Merge #49578

49578: sql: refactor casts and add volatility information r=RaduBerinde a=RaduBerinde

#### sql: move code related to casts into separate file

Release note: None

#### sql: refactor casts and add volatility information

This change refactors the lists of valid casts into a single list and associated
lookup-up map. The new list defines casts between *families* of types, which was
effectively what was happening before but in a more roundabout way.

The casts now have volatility information, which will be used by the optimizer;
the list was obtained by auditing the usage of `ctx` in `PerformCast`.

Informs #48717.

Release note: None

Co-authored-by: Radu Berinde <[email protected]>

pkg/sql/sem/tree/casts_test.go

@@ -0,0 +1,121 @@
+// Copyright 2020 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+package tree
+
+import (
+	"encoding/csv"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/sql/oidext"
+	"github.com/cockroachdb/cockroach/pkg/sql/types"
+	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+	"github.com/lib/pq/oid"
+	"github.com/stretchr/testify/require"
+)
+
+// TestCastsVolatilityMatchesPostgres checks that our defined casts match
+// Postgres' casts for Volatility.
+//
+// Dump command below:
+// COPY (
+//   SELECT c.castsource, c.casttarget, p.provolatile FROM pg_cast c JOIN pg_proc p ON (c.castfunc = p.oid)
+// ) TO STDOUT WITH CSV DELIMITER '|' HEADER;
+func TestCastsVolatilityMatchesPostgres(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	csvPath := filepath.Join("testdata", "pg_cast_provolatile_dump.csv")
+	f, err := os.Open(csvPath)
+	require.NoError(t, err)
+
+	defer f.Close()
+
+	reader := csv.NewReader(f)
+	reader.Comma = '|'
+
+	// Read header row
+	_, err = reader.Read()
+	require.NoError(t, err)
+
+	type pgCast struct {
+		from, to    oid.Oid
+		provolatile byte
+	}
+	var pgCasts []pgCast
+
+	for {
+		line, err := reader.Read()
+		if err == io.EOF {
+			break
+		}
+		require.Len(t, line, 3)
+		require.NoError(t, err)
+
+		fromOid, err := strconv.Atoi(line[0])
+		require.NoError(t, err)
+
+		toOid, err := strconv.Atoi(line[1])
+		require.NoError(t, err)
+
+		provolatile := line[2]
+		require.Len(t, provolatile, 1)
+		pgCasts = append(pgCasts, pgCast{
+			from:        oid.Oid(fromOid),
+			to:          oid.Oid(toOid),
+			provolatile: provolatile[0],
+		})
+	}
+
+	oidToFamily := func(o oid.Oid) (_ types.Family, ok bool) {
+		t, ok := types.OidToType[o]
+		if !ok {
+			return 0, false
+		}
+		return t.Family(), true
+	}
+
+	oidStr := func(o oid.Oid) string {
+		res, ok := oidext.TypeName(o)
+		if !ok {
+			res = fmt.Sprintf("%d", o)
+		}
+		return res
+	}
+
+	for _, c := range validCasts {
+		if c.ignoreVolatilityCheck {
+			continue
+		}
+
+		// Look through all pg casts and find any where the Oids map to these
+		// families.
+		found := false
+		for i := range pgCasts {
+			fromFamily, fromOk := oidToFamily(pgCasts[i].from)
+			toFamily, toOk := oidToFamily(pgCasts[i].to)
+			if fromOk && toOk && fromFamily == c.from && toFamily == c.to {
+				found = true
+				if c.volatility != Volatility(pgCasts[i].provolatile) {
+					t.Errorf("cast %s::%s has volatility '%c'; corresponding pg cast %s::%s has volatility '%c'",
+						c.from.Name(), c.to.Name(), c.volatility,
+						oidStr(pgCasts[i].from), oidStr(pgCasts[i].to), pgCasts[i].provolatile,
+					)
+				}
+			}
+		}
+		if !found && testing.Verbose() {
+			t.Logf("cast %s::%s has no corresponding pg cast", c.from.Name(), c.to.Name())
+		}
+	}
+}