Cherry-pick 5fd70c4 with conflicts

go/vt/vtgate/engine/projection.go

@@ -74,7 +74,11 @@ func (p *Projection) TryExecute(ctx context.Context, vcursor VCursor, bindVars m
 		resultRows = append(resultRows, resultRow)
 	}
 	if wantfields {
+<<<<<<< HEAD
 		result.Fields, err = p.evalFields(env, result.Fields, vcursor)
+=======
+		result.Fields, err = p.evalFields(env, result.Fields, vcursor.ConnCollation())
+>>>>>>> 5fd70c4323 (projection: Return correct collation information (#15801))
 		if err != nil {
 			return nil, err
 		}
@@ -95,7 +99,11 @@ func (p *Projection) TryStreamExecute(ctx context.Context, vcursor VCursor, bind
 		defer mu.Unlock()
 		if wantfields {
 			once.Do(func() {
+<<<<<<< HEAD
 				fields, err = p.evalFields(env, qr.Fields, vcursor)
+=======
+				fields, err = p.evalFields(env, qr.Fields, vcursor.ConnCollation())
+>>>>>>> 5fd70c4323 (projection: Return correct collation information (#15801))
 				if err != nil {
 					return
 				}
@@ -134,14 +142,26 @@ func (p *Projection) GetFields(ctx context.Context, vcursor VCursor, bindVars ma
 		return nil, err
 	}
 	env := evalengine.NewExpressionEnv(ctx, bindVars, vcursor)
+<<<<<<< HEAD
 	qr.Fields, err = p.evalFields(env, qr.Fields, vcursor)
+=======
+	qr.Fields, err = p.evalFields(env, qr.Fields, vcursor.ConnCollation())
+>>>>>>> 5fd70c4323 (projection: Return correct collation information (#15801))
 	if err != nil {
 		return nil, err
 	}
 	return qr, nil
 }
 
+<<<<<<< HEAD
 func (p *Projection) evalFields(env *evalengine.ExpressionEnv, infields []*querypb.Field, vcursor VCursor) ([]*querypb.Field, error) {
+=======
+func (p *Projection) evalFields(env *evalengine.ExpressionEnv, infields []*querypb.Field, coll collations.ID) ([]*querypb.Field, error) {
+	// TODO: once the evalengine becomes smart enough, we should be able to remove the
+	// dependency on these fields altogether
+	env.Fields = infields
+
+>>>>>>> 5fd70c4323 (projection: Return correct collation information (#15801))
 	var fields []*querypb.Field
 	for i, col := range p.Cols {
 		q, f, err := env.TypeOf(p.Exprs[i], infields)
@@ -157,11 +177,25 @@ func (p *Projection) evalFields(env *evalengine.ExpressionEnv, infields []*query
 		if !sqltypes.IsNull(q) && !f.Nullable() {
 			fl |= uint32(querypb.MySqlFlag_NOT_NULL_FLAG)
 		}
+		typCol := typ.Collation()
+		if sqltypes.IsTextOrBinary(typ.Type()) && typCol != collations.CollationBinaryID {
+			typCol = coll
+		}
+
 		fields = append(fields, &querypb.Field{
+<<<<<<< HEAD
 			Name:    col,
 			Type:    q,
 			Charset: uint32(cs),
 			Flags:   fl,
+=======
+			Name:         col,
+			Type:         typ.Type(),
+			Charset:      uint32(typCol),
+			ColumnLength: uint32(typ.Size()),
+			Decimals:     uint32(typ.Scale()),
+			Flags:        fl,
+>>>>>>> 5fd70c4323 (projection: Return correct collation information (#15801))
 		})
 	}
 	return fields, nil

go/vt/vtgate/engine/projection_test.go

@@ -212,3 +212,41 @@ func TestFields(t *testing.T) {
 		})
 	}
 }
+
+func TestFieldConversion(t *testing.T) {
+	var testCases = []struct {
+		name      string
+		expr      string
+		typ       querypb.Type
+		collation collations.ID
+	}{
+		{
+			name:      `convert different charset`,
+			expr:      `_latin1 0xFF`,
+			typ:       sqltypes.VarChar,
+			collation: collations.MySQL8().DefaultConnectionCharset(),
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			arg, err := sqlparser.NewTestParser().ParseExpr(testCase.expr)
+			require.NoError(t, err)
+			bindExpr, err := evalengine.Translate(arg, &evalengine.Config{
+				Environment: vtenv.NewTestEnv(),
+				Collation:   collations.MySQL8().DefaultConnectionCharset(),
+			})
+			require.NoError(t, err)
+			proj := &Projection{
+				Cols:       []string{"col"},
+				Exprs:      []evalengine.Expr{bindExpr},
+				Input:      &SingleRow{},
+				noTxNeeded: noTxNeeded{},
+			}
+			qr, err := proj.TryExecute(context.Background(), &noopVCursor{}, nil, true)
+			require.NoError(t, err)
+			assert.Equal(t, testCase.typ, qr.Fields[0].Type)
+			assert.Equal(t, testCase.collation, collations.ID(qr.Fields[0].Charset))
+		})
+	}
+}