Our current configuration logic is completely oblivious of any repository, but only cares for actual file paths. Unfortunately, we are forced to break this assumption by the introduction of conditional includes, which are evaluated in the context of a repository. Right now, only one conditional exists with "gitdir:" -- it will only include the configuration if the current repository's git directory matches the value passed to "gitdir:". To support these conditionals, we have to break our API and make the repository available when opening a configuration file. This commit extends the `open` call of configuration backends to include another repository and adjusts existing code to have it available. This includes the user-visible functions `git_config_add_file_ondisk` and `git_config_add_backend`.
While it is technically possible to look up submodules inside of a bare repository by reading the submodule configuration of a specific commit, we do not offer this functionality right now. As such, calling both `git_submodule_lookup` and `git_submodule_foreach` should error out early when these functions encounter a bare repository. While `git_submodule_lookup` already does return an error due to not being able to parse the configuration, `git_submodule_foreach` simply returns success and never invokes the callback function. Fix the issue by having both functions check whether the repository is bare and returning an error in that case.
Next to including several files, our "common.h" header also declares various macros which are then used throughout the project. As such, we have to make sure to always include this file first in all implementation files. Otherwise, we might encounter problems or even silent behavioural differences due to macros or defines not being defined as they should be. So in fact, our header and implementation files should make sure to always include "common.h" first. This commit does so by establishing a common include pattern. Header files inside of "src" will now always include "common.h" as its first other file, separated by a newline from all the other includes to make it stand out as special. There are two cases for the implementation files. If they do have a matching header file, they will always include this one first, leading to "common.h" being transitively included as first file. If they do not have a matching header file, they instead include "common.h" as first file themselves. This fixes the outlined problems and will become our standard practice for header and source files inside of the "src/" from now on.
Worktree fixes
It is possible to specify submodule URLs relative to the repository location. E.g. having a submodule with URL "../submodule" will look for the submodule at "repo/../submodule". With the introduction of worktrees, though, we cannot simply resolve the URL relative to the repository location itself. If the repository for which a URL is to be resolved is a working tree, we have to resolve the URL relative to the parent's repository path. Otherwise, the URL would change depending on where the working tree is located. Fix this by special-casing when we have a working tree while getting the URL base.
When calling `git_submodule_update` on a submodule, we have to retrieve the ID of the submodule entry in the index. If the function is called on a submodule which is only partly initialized, the submodule entry may not be added to the index yet. This leads to an assert when trying to look up the blob later on. Fix the issue by checking if the index actually holds the submodule's ID and erroring out if it does not.
The recent introduction of the commondir variable of a repository requires callers to distinguish whether their files are part of the dot-git directory or the common directory shared between multpile worktrees. In order to take the burden from callers and unify knowledge on which files reside where, the `git_repository_item_path` function has been introduced which encapsulate this knowledge. Modify most existing callers of `git_repository_path` to use `git_repository_item_path` instead, thus making them implicitly aware of the common directory.