Add a hook triggered before each run of P4 command

[thekondor]

Motivation: be able to run project's configuration commands before P4 command is executed.
Example:

• Automatically deduce current workspace (e.g. based on buffer's directory) and set ${P4CLIENT} environment variable up;
• Keep a history of run P4 commands.

[gareth-rees]

1. It's already possible to work with multiple client workspaces by setting the P4CONFIG environment variable and putting a configuration file in each workspace. This mechanism has the advantage of being supported by Perforce, and it works from the shell, or from P4V, whereas a hook function in Emacs only works inside Emacs. Can you explain why P4CONFIG doesn't work for you?
2. Can you explain why you need a history of Perforce commands?
3. There's already a hook p4-modify-args-function which is called every time the p4 client is run. You could supply a function that modifies the arguments to add the appropriate -c flag to override the client workspace, or that saves the arguments in a history list. Can you explain why this doesn't work for your use case?

[thekondor]

Hi,

• I am fully aware of P4CONFIG, and it works like a charm when there is not too many active workspaces. Due to the environment I might have at least 10 active workspaces per day; they also can belong to various Perforce servers (actually, the difference goes by TCP ports, but doesn't matter). Maintenance of P4CONFIG becomes a bit tedious; it is much easier to have a script that deduces a right workspace for you to set the right P4CLIENT up.
• In the case of similar merges in several workspaces. But that is a minor case for me, just an example of the possible usage. The main case is n.1.
• As far as I remember, p4-modify-args-function does work in the context of newly created buffer intended for p4 command output. So there is no way to get a full path of the target buffer. I will be happy if I am wrong at this point, please correct me.