odb/source: introduce function to map source type to name

Introduce a new function that maps an object source's type to a
human-readable name. Use the function to provide better human-readable
error messages for the downcasting functions.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

odb/source-files.h

@@ -28,7 +28,9 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 static inline struct odb_source_files *odb_source_files_downcast(struct odb_source *source)
 {
 	if (source->type != ODB_SOURCE_FILES)
-		BUG("trying to downcast source of type '%d' to files", source->type);
+		BUG("trying to downcast source of type '%s' to '%s'",
+		    odb_source_type_to_name(source->type),
+		    odb_source_type_to_name(ODB_SOURCE_FILES));
 	return container_of(source, struct odb_source_files, base);
 }
 

odb/source-inmemory.h

@@ -26,7 +26,9 @@ struct odb_source_inmemory *odb_source_inmemory_new(struct object_database *odb)
 static inline struct odb_source_inmemory *odb_source_inmemory_downcast(struct odb_source *source)
 {
 	if (source->type != ODB_SOURCE_INMEMORY)
-		BUG("trying to downcast source of type '%d' to in-memory", source->type);
+		BUG("trying to downcast source of type '%s' to '%s'",
+		    odb_source_type_to_name(source->type),
+		    odb_source_type_to_name(ODB_SOURCE_INMEMORY));
 	return container_of(source, struct odb_source_inmemory, base);
 }
 

odb/source-loose.h

@@ -41,7 +41,9 @@ struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
 static inline struct odb_source_loose *odb_source_loose_downcast(struct odb_source *source)
 {
 	if (source->type != ODB_SOURCE_LOOSE)
-		BUG("trying to downcast source of type '%d' to loose", source->type);
+		BUG("trying to downcast source of type '%s' to '%s'",
+		    odb_source_type_to_name(source->type),
+		    odb_source_type_to_name(ODB_SOURCE_LOOSE));
 	return container_of(source, struct odb_source_loose, base);
 }
 

odb/source-packed.h

@@ -78,7 +78,9 @@ struct odb_source_packed *odb_source_packed_new(struct object_database *odb,
 static inline struct odb_source_packed *odb_source_packed_downcast(struct odb_source *source)
 {
 	if (source->type != ODB_SOURCE_PACKED)
-		BUG("trying to downcast source of type '%d' to packed", source->type);
+		BUG("trying to downcast source of type '%s' to '%s'",
+		    odb_source_type_to_name(source->type),
+		    odb_source_type_to_name(ODB_SOURCE_PACKED));
 	return container_of(source, struct odb_source_packed, base);
 }
 

odb/source.c

@@ -4,6 +4,25 @@
 #include "odb/source.h"
 #include "packfile.h"
 
+static const char * const odb_source_names_by_type[] = {
+	[ODB_SOURCE_UNKNOWN] = "unknown",
+	[ODB_SOURCE_FILES] = "files",
+	[ODB_SOURCE_LOOSE] = "loose",
+	[ODB_SOURCE_PACKED] = "packed",
+	[ODB_SOURCE_INMEMORY] = "inmemory",
+};
+
+const char *odb_source_type_to_name(enum odb_source_type type)
+{
+	const char *name;
+	if (type < 0 || type >= ARRAY_SIZE(odb_source_names_by_type))
+		type = ODB_SOURCE_UNKNOWN;
+	name = odb_source_names_by_type[type];
+	if (!name)
+		BUG("name missing in `odb_source_names_by_type` for '%d'", type);
+	return name;
+}
+
 struct odb_source *odb_source_new(struct object_database *odb,
 				  const char *path,
 				  bool local)

odb/source.h

@@ -25,6 +25,12 @@ enum odb_source_type {
 	ODB_SOURCE_INMEMORY,
 };
 
+/*
+ * Convert between the enum and its name. Returns the equivalent of "unknown"
+ * for unknown types.
+ */
+const char *odb_source_type_to_name(enum odb_source_type type);
+
 struct object_id;
 struct odb_read_stream;
 struct strvec;