sql: support default equivalent collations for index expressions

Previously, index expressions would work with COLLATE C because we would
always fall back to the legacy schema changer. When we moved to the
declarative schema changer, this regressed because the declarative
schema changer makes a copy of the AST by serializing and reparsing the
statement. Unfortunately, the formatting for the collation expression
did not correctly format out default equivalent collations. This patch
updates the formatter for collation expressions to special-case default
equivalent collations like POSIX, C, and DEFAULT.

Fixes: #145246

Release note: None

Author: fqazi

pkg/sql/lex/BUILD.bazel

@@ -12,6 +12,7 @@ go_library(
     deps = [
         "//pkg/sql/pgwire/pgcode",
         "//pkg/sql/pgwire/pgerror",
+        "//pkg/util/collatedstring",
         "@com_github_cockroachdb_errors//:errors",
         "@org_golang_x_text//language",
     ],

pkg/sql/lex/encode.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
+	"github.com/cockroachdb/cockroach/pkg/util/collatedstring"
 	"github.com/cockroachdb/errors"
 	"golang.org/x/text/language"
 )
@@ -42,8 +43,12 @@ func NormalizeLocaleName(s string) string {
 // need to be quoted, and they are considered equivalent to dash characters by
 // the CLDR standard: http://cldr.unicode.org/.
 func EncodeLocaleName(buf *bytes.Buffer, s string) {
-	// If possible, try to normalize the case of the locale name.
-	if normalized, err := language.Parse(s); err == nil {
+	// If possible, try to normalize the case of the locale name (only for non-default
+	// locales). Default locales will always be quoted so they can be parsed correctly.
+	isDefaultLocale := collatedstring.IsDefaultEquivalentCollation(s)
+	if isDefaultLocale {
+		s = fmt.Sprintf("%q", s)
+	} else if normalized, err := language.Parse(s); err == nil {
 		s = normalized.String()
 	}
 	for i, n := 0, len(s); i < n; i++ {

pkg/sql/logictest/testdata/logic_test/create_index

@@ -603,3 +603,33 @@ statement error pgcode 22023 pq: parameter "fillfactor" specified more than once
 CREATE INVERTED INDEX IF NOT EXISTS idx_b ON create_inverted_index_duplicate_storage_params_a (b) WITH (fillfactor=10, fillfactor=20);
 
 subtest end
+
+
+subtest create_index_expression_with_default_collation
+
+statement ok
+CREATE TABLE tbl_with_collate (c1 int);
+
+statement ok
+CREATE UNIQUE INDEX tbl_with_collate_expr ON tbl_with_collate ((c1::text COLLATE "C"));
+
+statement ok
+CREATE UNIQUE INDEX tbl_with_collate_expr2 ON tbl_with_collate ((c1::text COLLATE "POSIX"));
+
+statement ok
+CREATE UNIQUE INDEX tbl_with_collate_expr3 ON tbl_with_collate ((c1::text COLLATE "en-us"));
+
+
+query TT
+SHOW CREATE TABLE tbl_with_collate
+----
+tbl_with_collate  CREATE TABLE public.tbl_with_collate (
+                    c1 INT8 NULL,
+                    rowid INT8 NOT VISIBLE NOT NULL DEFAULT unique_rowid(),
+                    CONSTRAINT tbl_with_collate_pkey PRIMARY KEY (rowid ASC),
+                    UNIQUE INDEX tbl_with_collate_expr ((c1::STRING) ASC),
+                    UNIQUE INDEX tbl_with_collate_expr2 ((c1::STRING) ASC),
+                    UNIQUE INDEX tbl_with_collate_expr3 ((c1::STRING COLLATE en_US) ASC)
+                  )
+
+subtest end