Changes between Version 18 and Version 19 of Commentary/Compiler/RecompilationAvoidance

Timestamp:

02/17/10 05:26:52 (3 years ago)

Author:

simonmar

Comment:

Add "package version changes"

Commentary/Compiler/RecompilationAvoidance

@@ -167 +167 @@
    * The ''ABI hash'', which depends on everything that the module
      exposes about its implementation: think of this as a hash of
-     ''exports'' and ''decls''.
+     ''export-list hash'' and ''decls''.
    * The ''export-list hash'', which depends on the contents of the
-     export list (a hash of ''exports'').
+     export list (a hash of ''exports''), the ''orphan hash'' (see [#Orphans Orphans]) and the package dependencies (see [#Packageversionchanges Package Version Changes]).
    * The ''orphan hash'', which depends on all the orphan
      instances/rules in the, and the orphan hashes of all orphan
-     modules below this module in the dependency tree (see "Orphans"
-     later).
+     modules below this module in the dependency tree (see [#Orphans Orphans]).
  * ''exports'': what the module exports
  * ''dependencies'': modules and packages that this module depends on
@@ -551 +550 @@
 (Correctly triggering recompilation when packages change was one of the things we fixed when implementing fingerprints, see #1372).
 
+=== Package version changes ===
+
+If the version of a package is bumped, what forces recompilation of
+the things that depend on it?
+
+ 1. If a module from the package is imported directly, then we will notice that the imported module is not amongst the dependencies of the module when it was compiled last, and force a recompilation (see [#Decidingwhethertorecompile Deciding whether to recompile]).
+
+ 2. If a module from the old package is imported indirectly, then the old package will be amongst the package dependencies (`dep_pkgs . mi_deps`), so we must recompile otherwise these dependencies will be inconsistent.  The way we handle this case is by including the package dependencies in the ''export hash'' of a module, so that other modules which import this module will automatically be recompiled when one of the package dependencies changes.  The recompiled module will have new package dependencies, which will force recompilation of its importers, and so on.  Therefore if a package version changes, the change will be propagated throughout the module dependency graph.
+
 
 == Interface stability ==