chore: add dropped question to reports

src/analysis/diagnostic.rs

@@ -172,6 +172,12 @@ pub struct StudentDiagnostic {
     /// One row per question, with no question in it.
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub questions: Vec<QuestionRow>,
+    /// Questions dropped from scoring, in number order.
+    ///
+    /// Reported separately from the question rows so the document can say once,
+    /// in prose, why the denominator is smaller than the paper was.
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    pub dropped_questions: Vec<u32>,
     /// Which lectures to go back to, the one that would repay the most time
     /// first.
     #[serde(skip_serializing_if = "Vec::is_empty")]
@@ -320,6 +326,13 @@ pub struct QuestionRow {
     /// Whether it was a bonus question.
     #[serde(skip_serializing_if = "std::ops::Not::not")]
     pub bonus: bool,
+    /// Whether it was dropped from scoring after the fact.
+    ///
+    /// A dropped question still appears in the map, because the student has the
+    /// paper in front of them and will look for it. What it must not do is
+    /// appear as an error they made.
+    #[serde(skip_serializing_if = "std::ops::Not::not")]
+    pub dropped: bool,
     /// Whether the student left it blank.
     pub blank: bool,
     /// The share of the class that answered it correctly, when comparison is on.
@@ -530,6 +543,14 @@ pub fn student(
         Vec::new()
     };
 
+    let mut dropped_questions: Vec<u32> = rows
+        .iter()
+        .filter(|r| r.dropped)
+        .map(|r| r.item_number)
+        .collect();
+    dropped_questions.sort_unstable();
+    dropped_questions.dedup();
+
     // Built from the response rows rather than from `questions`, so a report with
     // `--no-questions` still says where to go back to; it just does not name the
     // question numbers.
@@ -573,6 +594,7 @@ pub fn student(
         strengths,
         focus,
         questions,
+        dropped_questions,
         review_lectures,
         study,
     }
@@ -591,7 +613,10 @@ fn question_row(
     opts: &Options,
 ) -> QuestionRow {
     let blank = row.selected.is_empty() && row.eliminated.is_empty();
-    let missed = row.credit < 0.999;
+    // A dropped question cannot be missed. Without `counts()` here, a question
+    // thrown out after the exam still collects per-option feedback explaining an
+    // error the student is no longer being charged for.
+    let missed = row.credit < 0.999 && row.counts();
     let mut feedback = None;
     let mut hint = None;
     let mut misconception = None;
@@ -673,6 +698,7 @@ fn question_row(
         correct: row.correct,
         credit: row.credit,
         bonus: row.bonus,
+        dropped: row.dropped,
         blank,
         class_rate: opts
             .comparison
@@ -926,6 +952,11 @@ pub struct CohortDiagnostic {
     pub lectures: Vec<CohortLectureRow>,
     /// Per-question statistics.
     pub questions: Vec<CohortQuestionRow>,
+    /// Questions dropped from scoring, which are therefore absent from every
+    /// table above. Recorded so the report says why rather than leaving a gap in
+    /// the numbering.
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    pub dropped_questions: Vec<u32>,
     /// What to do about each question that raised something.
     pub triage: Triage,
     /// How the authored expectations did.
@@ -1478,6 +1509,13 @@ pub fn cohort(
         .filter_map(|item| questions.iter().find(|q| q.number == item.number).cloned())
         .collect();
 
+    let mut dropped_questions: Vec<u32> = set
+        .all_items()
+        .into_iter()
+        .filter(|n| set.item_dropped(*n))
+        .collect();
+    dropped_questions.sort_unstable();
+
     let default_options = course.policy.options_per_item;
     let triage = triage(&questions, threshold, default_options);
     let predictions = prediction_summary(analysis);
@@ -1490,6 +1528,7 @@ pub fn cohort(
         distribution: distribution(&percents),
         grades,
         lectures,
+        dropped_questions,
         triage,
         predictions,
         reliability: ReliabilityRow {
@@ -2193,6 +2232,7 @@ mod tests {
             strengths: Vec::new(),
             focus: Vec::new(),
             questions: Vec::new(),
+            dropped_questions: Vec::new(),
             review_lectures: Vec::new(),
             study: Vec::new(),
         })