gi: Roll back change to imports.gi.versions object if gi.require() fails

If something like gi.require('GLib', '1.75') fails, then we don't want the
faulty version number remaining on the imports.gi.versions object.

2 files changed, 19 insertions, 6 deletions

diff --git a/installed-tests/js/testESModules.js b/installed-tests/js/testESModules.js
index 30db17e4..e727c790 100644
--- a/installed-tests/js/testESModules.js
+++ b/installed-tests/js/testESModules.js
@@ -27,26 +27,32 @@ describe('ES module imports', function () {
 
     it('import with version parameter', function () {
         expect(gi.require('GObject', '2.0')).toBe(gi.require('GObject'));
+        expect(imports.gi.versions['GObject']).toBe('2.0');
     });
 
     it('import again with other version parameter', function () {
         expect(() => gi.require('GObject', '1.75')).toThrow();
+        expect(imports.gi.versions['GObject']).toBe('2.0');
     });
 
     it('import for the first time with wrong version', function () {
         expect(() => gi.require('Gtk', '1.75')).toThrow();
+        expect(imports.gi.versions['Gtk']).not.toBeDefined();
     });
 
     it('import with another version after a failed import', function () {
         expect(gi.require('Gtk', '3.0').toString()).toEqual('[object GIRepositoryNamespace]');
+        expect(imports.gi.versions['Gtk']).toBe('3.0');
     });
 
     it('import nonexistent module', function () {
         expect(() => gi.require('PLib')).toThrow();
+        expect(imports.gi.versions['PLib']).not.toBeDefined();
     });
 
     it('GObject introspection import via URL scheme', function () {
         expect(Gio.toString()).toEqual('[object GIRepositoryNamespace]');
+        expect(imports.gi.versions['Gio']).toBe('2.0');
     });
 
     it('import.meta.url', function () {
diff --git a/modules/esm/gi.js b/modules/esm/gi.js
index 126ce7e7..b49cf120 100644
--- a/modules/esm/gi.js
+++ b/modules/esm/gi.js
@@ -8,17 +8,24 @@ const Gi = {
         if (namespace === 'versions')
             throw new Error('Cannot import namespace "versions", use the version parameter of Gi.require to specify versions.');
 
+        let oldVersion = gi.versions[namespace];
         if (version !== undefined)
             gi.versions[namespace] = version;
 
-        const module = gi[namespace];
+        try {
+            const module = gi[namespace];
 
-        if (version !== undefined && version !== module.__version__) {
-            throw new Error(`Version ${module.__version__} of GI module ${
-                namespace} already loaded, cannot load version ${version}`);
-        }
+            if (version !== undefined && version !== module.__version__) {
+                throw new Error(`Version ${module.__version__} of GI module ${
+                    namespace} already loaded, cannot load version ${version}`);
+            }
 
-        return module;
+            return module;
+        } catch (error) {
+            // Roll back change to versions object if import failed
+            gi.versions[namespace] = oldVersion;
+            throw error;
+        }
     },
 };
 Object.freeze(Gi);