Iterate on both index constraint and usage

src/vtab/array.rs

@@ -91,8 +91,8 @@ unsafe impl<'vtab> VTab<'vtab> for ArrayTab {
 
     fn best_index(&self, info: &mut IndexInfo) -> Result<()> {
         // Index of the pointer= constraint
-        let mut ptr_idx = None;
+        let mut ptr_idx = false;
-        for (i, constraint) in info.constraints().enumerate() {
+        for (constraint, mut constraint_usage) in info.constraints_and_usages() {
             if !constraint.is_usable() {
                 continue;
             }
@@ -100,15 +100,12 @@ unsafe impl<'vtab> VTab<'vtab> for ArrayTab {
                 continue;
             }
             if let CARRAY_COLUMN_POINTER = constraint.column() {
-                ptr_idx = Some(i);
+                ptr_idx = true;
-            }
-        }
-        if let Some(ptr_idx) = ptr_idx {
-            {
-                let mut constraint_usage = info.constraint_usage(ptr_idx);
                 constraint_usage.set_argv_index(1);
                 constraint_usage.set_omit(true);
             }
+        }
+        if ptr_idx {
             info.set_estimated_cost(1f64);
             info.set_estimated_rows(100);
             info.set_idx_num(1);

src/vtab/mod.rs

@@ -309,6 +309,19 @@ impl From<u8> for IndexConstraintOp {
 pub struct IndexInfo(*mut ffi::sqlite3_index_info);
 
 impl IndexInfo {
+    /// Iterate on index constraint and its associated usage.
+    #[inline]
+    pub fn constraints_and_usages(&mut self) -> IndexConstraintAndUsageIter<'_> {
+        let constraints =
+            unsafe { slice::from_raw_parts((*self.0).aConstraint, (*self.0).nConstraint as usize) };
+        let constraint_usages = unsafe {
+            slice::from_raw_parts_mut((*self.0).aConstraintUsage, (*self.0).nConstraint as usize)
+        };
+        IndexConstraintAndUsageIter {
+            iter: constraints.iter().zip(constraint_usages.iter_mut()),
+        }
+    }
+
     /// Record WHERE clause constraints.
     #[inline]
     pub fn constraints(&self) -> IndexConstraintIter<'_> {
@@ -384,6 +397,30 @@ impl IndexInfo {
     // TODO sqlite3_vtab_collation (http://sqlite.org/c3ref/vtab_collation.html)
 }
 
+/// Iterate on index constraint and its associated usage.
+pub struct IndexConstraintAndUsageIter<'a> {
+    iter: std::iter::Zip<
+        slice::Iter<'a, ffi::sqlite3_index_constraint>,
+        slice::IterMut<'a, ffi::sqlite3_index_constraint_usage>,
+    >,
+}
+
+impl<'a> Iterator for IndexConstraintAndUsageIter<'a> {
+    type Item = (IndexConstraint<'a>, IndexConstraintUsage<'a>);
+
+    #[inline]
+    fn next(&mut self) -> Option<(IndexConstraint<'a>, IndexConstraintUsage<'a>)> {
+        self.iter
+            .next()
+            .map(|raw| (IndexConstraint(raw.0), IndexConstraintUsage(raw.1)))
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
 /// `feature = "vtab"`
 pub struct IndexConstraintIter<'a> {
     iter: slice::Iter<'a, ffi::sqlite3_index_constraint>,