[question] Why tool_requires cannot be indexed from self dependencies?

[Adnn]

What is your question?

We found a behaviour that surprised us (Conan 2.5.0 on Windows):

self.dependencies, when iterated via items() or values(), contains all dependencies (which is consistent with the documentation).

Yet, when indexing via operator[] and the upstream name (such self.dependencies["upstream"]), the host requirements are found, but not the tool (build) requirements. Tool requirements can only be indexed on self.dependencies.build.

Is it an expected behaviour?

[memsharded]

Hi @Adnn

yes, this is expected and by design. We found that the use case of having the same dependency both as requires and tool_requires is relatively common, and as it is not possible to disambiguate the 2 different dependencies in a single self.dependencies["mydep"], there was the option of raising an error like KeyError-like about having 2 different dependencies with the same name.

But then, it is also possible to inject [tool_requires] from profiles, that could mean in some occassions that a code that was valid in a recipe for self.dependencies["mydep"] was suddenly crashing due to the injected requirement. But it was "evident" from the point of view of the recipe writer that such expression should always refer to the "host" dependency and not the build one.

Furthermore, the use case for accessing directly tool-requires dependencies from the self.dependencies interface was very low compared to the one of accessing host dependencies.

So we decided to use that behavior, the self.dependencies[] operator works exclusively for host dependencies, not build, and if users want to directly access build dependencies self.dependencies.build[] is necessary. I understand it might be surprising in some cases, but we have found that it works pretty nicely for the majority of cases.

[Adnn]

Thank you @memsharded for this detailed explanation, this clears things up!