Merge 'emit proper column information for explain prepared statements' from Nikita Sivukhin

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

Closes #3612

bindings/javascript/packages/wasm/promise.test.ts

@@ -1,6 +1,97 @@
 import { expect, test } from 'vitest'
 import { connect, Database } from './promise-default.js'
 
+test('explain', async () => {
+    const db = await connect(":memory:");
+    const stmt = db.prepare("EXPLAIN SELECT 1");
+    expect(stmt.columns()).toEqual([
+        {
+            "name": "addr",
+            "type": "INTEGER",
+        },
+        {
+            "name": "opcode",
+            "type": "TEXT",
+        },
+        {
+            "name": "p1",
+            "type": "INTEGER",
+        },
+        {
+            "name": "p2",
+            "type": "INTEGER",
+        },
+        {
+            "name": "p3",
+            "type": "INTEGER",
+        },
+        {
+            "name": "p4",
+            "type": "INTEGER",
+        },
+        {
+            "name": "p5",
+            "type": "INTEGER",
+        },
+        {
+            "name": "comment",
+            "type": "TEXT",
+        },
+    ].map(x => ({ ...x, column: null, database: null, table: null })));
+    expect(await stmt.all()).toEqual([
+        {
+            "addr": 0,
+            "comment": "Start at 3",
+            "opcode": "Init",
+            "p1": 0,
+            "p2": 3,
+            "p3": 0,
+            "p4": "",
+            "p5": 0,
+        },
+        {
+            "addr": 1,
+            "comment": "output=r[1]",
+            "opcode": "ResultRow",
+            "p1": 1,
+            "p2": 1,
+            "p3": 0,
+            "p4": "",
+            "p5": 0,
+        },
+        {
+            "addr": 2,
+            "comment": "",
+            "opcode": "Halt",
+            "p1": 0,
+            "p2": 0,
+            "p3": 0,
+            "p4": "",
+            "p5": 0,
+        },
+        {
+            "addr": 3,
+            "comment": "r[1]=1",
+            "opcode": "Integer",
+            "p1": 1,
+            "p2": 1,
+            "p3": 0,
+            "p4": "",
+            "p5": 0,
+        },
+        {
+            "addr": 4,
+            "comment": "",
+            "opcode": "Goto",
+            "p1": 0,
+            "p2": 1,
+            "p3": 0,
+            "p4": "",
+            "p5": 0,
+        },
+    ]);
+})
+
 test('in-memory db', async () => {
     const db = await connect(":memory:");
     await db.exec("CREATE TABLE t(x)");
@@ -10,6 +101,7 @@ test('in-memory db', async () => {
     expect(rows).toEqual([{ x: 1 }, { x: 3 }]);
 })
 
+
 test('implicit connect', async () => {
     const db = new Database(':memory:');
     const defer = db.prepare("SELECT * FROM t");

core/lib.rs

@@ -46,6 +46,7 @@ use crate::translate::pragma::TURSO_CDC_DEFAULT_TABLE_NAME;
 use crate::types::{WalFrameInfo, WalState};
 #[cfg(feature = "fs")]
 use crate::util::{OpenMode, OpenOptions};
+use crate::vdbe::explain::{EXPLAIN_COLUMNS_TYPE, EXPLAIN_QUERY_PLAN_COLUMNS_TYPE};
 use crate::vdbe::metrics::ConnectionMetrics;
 use crate::vtab::VirtualTable;
 use crate::{incremental::view::AllViewsTxState, translate::emitter::TransactionMode};
@@ -2667,6 +2668,17 @@ impl Statement {
     }
 
     pub fn get_column_name(&self, idx: usize) -> Cow<'_, str> {
+        if self.query_mode == QueryMode::Explain {
+            return Cow::Owned(EXPLAIN_COLUMNS.get(idx).expect("No column").to_string());
+        }
+        if self.query_mode == QueryMode::ExplainQueryPlan {
+            return Cow::Owned(
+                EXPLAIN_QUERY_PLAN_COLUMNS
+                    .get(idx)
+                    .expect("No column")
+                    .to_string(),
+            );
+        }
         match self.query_mode {
             QueryMode::Normal => {
                 let column = &self.program.result_columns.get(idx).expect("No column");
@@ -2685,6 +2697,9 @@ impl Statement {
     }
 
     pub fn get_column_table_name(&self, idx: usize) -> Option<Cow<'_, str>> {
+        if self.query_mode == QueryMode::Explain || self.query_mode == QueryMode::ExplainQueryPlan {
+            return None;
+        }
         let column = &self.program.result_columns.get(idx).expect("No column");
         match &column.expr {
             turso_parser::ast::Expr::Column { table, .. } => self
@@ -2697,6 +2712,22 @@ impl Statement {
     }
 
     pub fn get_column_type(&self, idx: usize) -> Option<String> {
+        if self.query_mode == QueryMode::Explain {
+            return Some(
+                EXPLAIN_COLUMNS_TYPE
+                    .get(idx)
+                    .expect("No column")
+                    .to_string(),
+            );
+        }
+        if self.query_mode == QueryMode::ExplainQueryPlan {
+            return Some(
+                EXPLAIN_QUERY_PLAN_COLUMNS_TYPE
+                    .get(idx)
+                    .expect("No column")
+                    .to_string(),
+            );
+        }
         let column = &self.program.result_columns.get(idx).expect("No column");
         match &column.expr {
             turso_parser::ast::Expr::Column {

core/vdbe/explain.rs

@@ -6,7 +6,11 @@ use super::{Insn, InsnReference, Program, Value};
 use crate::function::{Func, ScalarFunc};
 
 pub const EXPLAIN_COLUMNS: [&str; 8] = ["addr", "opcode", "p1", "p2", "p3", "p4", "p5", "comment"];
+pub const EXPLAIN_COLUMNS_TYPE: [&str; 8] = [
+    "INTEGER", "TEXT", "INTEGER", "INTEGER", "INTEGER", "INTEGER", "INTEGER", "TEXT",
+];
 pub const EXPLAIN_QUERY_PLAN_COLUMNS: [&str; 4] = ["id", "parent", "notused", "detail"];
+pub const EXPLAIN_QUERY_PLAN_COLUMNS_TYPE: [&str; 4] = ["INTEGER", "INTEGER", "INTEGER", "TEXT"];
 
 pub fn insn_to_row(
     program: &Program,