By default, don't rebuild apps if the SDK changes

Rebuilding all apps because a minor change in the runtime is way too wasteful
and generated unnecessary app updates, especially since runtimes are supposed
to be API stable.

We add an a --rebuild-on-sdk-change option which you use to disable this feature,
for instance if you're building against an unstable SDK.

builder/builder-context.c

@@ -58,6 +58,7 @@ struct BuilderContext
   gboolean        build_extension;
   gboolean        separate_locales;
   gboolean        sandboxed;
+  gboolean        rebuild_on_sdk_change;
 };
 
 typedef struct
@@ -389,6 +390,19 @@ builder_context_set_separate_locales (BuilderContext *self,
   self->separate_locales = !!separate_locales;
 }
 
+gboolean
+builder_context_get_rebuild_on_sdk_change (BuilderContext *self)
+{
+  return self->rebuild_on_sdk_change;
+}
+
+void
+builder_context_set_rebuild_on_sdk_change (BuilderContext *self,
+                                           gboolean        rebuild_on_sdk_change)
+{
+  self->rebuild_on_sdk_change = !!rebuild_on_sdk_change;
+}
+
 gboolean
 builder_context_enable_ccache (BuilderContext *self,
                                GError        **error)

builder/builder-context.h

@@ -76,6 +76,9 @@ void            builder_context_set_build_extension (BuilderContext *self,
 gboolean        builder_context_get_separate_locales (BuilderContext *self);
 void            builder_context_set_separate_locales (BuilderContext *self,
                                                       gboolean        separate_locales);
+gboolean        builder_context_get_rebuild_on_sdk_change (BuilderContext *self);
+void            builder_context_set_rebuild_on_sdk_change (BuilderContext *self,
+                                                           gboolean        rebuild_on_sdk_change);
 
 BuilderContext *builder_context_new (GFile *base_dir,
                                      GFile *app_dir);

builder/builder-main.c

@@ -47,6 +47,7 @@ static gboolean opt_keep_build_dirs;
 static gboolean opt_force_clean;
 static gboolean opt_allow_missing_runtimes;
 static gboolean opt_sandboxed;
+static gboolean opt_rebuild_on_sdk_change;
 static char *opt_stop_at;
 static char *opt_arch;
 static char *opt_repo;
@@ -81,6 +82,7 @@ static GOptionEntry entries[] = {
   { "sandbox", 0, 0, G_OPTION_ARG_NONE, &opt_sandboxed, "Enforce sandboxing, disabling build-args", NULL },
   { "stop-at", 0, 0, G_OPTION_ARG_STRING, &opt_stop_at, "Stop building at this module (implies --build-only)", "MODULENAME"},
   { "jobs", 0, 0, G_OPTION_ARG_INT, &opt_jobs, "Number of parallel jobs to build (default=NCPU)", "JOBS"},
+  { "rebuild-on-sdk-change", 0, 0, G_OPTION_ARG_NONE, &opt_rebuild_on_sdk_change, "Rebuild if sdk changes", NULL },
   { NULL }
 };
 
@@ -324,6 +326,7 @@ main (int    argc,
   builder_context_set_keep_build_dirs (build_context, opt_keep_build_dirs);
   builder_context_set_sandboxed (build_context, opt_sandboxed);
   builder_context_set_jobs (build_context, opt_jobs);
+  builder_context_set_rebuild_on_sdk_change (build_context, opt_rebuild_on_sdk_change);
 
   if (opt_arch)
     builder_context_set_arch (build_context, opt_arch);

builder/builder-manifest.c

@@ -1274,7 +1274,10 @@ builder_manifest_checksum (BuilderManifest *self,
   builder_cache_checksum_str (cache, self->runtime);
   builder_cache_checksum_str (cache, builder_manifest_get_runtime_version (self));
   builder_cache_checksum_str (cache, self->sdk);
-  builder_cache_checksum_str (cache, self->sdk_commit);
+  /* Always rebuild on sdk change if we're actually including the sdk in the cache */
+  if (self->writable_sdk || self->build_runtime ||
+      builder_context_get_rebuild_on_sdk_change (context))
+    builder_cache_checksum_str (cache, self->sdk_commit);
   builder_cache_checksum_str (cache, self->var);
   builder_cache_checksum_str (cache, self->metadata);
   builder_cache_checksum_strv (cache, self->tags);

doc/flatpak-builder.xml

@@ -822,6 +822,16 @@
                 </para></listitem>
             </varlistentry>
 
+            <varlistentry>
+                <term><option>--rebuild-on-sdk-change</option></term>
+
+                <listitem><para>
+                  Record the exact version of the sdk in the cache, and rebuild everything
+                  if it changes. This is useful if you're building against an API-unstable
+                  runtime, like a nightly build.
+                </para></listitem>
+            </varlistentry>
+
           </variablelist>
     </refsect1>