Ticket #1604 (closed task: wontfix)
Coarse-grained recompilation checking
|Reported by:||simonmar||Owned by:|
|Type of failure:||Difficulty:||Unknown|
|Test Case:||Blocked By:|
Description (last modified by simonmar) (diff)
GHC's recompilation checker is very clever: it tracks changes at the level of an individual function or type, and only recompiles a module when the entities it actually depends on have changed.
However, there are some drawbacks to doing this:
- It is complicated and hard to get right
- It adds extra information to .hi files
- It takes time to check the dependencies (probably not much, though)
- we have virtually no tests for it
- when it goes wrong, the bug is very hard to reproduce, which means that failures are often not reported.
So we propose:
- Simplify the recompilation checker so that it tracks changes at the level of a module only. This will cause more recompilation, but it will be much easier to get right and to test.
- As an intermediate step, we could implement both schemes and generate some output to indicate when they give different results.
See Commentary/Compiler/RecompilationAvoidance for more discussion.