Merge 'Prevent DROP TABLE when table is referenced by foreign keys' from Joao Faria

## Related issue
- closes #3885
## Description
Add a check to reject dropping a table when PRAGMA foreign_keys=ON and
the table is referenced by foreign keys

Reviewed-by: Preston Thorpe <preston@turso.tech>

Closes #3913

core/translate/mod.rs

@@ -231,7 +231,7 @@ pub fn translate_inner(
         ast::Stmt::DropTable {
             if_exists,
             tbl_name,
-        } => translate_drop_table(tbl_name, resolver, if_exists, program)?,
+        } => translate_drop_table(tbl_name, resolver, if_exists, program, connection)?,
         ast::Stmt::DropTrigger { .. } => bail_parse_error!("DROP TRIGGER not supported yet"),
         ast::Stmt::DropView {
             if_exists,

core/translate/schema.rs

@@ -13,7 +13,7 @@ use crate::util::PRIMARY_KEY_AUTOMATIC_INDEX_NAME_PREFIX;
 use crate::vdbe::builder::CursorType;
 use crate::vdbe::insn::{CmpInsFlags, Cookie, InsertFlags, Insn};
 use crate::Connection;
-use crate::{bail_parse_error, Result};
+use crate::{bail_constraint_error, bail_parse_error, Result};
 
 use turso_ext::VTabKind;
 
@@ -608,6 +608,7 @@ pub fn translate_drop_table(
     resolver: &Resolver,
     if_exists: bool,
     mut program: ProgramBuilder,
+    connection: &Connection,
 ) -> Result<ProgramBuilder> {
     if tbl_name
         .name
@@ -657,6 +658,15 @@ pub fn translate_drop_table(
             tbl_name.name.as_str()
         );
     }
+
+    // Check if foreign keys are enabled and if this table is referenced by foreign keys
+    if connection.foreign_keys_enabled()
+        && resolver
+            .schema
+            .any_resolved_fks_referencing(table.get_name())
+    {
+        bail_constraint_error!("FOREIGN KEY constraint failed");
+    }
     let cdc_table = prepare_cdc_if_necessary(&mut program, resolver.schema, SQLITE_TABLEID)?;
 
     let null_reg = program.alloc_register(); //  r1

testing/drop_table.test

@@ -62,3 +62,24 @@ do_execsql_test_on_specific_db {:memory:} drop-table-after-ops-1 {
     DROP TABLE t6;
     SELECT count(*) FROM sqlite_schema WHERE type='table' AND name='t6';
 } {0}
+
+# Test that DROP TABLE fails when table is referenced by foreign keys
+do_execsql_test_in_memory_any_error drop-table-fk-constraint-failed {
+    PRAGMA foreign_keys=ON;
+    CREATE TABLE parent(a INTEGER PRIMARY KEY);
+    CREATE TABLE child(a INTEGER PRIMARY KEY, b INTEGER, FOREIGN KEY(b) REFERENCES parent(a));
+    INSERT INTO parent VALUES (1);
+    INSERT INTO child VALUES (123, 1);
+    DROP TABLE parent;
+}
+
+# Test that DROP TABLE succeeds when foreign keys are disabled
+do_execsql_test_on_specific_db {:memory:} drop-table-fk-disabled-ok {
+    PRAGMA foreign_keys=OFF;
+    CREATE TABLE parent(a INTEGER PRIMARY KEY);
+    CREATE TABLE child(a INTEGER PRIMARY KEY, b INTEGER, FOREIGN KEY(b) REFERENCES parent(a));
+    INSERT INTO parent VALUES (1);
+    INSERT INTO child VALUES (123, 1);
+    DROP TABLE parent;
+    SELECT count(*) FROM sqlite_schema WHERE type='table' AND name='parent';
+} {0}