1 files changed, 107 insertions, 1 deletions

diff --git a/lib/database-private.h b/lib/database-private.h
index d3e65fd6..ca0751cf 100644
--- a/lib/database-private.h
+++ b/lib/database-private.h
@@ -36,16 +36,106 @@
 
 #pragma GCC visibility push(hidden)
 
+/* Bit masks for _notmuch_database::features.  Features are named,
+ * independent aspects of the database schema.
+ *
+ * A database stores the set of features that it "uses" (implicitly
+ * before database version 3 and explicitly as of version 3).
+ *
+ * A given library version will "recognize" a particular set of
+ * features; if a database uses a feature that the library does not
+ * recognize, the library will refuse to open it.  It is assumed the
+ * set of recognized features grows monotonically over time.  A
+ * library version will "implement" some subset of the recognized
+ * features: some operations may require that the database use (or not
+ * use) some feature, while other operations may support both
+ * databases that use and that don't use some feature.
+ *
+ * On disk, the database stores string names for these features (see
+ * the feature_names array).  These enum bit values are never
+ * persisted to disk and may change freely.
+ */
+enum _notmuch_features {
+    /* If set, file names are stored in "file-direntry" terms.  If
+     * unset, file names are stored in document data.
+     *
+     * Introduced: version 1. */
+    NOTMUCH_FEATURE_FILE_TERMS = 1 << 0,
+
+    /* If set, directory timestamps are stored in documents with
+     * XDIRECTORY terms and relative paths.  If unset, directory
+     * timestamps are stored in documents with XTIMESTAMP terms and
+     * absolute paths.
+     *
+     * Introduced: version 1. */
+    NOTMUCH_FEATURE_DIRECTORY_DOCS = 1 << 1,
+
+    /* If set, the from, subject, and message-id headers are stored in
+     * message document values.  If unset, message documents *may*
+     * have these values, but if the value is empty, it must be
+     * retrieved from the message file.
+     *
+     * Introduced: optional in version 1, required as of version 3.
+     */
+    NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES = 1 << 2,
+
+    /* If set, folder terms are boolean and path terms exist.  If
+     * unset, folder terms are probabilistic and stemmed and path
+     * terms do not exist.
+     *
+     * Introduced: version 2. */
+    NOTMUCH_FEATURE_BOOL_FOLDER = 1 << 3,
+};
+
+/* In C++, a named enum is its own type, so define bitwise operators
+ * on _notmuch_features. */
+inline _notmuch_features
+operator|(_notmuch_features a, _notmuch_features b)
+{
+    return static_cast<_notmuch_features>(
+	static_cast<unsigned>(a) | static_cast<unsigned>(b));
+}
+
+inline _notmuch_features
+operator&(_notmuch_features a, _notmuch_features b)
+{
+    return static_cast<_notmuch_features>(
+	static_cast<unsigned>(a) & static_cast<unsigned>(b));
+}
+
+inline _notmuch_features
+operator~(_notmuch_features a)
+{
+    return static_cast<_notmuch_features>(~static_cast<unsigned>(a));
+}
+
+inline _notmuch_features&
+operator|=(_notmuch_features &a, _notmuch_features b)
+{
+    a = a | b;
+    return a;
+}
+
+inline _notmuch_features&
+operator&=(_notmuch_features &a, _notmuch_features b)
+{
+    a = a & b;
+    return a;
+}
+
 struct _notmuch_database {
     notmuch_bool_t exception_reported;
 
     char *path;
 
-    notmuch_bool_t needs_upgrade;
     notmuch_database_mode_t mode;
     int atomic_nesting;
     Xapian::Database *xapian_db;
 
+    /* Bit mask of features used by this database.  This is a
+     * bitwise-OR of NOTMUCH_FEATURE_* values (above). */
+    enum _notmuch_features features;
+
     unsigned int last_doc_id;
     uint64_t last_thread_id;
 
@@ -55,6 +145,22 @@ struct _notmuch_database {
     Xapian::ValueRangeProcessor *date_range_processor;
 };
 
+/* Prior to database version 3, features were implied by the database
+ * version number, so hard-code them for earlier versions. */
+#define NOTMUCH_FEATURES_V0 ((enum _notmuch_features)0)
+#define NOTMUCH_FEATURES_V1 (NOTMUCH_FEATURES_V0 | NOTMUCH_FEATURE_FILE_TERMS | \
+			     NOTMUCH_FEATURE_DIRECTORY_DOCS)
+#define NOTMUCH_FEATURES_V2 (NOTMUCH_FEATURES_V1 | NOTMUCH_FEATURE_BOOL_FOLDER)
+
+/* Current database features.  If any of these are missing from a
+ * database, request an upgrade.
+ * NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES is not included because
+ * upgrade doesn't currently introduce the feature (though brand new
+ * databases will have it). */
+#define NOTMUCH_FEATURES_CURRENT \
+    (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_DIRECTORY_DOCS | \
+     NOTMUCH_FEATURE_BOOL_FOLDER)
+
 /* Return the list of terms from the given iterator matching a prefix.
  * The prefix will be stripped from the strings in the returned list.
  * The list will be allocated using ctx as the talloc context.