Add read implementation of user_version pragma with ReadCookie opcode

COMPAT.md

@@ -160,7 +160,7 @@ The current status of Limbo is:
 | PRAGMA temp_store_directory      | Not Needed | deprecated in SQLite                         |
 | PRAGMA threads                   | No         |                                              |
 | PRAGMA trusted_schema            | No         |                                              |
-| PRAGMA user_version              | No         |                                              |
+| PRAGMA user_version              | Partial    | Only read implemented                        |
 | PRAGMA vdbe_addoptrace           | No         |                                              |
 | PRAGMA vdbe_debug                | No         |                                              |
 | PRAGMA vdbe_listing              | No         |                                              |
@@ -514,7 +514,7 @@ Modifiers:
 | PrevAsync      | Yes    |         |
 | PrevAwait      | Yes    |         |
 | Program        | No     |         |
-| ReadCookie     | No     |         |
+| ReadCookie     | Partial| no temp databases, only user_version supported |
 | Real           | Yes    |         |
 | RealAffinity   | Yes    |         |
 | Remainder      | Yes    |         |

core/storage/sqlite3_ondisk.rs

@@ -128,7 +128,7 @@ pub struct DatabaseHeader {
     text_encoding: u32,
 
     /// The "user version" as read and set by the user_version pragma.
-    user_version: u32,
+    pub user_version: u32,
 
     /// True (non-zero) for incremental-vacuum mode. False (zero) otherwise.
     incremental_vacuum_enabled: u32,
@@ -232,7 +232,7 @@ impl Default for DatabaseHeader {
             default_page_cache_size: 500, // pages
             vacuum_mode_largest_root_page: 0,
             text_encoding: 1, // utf-8
-            user_version: 1,
+            user_version: 0,
             incremental_vacuum_enabled: 0,
             application_id: 0,
             reserved_for_expansion: [0; 20],

core/translate/pragma.rs

@@ -11,7 +11,7 @@ use crate::storage::sqlite3_ondisk::{DatabaseHeader, MIN_PAGE_CACHE_SIZE};
 use crate::storage::wal::CheckpointMode;
 use crate::util::normalize_ident;
 use crate::vdbe::builder::{ProgramBuilder, ProgramBuilderOpts, QueryMode};
-use crate::vdbe::insn::Insn;
+use crate::vdbe::insn::{Cookie, Insn};
 use crate::vdbe::BranchOffset;
 use crate::{bail_parse_error, Pager};
 use std::str::FromStr;
@@ -148,6 +148,10 @@ fn update_pragma(
             query_pragma(PragmaName::PageCount, schema, None, header, program)?;
             Ok(())
         }
+        PragmaName::UserVersion => {
+            // TODO: Implement updating user_version
+            todo!("updating user_version not yet implemented")
+        }
         PragmaName::TableInfo => {
             // because we need control over the write parameter for the transaction,
             // this should be unreachable. We have to force-call query_pragma before
@@ -241,6 +245,15 @@ fn query_pragma(
                 }
             }
         }
+        PragmaName::UserVersion => {
+            program.emit_transaction(false);
+            program.emit_insn(Insn::ReadCookie {
+                db: 0,
+                dest: register,
+                cookie: Cookie::UserVersion,
+            });
+            program.emit_result_row(register, 1);
+        }
     }
 
     Ok(())

core/vdbe/explain.rs

@@ -1232,6 +1232,15 @@ pub fn insn_to_str(
                 0,
                 "".to_string(),
             ),
+            Insn::ReadCookie { db, dest, cookie } => (
+                "ReadCookie",
+                *db as i32,
+                *dest as i32,
+                *cookie as i32,
+                OwnedValue::build_text(Rc::new("".to_string())),
+                0,
+                "".to_string(),
+            ),
         };
     format!(
         "{:<4}  {:<17}  {:<4}  {:<4}  {:<4}  {:<13}  {:<2}  {}",

core/vdbe/insn.rs

@@ -639,6 +639,29 @@ pub enum Insn {
         db: usize,
         dest: usize,
     },
+    /// Read cookie number P3 from database P1 and write it into register P2
+    ReadCookie {
+        db: usize,
+        dest: usize,
+        cookie: Cookie,
+    },
+}
+
+// TODO: Add remaining cookies.
+#[derive(Description, Debug, Clone, Copy)]
+pub enum Cookie {
+    /// The schema cookie.
+    SchemaVersion = 1,
+    /// The schema format number. Supported schema formats are 1, 2, 3, and 4.
+    DatabaseFormat = 2,
+    /// Default page cache size.
+    DefaultPageCacheSize = 3,
+    /// The page number of the largest root b-tree page when in auto-vacuum or incremental-vacuum modes, or zero otherwise.
+    LargestRootPageNumber = 4,
+    /// The database text encoding. A value of 1 means UTF-8. A value of 2 means UTF-16le. A value of 3 means UTF-16be.
+    DatabaseTextEncoding = 5,
+    /// The "user version" as read and set by the user_version pragma.
+    UserVersion = 6,
 }
 
 fn cast_text_to_numerical(value: &str) -> OwnedValue {

core/vdbe/mod.rs

@@ -55,7 +55,7 @@ use crate::{resolve_ext_path, Connection, Result, TransactionState, DATABASE_VER
 use insn::{
     exec_add, exec_and, exec_bit_and, exec_bit_not, exec_bit_or, exec_boolean_not, exec_concat,
     exec_divide, exec_multiply, exec_or, exec_remainder, exec_shift_left, exec_shift_right,
-    exec_subtract,
+    exec_subtract, Cookie,
 };
 use likeop::{construct_like_escape_arg, exec_glob, exec_like_with_escape};
 use rand::distributions::{Distribution, Uniform};
@@ -2662,6 +2662,18 @@ impl Program {
                     parse_schema_rows(Some(stmt), &mut schema, conn.pager.io.clone())?;
                     state.pc += 1;
                 }
+                Insn::ReadCookie { db, dest, cookie } => {
+                    if *db > 0 {
+                        // TODO: implement temp databases
+                        todo!("temp databases not implemented yet");
+                    }
+                    let cookie_value = match cookie {
+                        Cookie::UserVersion => pager.db_header.borrow().user_version.into(),
+                        cookie => todo!("{cookie:?} is not yet implement for ReadCookie"),
+                    };
+                    state.registers[*dest] = OwnedValue::Integer(cookie_value);
+                    state.pc += 1;
+                }
                 Insn::ShiftRight { lhs, rhs, dest } => {
                     state.registers[*dest] =
                         exec_shift_right(&state.registers[*lhs], &state.registers[*rhs]);

testing/pragma.test

@@ -41,3 +41,11 @@ do_execsql_test_on_specific_db ":memory:" pragma-page-count-table {
   CREATE TABLE foo(bar);
   PRAGMA page_count
 } {2}
+
+do_execsql_test_on_specific_db "testing/testing_user_version_10.db" pragma-user-version-user-set {
+  PRAGMA user_version
+} {10}
+
+do_execsql_test_on_specific_db ":memory:" pragma-user-version-default {
+  PRAGMA user_version
+} {0}

vendored/sqlite3-parser/src/parser/ast/mod.rs

@@ -1598,6 +1598,8 @@ pub enum PragmaName {
     PageCount,
     /// returns information about the columns of a table
     TableInfo,
+    /// Returns the user version of the database file.
+    UserVersion,
     /// trigger a checkpoint to run on database(s) if WAL is enabled
     WalCheckpoint,
 }