Please document what substitutions are available in rule outputs

[zrlk]

In the outputs of a rule, %{name} does something; %{src} also appears to do something, but I can't find this documented anywhere. What's the context in which these are evaluated? Can I write expressions or just variable lookups?

[laszlocsomor]

AFAIK that's only supposed to work in a few attributes and it should be documented in the BE. Which rule and attribute name did you try? Can you tell more about what %{src} seems to do?

[ulfbot]

You can basically refer to any attribute, no expressions. However,
referring to anything other than %{name} is likely to run into problems,
because these templates are evaluated at loading time, at which point we
don't have full information about the attributes yet - things like select()
and filegroup make this hard.

If you are writing a built-in (native) rule, you can subclass
ImplicitOutputsFunction with custom code. If you don't need to be able to
refer to the files by name in another rule, then you don't need to use this
at all; you can just generate file names as you wish. However, you need to
make sure that you don't get name conflicts with other rules in the same
package.

It would be good if you could tell us what you're trying to do.

On Tue, Apr 14, 2015 at 9:37 AM, László Csomor [email protected]
wrote:

AFAIK that's only supposed to work in a few attributes and it should be
documented in the BE. Which rule and attribute name did you try? Can you
tell more about what %{src} seems to do?

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#115 (comment).

[hanwen]

this commit expanded what %{attr} expansions are available: 6c8b0b6

Let's use this issue for the missing documentation.

@zrlk - can you open a separate issue if there is functionality you are missing?

[hanwen]

Laurent, can you make the rule() documentation point to the relevant part of the BE, and/or document any other limitations on naming outputs?

[laurentlb]

Won't fix: this feature is now deprecated (#6241).