Ignore permisison errors creating Snowflake schema

Update the Snowflake registry creation scripts to ignore permission
errors when creating or commenting on the registry schema, to account
for the case where the schema already exists but the current user does
not have permission to execute `CREATE SCHEMA`. Suggested by Peter
Wimsey (resolves #826).

Changes

@@ -30,6 +30,11 @@ Revision history for Perl extension App::Sqitch
        Exasol and because `FAILURE` maps to exit code `1`, which has in the
        past been more akin to a warning from Sqitch. Thanks to @vectro for the
        report (#831).
+     - Updated the Snowflake registry creation scripts to ignore permission
+       errors when creating or commenting on the registry schema, to account
+       for the case where the schema already exists but the current user does
+       not have permission to execute `CREATE SCHEMA`. Suggested by Peter
+       Wimsey (#826).
 
 1.4.1  2024-02-04T16:35:32Z
      - Removed the quoting of the role and warehouse identifiers that was

lib/App/Sqitch/Engine/Upgrade/snowflake-1.0.sql

@@ -19,4 +19,10 @@ UPDATE &registry.changes SET script_hash = change_id;
 ALTER TABLE &registry.changes ADD UNIQUE(script_hash);
 COMMENT ON COLUMN &registry.changes.script_hash IS 'Deploy script SHA-1 hash.';
 
-COMMENT ON SCHEMA &registry IS 'Sqitch database deployment metadata v1.0.';
+EXECUTE IMMEDIATE $$
+BEGIN
+    COMMENT ON SCHEMA &registry IS 'Sqitch database deployment metadata v1.0.';
+EXCEPTION WHEN statement_error THEN
+    IF (sqlstate = '42501') THEN RETURN ''; END IF;
+END;
+$$;

lib/App/Sqitch/Engine/Upgrade/snowflake-1.1.sql

@@ -1,3 +1,9 @@
 ALTER TABLE &registry.changes DROP UNIQUE(script_hash);
 ALTER TABLE &registry.changes ADD UNIQUE(project, script_hash);
-COMMENT ON SCHEMA &registry IS 'Sqitch database deployment metadata v1.0.';
+EXECUTE IMMEDIATE $$
+BEGIN
+    COMMENT ON SCHEMA &registry IS 'Sqitch database deployment metadata v1.1.';
+EXCEPTION WHEN statement_error THEN
+    IF (sqlstate = '42501') THEN RETURN ''; END IF;
+END;
+$$;

lib/App/Sqitch/Engine/snowflake.sql

@@ -1,6 +1,12 @@
-CREATE SCHEMA IF NOT EXISTS &registry;
-
-COMMENT ON SCHEMA &registry IS 'Sqitch database deployment metadata v1.1.';
+-- Create the schema but ignore permission errors
+EXECUTE IMMEDIATE $$
+BEGIN
+    CREATE SCHEMA IF NOT EXISTS identifier('&registry');
+    COMMENT ON SCHEMA identifier('&registry') IS 'Sqitch database deployment metadata v1.1.';
+EXCEPTION WHEN statement_error THEN
+    IF (sqlstate = '42501') THEN RETURN ''; END IF;
+END;
+$$;
 
 CREATE TABLE &registry.releases (
     version           FLOAT        PRIMARY KEY,