Tab-complete CREATE COLLATION.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com

src/bin/psql/tab-complete.c

@@ -609,6 +609,14 @@ static const SchemaQuery Query_for_list_of_statistics = {
 	.result = "pg_catalog.quote_ident(s.stxname)",
 };
 
+static const SchemaQuery Query_for_list_of_collations = {
+	.catname = "pg_catalog.pg_collation c",
+	.selcondition = "c.collencoding IN (-1, pg_catalog.pg_char_to_encoding(pg_catalog.getdatabaseencoding()))",
+	.viscondition = "pg_catalog.pg_collation_is_visible(c.oid)",
+	.namespace = "c.collnamespace",
+	.result = "pg_catalog.quote_ident(c.collname)",
+};
+
 
 /*
  * Queries to get lists of names of various kinds of things, possibly
@@ -1031,7 +1039,7 @@ static const pgsql_thing_t words_after_create[] = {
 	{"AGGREGATE", NULL, NULL, Query_for_list_of_aggregates},
 	{"CAST", NULL, NULL, NULL}, /* Casts have complex structures for names, so
 								 * skip it */
-	{"COLLATION", "SELECT pg_catalog.quote_ident(collname) FROM pg_catalog.pg_collation WHERE collencoding IN (-1, pg_catalog.pg_char_to_encoding(pg_catalog.getdatabaseencoding())) AND substring(pg_catalog.quote_ident(collname),1,%d)='%s'"},
+	{"COLLATION", NULL, NULL, &Query_for_list_of_collations},
 
 	/*
 	 * CREATE CONSTRAINT TRIGGER is not supported here because it is designed
@@ -2433,6 +2441,22 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("CREATE", "ACCESS", "METHOD", MatchAny, "TYPE", MatchAny))
 		COMPLETE_WITH("HANDLER");
 
+	/* CREATE COLLATION */
+	else if (Matches("CREATE", "COLLATION", MatchAny))
+		COMPLETE_WITH("(", "FROM");
+	else if (Matches("CREATE", "COLLATION", MatchAny, "FROM"))
+		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_collations, NULL);
+	else if (HeadMatches("CREATE", "COLLATION", MatchAny, "(*"))
+	{
+		if (TailMatches("(|*,"))
+			COMPLETE_WITH("LOCALE =", "LC_COLLATE =", "LC_CTYPE =",
+						  "PROVIDER =", "DETERMINISTIC =");
+		else if (TailMatches("PROVIDER", "="))
+			COMPLETE_WITH("libc", "icu");
+		else if (TailMatches("DETERMINISTIC", "="))
+			COMPLETE_WITH("true", "false");
+	}
+
 	/* CREATE DATABASE */
 	else if (Matches("CREATE", "DATABASE", MatchAny))
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",