From 794607033084a8cef7330e2532bb52d4b9e40751 Mon Sep 17 00:00:00 2001
From: "vitess-bot[bot]" <108069721+vitess-bot[bot]@users.noreply.github.com>
Date: Thu, 21 Sep 2023 11:16:12 +0200
Subject: [PATCH] evalengine: Mark UUID() function as non-constant (#14051)

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>
---
 go/vt/vtgate/evalengine/compiler_test.go | 62 ++++++++++++++++++++++++
 go/vt/vtgate/evalengine/fn_misc.go       |  4 ++
 2 files changed, 66 insertions(+)

diff --git a/go/vt/vtgate/evalengine/compiler_test.go b/go/vt/vtgate/evalengine/compiler_test.go
index 4e1eb479834..9cc90d5a18f 100644
--- a/go/vt/vtgate/evalengine/compiler_test.go
+++ b/go/vt/vtgate/evalengine/compiler_test.go
@@ -576,3 +576,65 @@ func TestBindVarLiteral(t *testing.T) {
 		})
 	}
 }
+
+func TestCompilerNonConstant(t *testing.T) {
+	var testCases = []struct {
+		expression string
+	}{
+		{
+			expression: "RANDOM_BYTES(4)",
+		},
+		{
+			expression: "UUID()",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.expression, func(t *testing.T) {
+			expr, err := sqlparser.ParseExpr(tc.expression)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			cfg := &evalengine.Config{
+				Collation:    collations.CollationUtf8mb4ID,
+				Optimization: evalengine.OptimizationLevelCompile,
+			}
+
+			converted, err := evalengine.Translate(expr, cfg)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			env := evalengine.EmptyExpressionEnv()
+			var prev string
+			for i := 0; i < 1000; i++ {
+				expected, err := env.Evaluate(evalengine.Deoptimize(converted))
+				if err != nil {
+					t.Fatal(err)
+				}
+				if expected.String() == prev {
+					t.Fatalf("constant evaluation from eval engine: got %s multiple times", expected.String())
+				}
+				prev = expected.String()
+			}
+
+			if cfg.CompilerErr != nil {
+				t.Fatalf("bad compilation: %v", cfg.CompilerErr)
+			}
+
+			// re-run the same evaluation multiple times to ensure results are always consistent
+			for i := 0; i < 1000; i++ {
+				res, err := env.EvaluateVM(converted.(*evalengine.CompiledExpr))
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				if res.String() == prev {
+					t.Fatalf("constant evaluation from eval engine: got %s multiple times", res.String())
+				}
+				prev = res.String()
+			}
+		})
+	}
+}
diff --git a/go/vt/vtgate/evalengine/fn_misc.go b/go/vt/vtgate/evalengine/fn_misc.go
index 96522a2314f..04770c387af 100644
--- a/go/vt/vtgate/evalengine/fn_misc.go
+++ b/go/vt/vtgate/evalengine/fn_misc.go
@@ -586,6 +586,10 @@ func (call *builtinUUID) compile(c *compiler) (ctype, error) {
 	return ctype{Type: sqltypes.VarChar, Flag: 0, Col: collationUtf8mb3}, nil
 }
 
+func (call *builtinUUID) constant() bool {
+	return false
+}
+
 func (call *builtinUUIDToBin) eval(env *ExpressionEnv) (eval, error) {
 	arg, err := call.arg1(env)
 	if arg == nil || err != nil {