[GitHub] ccollins476ad opened a new issue #233: Circular dependencies may cause extraneous packages to get pulled into build

[GitBox <gi...@apache.org>]

ccollins476ad opened a new issue #233: Circular dependencies may cause extraneous packages to get pulled into build
URL: https://github.com/apache/mynewt-newt/issues/233
 
 
   During dependency resolution, newt adds packages to the builds as dependencies are discovered.  Less commonly, newt also removes packages from the build when a dependency is nullified.  When a syscfg setting's value changes, dependencies conditional on the setting may be nullified.  For example:
   
   #### Package A
   ```
   # pkg.yml
   pkg.deps:
       - pkgb
   ```
   
   #### Target
   ```
   # syscfg.yml
   syscfg.vals:
       FOO: 1
   ```
   
   Initially, the `FOO` setting is unknown, so it defaults to 0.  When package A is being processed, the conditional dependency on package B is considered valid, and B is added to the build.  When the target is processed, it is discovered that `FOO` is actually 1, so A's dependency on B is nullified, and B must be removed from the build (assuming no other packages depend on B).
   
   Newt handles the above case without issue.  The issue is illustrated below:
   
   #### Package B
   ```
   # pkg.yml
   pkg.deps:
       - pkgc
   ```
   
   #### Package C
   ```
   # pkg.yml
   pkg.deps:
       - pkgb
   ```
   
   B and C depend on each other.  When B is initially pulled into the build, this also pulls in C, since B depends on C.  When B is later removed from the build, C should also get removed (again, assuming no other packages depend on C).
   
   The bug is: in this example, neither B nor C actually gets removed from the build.  Newt uses references counting to determine when a package can be removed.  When a package is found to have no dependents (a reference count of 0), newt removes it.  Due to the circular dependency between B and C, neither package's reference count ever reaches 0.

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