Update custom composer package fails if the packages require each other - php

Question

I am working with multiple composer packages as a library and sometimes those packages require each other. For example, in modolib/phpunit I have:
"require": {
"modolib/doctrine": "~1.2",
}
and in the package modolib/doctrine I have:
"require-dev": {
// ...
"modolib/phpunit": "~1.3"
},
To version the packages, I use tags. Calling git tag for modolib/phpunit in branch master puts out:
// ...
1.2.8
1.2.9
1.2.10
1.3.0
1.3.1
// ...
1.3.10
and git tag for modolib/doctrine at branch master puts out:
// ...
1.2.8
1.2.9
1.2.10
1.2.11
1.2.12
However, a composer update in modolib/phpunit will perfectly work, but an update in modolib/doctrine will throw this error:
Problem 1
- modolib/phpunit 1.3.9 requires moodlib/doctrine ~1.2 -> no matching packages found
- modolib/phpunit 1.3.8 requires moodlib/doctrine ~1.2 -> no matching packages found
- modolib/phpunit 1.3.7 requires moodlib/doctrine ~1.2 -> no matching packages found
- modolib/phpunit 1.3.5 requires moodlib/doctrine 1.2.* -> no matching packages found
- modolib/phpunit 1.3.4 requires moodlib/doctrine 1.2.* -> no matching packages found
- modolib/phpunit 1.3.3 requires moodlib/doctrine 1.2.* -> no matching packages found
- modolib/phpunit 1.3.2 requires moodlib/doctrine 1.2.* -> no matching packages found
- modolib/phpunit 1.3.10 requires moodlib/doctrine 1.*.* -> no matching packages found
- modolib/phpunit 1.3.1 requires moodlib/doctrine 1.2.* -> no matching packages found
- modolib/phpunit 1.3.0 requires moodlib/doctrine 1.2.* -> no matching packages found
- Installation request for modolib/phpunit ~1.3 -> satisfiable by modolib/phpunit[1.3.0, 1.3.1, 1.3.10, 1.3.2, 1.3.3, 1.3.4, 1.3.5, 1.3.7, 1.3.8, 1.3.9]
The current version of modolib/doctrine is 1.2.12 and no commits have been added since I created this tag except for the merge to master (I am using git flow).
Now it seems like the expression "modolib/doctrine": "~1.2" is correct, since I can update the packages in modolib/phpunit itself, but the composer has problems with noticing I am working in the package it is trying to request. Or could it have something to do with the difference between require and require-dev?
How can I solve this error and update my packages in modolib/doctrine?
UPDATE:
The reason why the update in modolib/phpunit worked is because modolib/doctrine requires modolib/phpunit in require-dev, but the composer does not load the require-dev sections of the packages it's loading during the update. Therefore, from the view of modolib/phpunit the packages do not require each other. Only modolib/doctrine is loaded, but it does not try to load modolib/phpunit while working in this repository.

Answer 1

The composer does notice if the requirement is the package you are currently working in. What it does not notice is the tagged version. Of course Composer can not read your repository tags, so you need to provide them in the composer.json:
"name": "modolib/doctrine",
"version": "1.2.12",
// ...
"require-dev": {
// ...
"modolib/phpunit": "~1.3"
},
Now composer knows both name and version of your package and can validate the dependency.