Database: add metadata with the version number of the database layout…

… and check it in the code

This is aimed at detecting running a PROJ version against a proj.db that is not
meant to work with it. This happens sometimes in complex setups mixing PROJ
versions. Hopefully this will help spotting the issue earlier.

data/sql/metadata.sql

@@ -1,2 +1,13 @@
+-- Version of the database structure.
+-- The major number indicates an incompatible change (e.g. table or column
+-- removed or renamed).
+-- The minor number is incremented if a backward compatible change done, that
+-- is the new database can still work with an older PROJ version.
+-- When updating those numbers, the DATABASE_LAYOUT_VERSION_MAJOR and
+-- DATABASE_LAYOUT_VERSION_MINOR constants in src/iso19111/factory.cpp must be
+-- updated as well.
+INSERT INTO "metadata" VALUES('DATABASE.LAYOUT.VERSION.MAJOR', 1);
+INSERT INTO "metadata" VALUES('DATABASE.LAYOUT.VERSION.MINOR', 0);
+
 INSERT INTO "metadata" VALUES('EPSG.VERSION', 'v10.007');
 INSERT INTO "metadata" VALUES('EPSG.DATE', '2020-11-18');

src/iso19111/factory.cpp

@@ -93,6 +93,12 @@ namespace io {
 #define GEOG_3D_SINGLE_QUOTED "'geographic 3D'"
 #define GEOCENTRIC_SINGLE_QUOTED "'geocentric'"
 
+// See data/sql/metadata.sql for the semantics of those constants
+constexpr int DATABASE_LAYOUT_VERSION_MAJOR = 1;
+// If the code depends on the new additions, then DATABASE_LAYOUT_VERSION_MINOR
+// must be incremented.
+constexpr int DATABASE_LAYOUT_VERSION_MINOR = 0;
+
 // ---------------------------------------------------------------------------
 
 struct SQLValues {
@@ -277,6 +283,8 @@ struct DatabaseContext::Private {
     lru11::Cache<std::string, std::list<std::string>> cacheAliasNames_{
         CACHE_SIZE};
 
+    void checkDatabaseLayout();
+
     static void insertIntoCache(LRUCacheOfObjects &cache,
                                 const std::string &code,
                                 const util::BaseObjectPtr &obj);
@@ -571,6 +579,59 @@ void DatabaseContext::Private::open(const std::string &databasePath,
 
 // ---------------------------------------------------------------------------
 
+void DatabaseContext::Private::checkDatabaseLayout() {
+    auto res = run("SELECT key, value FROM metadata WHERE key IN "
+                   "('DATABASE.LAYOUT.VERSION.MAJOR', "
+                   "'DATABASE.LAYOUT.VERSION.MINOR')");
+    if (res.size() != 2) {
+        // The database layout of PROJ 7.2 that shipped with EPSG v10.003 is
+        // at the time of writing still compatible of the one we support.
+        static_assert(
+            DATABASE_LAYOUT_VERSION_MAJOR == 1 &&
+                DATABASE_LAYOUT_VERSION_MINOR == 0,
+            "remove that assertion and below lines next time we upgrade "
+            "database structure");
+        res = run("SELECT 1 FROM metadata WHERE key = 'EPSG.VERSION' AND "
+                  "value = 'v10.003'");
+        if (!res.empty()) {
+            return;
+        }
+
+        throw FactoryException(
+            databasePath_ +
+            " lacks DATABASE.LAYOUT.VERSION.MAJOR / "
+            "DATABASE.LAYOUT.VERSION.MINOR "
+            "metadata. It comes from another PROJ installation.");
+    }
+    int nMajor = 0;
+    int nMinor = 0;
+    for (const auto &row : res) {
+        if (row[0] == "DATABASE.LAYOUT.VERSION.MAJOR") {
+            nMajor = atoi(row[1].c_str());
+        } else if (row[0] == "DATABASE.LAYOUT.VERSION.MINOR") {
+            nMinor = atoi(row[1].c_str());
+        }
+    }
+    if (nMajor != DATABASE_LAYOUT_VERSION_MAJOR) {
+        throw FactoryException(databasePath_ +
+                               " contains DATABASE.LAYOUT.VERSION.MAJOR = " +
+                               toString(nMajor) + " whereas " +
+                               toString(DATABASE_LAYOUT_VERSION_MAJOR) +
+                               " is expected. "
+                               "It comes from another PROJ installation.");
+    }
+    if (nMinor < DATABASE_LAYOUT_VERSION_MINOR) {
+        throw FactoryException(databasePath_ +
+                               " contains DATABASE.LAYOUT.VERSION.MINOR = " +
+                               toString(nMinor) + " whereas a number >= " +
+                               toString(DATABASE_LAYOUT_VERSION_MINOR) +
+                               " is expected. "
+                               "It comes from another PROJ installation.");
+    }
+}
+
+// ---------------------------------------------------------------------------
+
 void DatabaseContext::Private::setHandle(sqlite3 *sqlite_handle) {
 
     assert(sqlite_handle);
@@ -888,6 +949,7 @@ DatabaseContext::create(const std::string &databasePath,
     if (!auxiliaryDatabasePaths.empty()) {
         dbCtx->getPrivate()->attachExtraDatabases(auxiliaryDatabasePaths);
     }
+    dbCtx->getPrivate()->checkDatabaseLayout();
     return dbCtx;
 }