Merge 'Adjust vtab schema creation to display the underlying columns' from Preston Thorpe

### The problem:
Sqlite displays the column names of the underlying vtab module when
displaying the `.schema`
![image](https://github.com/user-
attachments/assets/ca6aa1c9-0af7-4f34-a5c4-c8336fa23858)
Previously limbo omitted this, which makes it difficult for the user to
see what/how many columns the module's table has.
This matches sqlite's behavior by fetching the module's schema when the
schema entry is being inserted in translation.
![image](https://github.com/user-
attachments/assets/a56b8239-0f65-420b-a0b6-536ede117fba)

Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>

Closes #1168

core/translate/mod.rs

@@ -97,7 +97,7 @@ pub fn translate(
         ast::Stmt::CreateTrigger { .. } => bail_parse_error!("CREATE TRIGGER not supported yet"),
         ast::Stmt::CreateView { .. } => bail_parse_error!("CREATE VIEW not supported yet"),
         ast::Stmt::CreateVirtualTable(vtab) => {
-            translate_create_virtual_table(*vtab, schema, query_mode)?
+            translate_create_virtual_table(*vtab, schema, query_mode, &syms)?
         }
         ast::Stmt::Delete(delete) => {
             let Delete {

core/translate/schema.rs

@@ -1,6 +1,8 @@
 use std::fmt::Display;
+use std::rc::Rc;
 
 use crate::ast;
+use crate::ext::VTabImpl;
 use crate::schema::Schema;
 use crate::schema::Table;
 use crate::storage::pager::CreateBTreeFlags;
@@ -11,8 +13,10 @@ use crate::util::PRIMARY_KEY_AUTOMATIC_INDEX_NAME_PREFIX;
 use crate::vdbe::builder::CursorType;
 use crate::vdbe::insn::{CmpInsFlags, Insn};
 use crate::LimboError;
+use crate::SymbolTable;
 use crate::{bail_parse_error, Result};
 
+use limbo_ext::VTabKind;
 use limbo_sqlite3_parser::ast::{fmt::ToTokens, CreateVirtualTable};
 
 pub fn translate_create_table(
@@ -396,7 +400,7 @@ fn create_table_body_to_str(tbl_name: &ast::QualifiedName, body: &ast::CreateTab
     sql
 }
 
-fn create_vtable_body_to_str(vtab: &CreateVirtualTable) -> String {
+fn create_vtable_body_to_str(vtab: &CreateVirtualTable, module: Rc<VTabImpl>) -> String {
     let args = if let Some(args) = &vtab.args {
         args.iter()
             .map(|arg| arg.to_string())
@@ -410,8 +414,25 @@ fn create_vtable_body_to_str(vtab: &CreateVirtualTable) -> String {
     } else {
         ""
     };
+    let ext_args = vtab
+        .args
+        .as_ref()
+        .unwrap_or(&vec![])
+        .iter()
+        .map(|a| limbo_ext::Value::from_text(a.to_string()))
+        .collect::<Vec<_>>();
+    let schema = module
+        .implementation
+        .init_schema(ext_args)
+        .unwrap_or_default();
+    let vtab_args = if let Some(first_paren) = schema.find('(') {
+        let closing_paren = schema.rfind(')').unwrap_or_default();
+        &schema[first_paren..=closing_paren]
+    } else {
+        "()"
+    };
     format!(
-        "CREATE VIRTUAL TABLE {} {} USING {}{}",
+        "CREATE VIRTUAL TABLE {} {} USING {}{}\n /*{}{}*/",
         vtab.tbl_name.name.0,
         if_not_exists,
         vtab.module_name.0,
@@ -419,7 +440,9 @@ fn create_vtable_body_to_str(vtab: &CreateVirtualTable) -> String {
             String::new()
         } else {
             format!("({})", args)
-        }
+        },
+        vtab.tbl_name.name.0,
+        vtab_args
     )
 }
 
@@ -427,6 +450,7 @@ pub fn translate_create_virtual_table(
     vtab: CreateVirtualTable,
     schema: &Schema,
     query_mode: QueryMode,
+    syms: &SymbolTable,
 ) -> Result<ProgramBuilder> {
     let ast::CreateVirtualTable {
         if_not_exists,
@@ -438,7 +462,12 @@ pub fn translate_create_virtual_table(
     let table_name = tbl_name.name.0.clone();
     let module_name_str = module_name.0.clone();
     let args_vec = args.clone().unwrap_or_default();
-
+    let Some(vtab_module) = syms.vtab_modules.get(&module_name_str) else {
+        bail_parse_error!("no such module: {}", module_name_str);
+    };
+    if !vtab_module.module_kind.eq(&VTabKind::VirtualTable) {
+        bail_parse_error!("module {} is not a virtual table", module_name_str);
+    };
     if schema.get_table(&table_name).is_some() && *if_not_exists {
         let mut program = ProgramBuilder::new(ProgramBuilderOpts {
             query_mode,
@@ -464,7 +493,6 @@ pub fn translate_create_virtual_table(
     let start_offset = program.offset();
     let module_name_reg = program.emit_string8_new_reg(module_name_str.clone());
     let table_name_reg = program.emit_string8_new_reg(table_name.clone());
-
     let args_reg = if !args_vec.is_empty() {
         let args_start = program.alloc_register();
 
@@ -490,7 +518,6 @@ pub fn translate_create_virtual_table(
         table_name: table_name_reg,
         args_reg,
     });
-
     let table = schema.get_btree_table(SQLITE_TABLEID).unwrap();
     let sqlite_schema_cursor_id = program.alloc_cursor_id(
         Some(SQLITE_TABLEID.to_owned()),
@@ -501,7 +528,7 @@ pub fn translate_create_virtual_table(
         root_page: 1usize.into(),
     });
 
-    let sql = create_vtable_body_to_str(&vtab);
+    let sql = create_vtable_body_to_str(&vtab, vtab_module.clone());
     emit_schema_entry(
         &mut program,
         sqlite_schema_cursor_id,

testing/cli_tests/extensions.py

@@ -345,7 +345,7 @@ def test_kv():
     limbo.execute_dot("INSERT INTO other values (23,32,23);")
     limbo.run_test_fn(
         "create virtual table t using kv_store;",
-        lambda res: "Module kv_store not found" in res,
+        lambda res: "Parse error: no such module: kv_store" in res,
     )
     limbo.execute_dot(f".load {ext_path}")
     limbo.execute_dot(