                                    cur_mc_modifier =
+                                        String::from_utf8_lossy(&a.value).into_owned()
+                                }
+                                _ => {}
+                            }
+                        }
+                        cur_mc = Some(mc);
+                        cur = None;
+                    }
+                    b"ModifiedBy" => {
+                        // Only meaningful while a category Class is open.
+                        if cur.is_some() {
+                            for a in t.attributes().flatten() {
+                                if a.key.as_ref() == b"code" {
+                                    cur_refs.push(
+                                        String::from_utf8_lossy(&a.value).into_owned(),
+                                    );
+                                }
+                            }
+                        }
+                    }
                     b"SuperClass" => {
                         if let Some(m) = cur.as_mut() {
                             for a in t.attributes().flatten() {
@@ -125,9 +196,11 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
 
             Ok(Event::Text(txt)) => {
                 if in_preferred {
-                    if let Some(m) = cur.as_mut() {
                     let s = txt.unescape().unwrap_or_default();
+                    if let Some(m) = cur.as_mut() {
                         m.description.push_str(&s);
+                    } else if let Some(mc) = cur_mc.as_mut() {
+                        mc.label.push_str(&s);
                     }
                 }
             }
@@ -137,9 +210,26 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
                 b"Class" => {
                     if let Some(m) = cur.take() {
                         if !m.code.is_empty() {
+                            if !cur_refs.is_empty() {
+                                modified_by.push(ModifiedByRefs {
+                                    parent_code: cur_code.clone(),
+                                    refs: std::mem::take(&mut cur_refs),
+                                });
+                            }
                             map.insert(m.code.clone(), m);
                         }
                     }
+                    cur_refs.clear();
+                }
+                b"ModifierClass" => {
+                    if let Some(mc) = cur_mc.take() {
+                        if !cur_mc_modifier.is_empty() {
+                            modifier_classes
+                                .entry(std::mem::take(&mut cur_mc_modifier))
+                                .or_default()
+                                .push(mc);
+                        }
+                    }
                 }
                 _ => {}
             },
@@ -152,5 +242,115 @@ pub fn load(path: &str) -> Result<HashMap<String, IcdMeta>, AppError> {
     if map.is_empty() {
         return Err(AppError::Parse(format!("no ClaML categories in {path}")));
     }
+
+    expand_modifiers(&mut map, &modified_by, &modifier_classes);
+
     Ok(map)
 }
+
+/// Expand every category `<Class>` that carries `<ModifiedBy>` references into
+/// its terminal sub-digit leaves.
+///
+/// The chain is the Class's `<ModifiedBy>` codes in document order (4th digit
+/// first, then 5th, …); each ref resolves to that modifier's ordered list of
+/// `<ModifierClass>` definitions.  We take the cartesian product across the
+/// chain, concatenating each `<ModifierClass>` `code` verbatim onto the parent
+/// ICD code (e.g. `E11` + `.9` + `0` = `E11.90`, `I10.0` + `1` = `I10.01`),
+/// which exactly matches the Alpha-ID corpus code format.
+///
+/// Only the terminal leaf (every modifier in the chain applied) is emitted as
+/// a billable code (`Para295`/`Para301` = `"P"`); intermediate prefixes such as
+/// the bare 3-steller keep whatever the explicit `<Class>` said (typically
+/// `"V"`).  The description is the parent's preferred label followed by each
+/// `<ModifierClass>` label, joined by " - " (empty labels skipped).
+///
+/// Purely additive: a key already present (produced by an explicit `<Class>`)
+/// is never overwritten — explicit always wins.
+fn expand_modifiers(
+    map: &mut HashMap<String, IcdMeta>,
+    modified_by: &[ModifiedByRefs],
+    modifier_classes: &HashMap<String, Vec<ModifierClassDef>>,
+) {
+    for mb in modified_by {
+        // Resolve the chain: each ModifiedBy ref => that modifier's ordered
+        // ModifierClass list.  Skip the whole Class if any ref is unknown.
+        let mut chain: Vec<&Vec<ModifierClassDef>> = Vec::with_capacity(mb.refs.len());
+        let mut resolvable = true;
+        for r in &mb.refs {
+            match modifier_classes.get(r) {
+                Some(list) if !list.is_empty() => chain.push(list),
+                _ => {
+                    resolvable = false;
+                    break;
+                }
+            }
+        }
+        if !resolvable || chain.is_empty() {
+            continue;
+        }
+
+        // Inherit fields from the parent's explicit entry.
+        let parent = match map.get(&mb.parent_code) {
+            Some(p) => p,
+            None => continue,
+        };
+        let parent_label = parent.description.clone();
+        let parent_chapter = parent.chapter.clone();
+        let parent_group = parent.group.clone();
+        let parent_exotic = parent.exotic;
+        let parent_ifsg = parent.ifsg;
+        let parent_content = parent.content;
+
+        // Cartesian product over the chain, in ModifiedBy (digit) order.
+        // `acc` holds (concatenated-code-suffix, composed-label-tail) pairs.
+        let mut acc: Vec<(String, String)> = vec![(String::new(), String::new())];
+        for level in &chain {
+            let mut next: Vec<(String, String)> = Vec::with_capacity(acc.len() * level.len());
+            for (code_acc, label_acc) in &acc {
+                for mc in level.iter() {
+                    let code = format!("{code_acc}{}", mc.code);
+                    let label = if mc.label.trim().is_empty() {
+                        label_acc.clone()
+                    } else if label_acc.is_empty() {
+                        mc.label.trim().to_string()
+                    } else {
+                        format!("{label_acc} - {}", mc.label.trim())
+                    };
+                    next.push((code, label));
+                }
+            }
+            acc = next;
+        }
+
+        for (suffix, label_tail) in acc {
+            let key = format!("{}{suffix}", mb.parent_code);
+            // Additive only: never overwrite an explicit Class entry.
+            if map.contains_key(&key) {
+                continue;
+            }
+            let mut description = parent_label.clone();
+            if !label_tail.is_empty() {
+                if description.is_empty() {
+                    description = label_tail;
+                } else {
+                    description.push_str(" - ");
+                    description.push_str(&label_tail);
+                }
+            }
+            map.insert(
+                key.clone(),
+                IcdMeta {
+                    code: key,
+                    description,
+                    chapter: parent_chapter.clone(),
+                    group: parent_group.clone(),
+                    para295: "P".to_string(),
+                    para301: "P".to_string(),
+                    exotic: parent_exotic,
+                    ifsg: parent_ifsg,
+                    content: parent_content,
+                },
+            );
+        }
+    }
+}

tests/claml_modifier_tests.rs

@@ -0,0 +1,16 @@
+use alpha_id::claml;
+
+#[test]
+fn expands_diabetes_5th_digit_codes_as_billable() {
+    let map = claml::load("icd-claml/Klassifikationsdateien/icd10gm2026syst_claml_20250912.xml").unwrap();
+    let e1190 = map.get("E11.90").expect("E11.90 synthesized from ModifierClass");
+    assert_eq!(e1190.para295, "P", "terminal 5th-digit diabetes code must be billable");
+    assert!(e1190.description.to_lowercase().contains("diabetes"),
+        "composed description from parent + modifier labels: {:?}", e1190.description);
+    let e1172 = map.get("E11.72").expect("E11.72 synthesized");
+    assert_eq!(e1172.para295, "P");
+    let a010 = map.get("A01.0").expect("A01.0 explicit");
+    assert_eq!(a010.para295, "P");
+    assert!(a010.description.contains("Typhus abdominalis"));
+    assert_eq!(map.get("E11").expect("E11 root").para295, "V");
+}