feat: validate schema hash before running tests

Author: radim

regresql/regresql.go

@@ -155,6 +155,12 @@ func Test(root, runFilter, formatName, outputPath string, commit bool) {
 	// Cache config for plan quality analysis
 	SetGlobalConfig(config)
 
+	// Validate schema hasn't changed since last snapshot build
+	if err := ValidateSchemaHash(root); err != nil {
+		fmt.Printf("Error: %s\n", err)
+		os.Exit(1)
+	}
+
 	if err := TestConnectionString(config.PgUri); err != nil {
 		fmt.Print(err.Error())
 		os.Exit(2)

regresql/snapshot.go

@@ -490,3 +490,49 @@ func DetectSnapshotFormat(path string) SnapshotFormat {
 
 	return FormatCustom
 }
+
+func computeSchemaHash(schemaPath string) (string, error) {
+	format := DetectSnapshotFormat(schemaPath)
+	return computeFileHash(schemaPath, format)
+}
+
+func ValidateSchemaHash(root string) error {
+	snapshotsDir := GetSnapshotsDir(root)
+
+	metadata, err := ReadSnapshotMetadata(snapshotsDir)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Warning: no snapshot metadata found. Consider using 'regresql snapshot build' for reproducible tests.\n")
+		return nil
+	}
+
+	if metadata.Current == nil || metadata.Current.SchemaPath == "" {
+		return nil
+	}
+
+	// Check if schema file still exists
+	if _, err := os.Stat(metadata.Current.SchemaPath); os.IsNotExist(err) {
+		// Schema file referenced in metadata doesn't exist - stale metadata
+		return nil
+	}
+
+	currentHash, err := computeSchemaHash(metadata.Current.SchemaPath)
+	if err != nil {
+		return fmt.Errorf("failed to hash schema %s: %w", metadata.Current.SchemaPath, err)
+	}
+
+	if currentHash != metadata.Current.SchemaHash {
+		return fmt.Errorf(`schema has changed since last snapshot build
+
+  Schema file: %s
+  Expected:    %s
+  Current:     %s
+
+Run 'regresql snapshot build --schema=%s' to rebuild the snapshot`,
+			metadata.Current.SchemaPath,
+			metadata.Current.SchemaHash[:20]+"...",
+			currentHash[:20]+"...",
+			metadata.Current.SchemaPath)
+	}
+
+	return nil
+}

regresql/snapshot_build.go

@@ -181,11 +181,6 @@ func execSQLFile(db *sql.DB, path string) error {
 	return nil
 }
 
-func computeSchemaHash(schemaPath string) (string, error) {
-	format := DetectSnapshotFormat(schemaPath)
-	return computeFileHash(schemaPath, format)
-}
-
 func applySchemaFile(pguri, schemaPath string) error {
 	format := DetectSnapshotFormat(schemaPath)