Dynamic cursor ID allocation

With sorter, for example, we need more cursors per program.

core/translate.rs

@@ -21,7 +21,7 @@ fn translate_select(schema: &Schema, select: Select) -> Result<Program> {
             from: Some(from),
             ..
         } => {
-            let cursor_id = 0;
+            let cursor_id = program.alloc_cursor_id();
             let table_name = match from.select {
                 Some(select_table) => match *select_table {
                     sqlite3_parser::ast::SelectTable::Table(name, ..) => name.name,
@@ -47,7 +47,7 @@ fn translate_select(schema: &Schema, select: Select) -> Result<Program> {
                 None
             };
             program.emit_insn(Insn::OpenReadAsync {
-                cursor_id: 0,
+                cursor_id,
                 root_page,
             });
             program.emit_insn(Insn::OpenReadAwait);

core/vdbe.rs

@@ -97,6 +97,7 @@ pub enum Insn {
 
 pub struct ProgramBuilder {
     next_free_register: usize,
+    next_free_cursor_id: usize,
     insns: Vec<Insn>,
 }
 
@@ -104,6 +105,7 @@ impl ProgramBuilder {
     pub fn new() -> Self {
         Self {
             next_free_register: 0,
+            next_free_cursor_id: 0,
             insns: Vec::new(),
         }
     }
@@ -118,6 +120,12 @@ impl ProgramBuilder {
         self.next_free_register
     }
 
+    pub fn alloc_cursor_id(&mut self) -> usize {
+        let cursor = self.next_free_cursor_id;
+        self.next_free_cursor_id += 1;
+        cursor
+    }
+
     pub fn emit_placeholder(&mut self) -> usize {
         let offset = self.insns.len();
         self.insns.push(Insn::Halt);