plpgsql: add builtin function for closing cursors

This patch adds the `crdb_internal.plpgsql_close` builtin, which closes
the cursor with the given name. It returns a `34000` error if there is
no cursor with the given name. A following commit will use this to
implement the PLpgSQL CLOSE statement.

Informs cockroachdb#109709

Release note: None

pkg/sql/faketreeeval/evalctx.go

@@ -332,6 +332,11 @@ func (*DummyEvalPlanner) Optimizer() interface{} {
 	return nil
 }
 
+// PLpgSQLCloseCursor is part of the eval.Planner interface.
+func (*DummyEvalPlanner) PLpgSQLCloseCursor(_ tree.Name) error {
+	return nil
+}
+
 var _ eval.Planner = &DummyEvalPlanner{}
 
 var errEvalPlanner = pgerror.New(pgcode.ScalarOperationCannotRunWithoutFullSessionContext,

pkg/sql/logictest/testdata/logic_test/plpgsql_builtins

@@ -0,0 +1,22 @@
+# Testing crdb_internal.plpgsql_close.
+statement ok
+BEGIN;
+DECLARE foo CURSOR FOR SELECT generate_series(1, 5);
+
+query T
+SELECT name FROM pg_cursors;
+----
+foo
+
+statement ok
+SELECT crdb_internal.plpgsql_close('foo');
+
+query T
+SELECT name FROM pg_cursors;
+----
+
+statement ok
+ABORT;
+
+statement error pgcode 34000 pq: cursor \"foo\" does not exist
+SELECT crdb_internal.plpgsql_close('foo');

pkg/sql/sem/builtins/builtins.go

@@ -8431,6 +8431,24 @@ specified store on the node it's run from. One of 'mvccGC', 'merge', 'split',
 			Volatility: volatility.Immutable,
 		},
 	),
+	"crdb_internal.plpgsql_close": makeBuiltin(tree.FunctionProperties{
+		Category:     builtinconstants.CategoryString,
+		Undocumented: true,
+	},
+		tree.Overload{
+			Types:      tree.ParamTypes{{Name: "name", Typ: types.String}},
+			ReturnType: tree.FixedReturnType(types.Int),
+			Fn: func(ctx context.Context, evalCtx *eval.Context, args tree.Datums) (tree.Datum, error) {
+				if args[0] == tree.DNull {
+					return nil, errors.AssertionFailedf("expected non-null argument for plpgsql_close")
+				}
+				return tree.DNull, evalCtx.Planner.PLpgSQLCloseCursor(tree.Name(tree.MustBeDString(args[0])))
+			},
+			Info:              "This function is used internally to implement the PLpgSQL CLOSE statement.",
+			Volatility:        volatility.Volatile,
+			CalledOnNullInput: true,
+		},
+	),
 }
 
 var lengthImpls = func(incBitOverload bool) builtinDefinition {

pkg/sql/sem/builtins/fixed_oids.go

@@ -2463,6 +2463,7 @@ var builtinOidsArray = []string{
 	2492: `make_timestamptz(year: int, month: int, day: int, hour: int, min: int, sec: float, timezone: string) -> timestamptz`,
 	2493: `date_trunc(element: string, input: timestamptz, timezone: string) -> timestamptz`,
 	2494: `make_date(year: int, month: int, day: int) -> date`,
+	2495: `crdb_internal.plpgsql_close(name: string) -> int`,
 }
 
 var builtinOidsBySignature map[string]oid.Oid

pkg/sql/sem/eval/deps.go

@@ -404,6 +404,11 @@ type Planner interface {
 
 	// Optimizer returns the optimizer associated with this Planner, if any.
 	Optimizer() interface{}
+
+  // PLpgSQLCloseCursor closes the cursor with the given name, returning an
+  // error if the cursor doesn't exist. It is used to implement the PLpgSQL
+  // CLOSE statement.
+  PLpgSQLCloseCursor(cursorName tree.Name) error
 }
 
 // InternalRows is an iterator interface that's exposed by the internal

pkg/sql/sem/tree/eval.go

@@ -2052,7 +2052,8 @@ func (e *MultipleResultsError) Error() string {
 func (expr *FuncExpr) MaybeWrapError(err error) error {
 	// If we are facing an explicit error, propagate it unchanged.
 	fName := expr.Func.String()
-	if fName == `crdb_internal.force_error` || fName == `crdb_internal.plpgsql_raise` {
+	if fName == `crdb_internal.force_error` || fName == `crdb_internal.plpgsql_raise` ||
+		fName == `crdb_internal.plpgsql_close` {
 		return err
 	}
 	// Otherwise, wrap it with context.

pkg/sql/sql_cursor.go

@@ -267,6 +267,11 @@ func (p *planner) CloseCursor(ctx context.Context, n *tree.CloseCursor) (planNod
 	}, nil
 }
 
+// PLpgSQLCloseCursor implements the eval.Planner interface.
+func (p *planner) PLpgSQLCloseCursor(cursorName tree.Name) error {
+	return p.sqlCursors.closeCursor(cursorName)
+}
+
 type sqlCursor struct {
 	isql.Rows
 	// txn is the transaction object that the internal executor for this cursor