Add b4 Tool

[adityagesh]

Add b4 tool to download upstream patches.
Add am method to git in order to apply this patch.

The usage of these will be raised as a separate PR. A new modifier will be added to kernel_installer to modify code using b4.

[LiliDeng]

does git am depend on b4 package?

[adityagesh]

The output of b4 is a .mbx file. You can apply this patch to the repo using git am "filename.mbx"

As per description, git am can be used to apply any email related patch, whereas git apply is for the .patch files

[LiliDeng]

I didn't see the place which uses b4 tool

[adityagesh]

I will be raising that as a separate PR, added that in the description.
I have created a Modifier in Kernel Install transformer that uses b4 to apply patches

[adityagesh]

I can add those changes to this PR, if you prefer having it in the same PR

[kanchansenlaskar]

I see you put arg name as "patch" unlike git apply where it has "patches". Does it not work with multiple patches/mboxes? Can you test once if not tested for the tools/library sake?

[adityagesh]

Interesting, I did not notice that.
Though the parameter is named patches, it accepts a Purepath and not list of Purepath.

I will verify the behavior and fix it along with Chi's comment below

[kanchansenlaskar]

By multiple I meant something like a pattern.
Ref:

lisa/lisa/transformers/kernel_source_installer.py

Line 75 in 5c8d025

file_pattern: str = "*.patch"

[adityagesh]

This is different, it is part of the modifier

[squirrelsc]

I just understood the scenario. Because the .mbx is always generated by b4, and the call sequence is always b4.am and git.apply. So the b4 can be called in git, or call git in b4, so it's easier to use.

[adityagesh]

How about something like this?

class Git(Tool):
  def apply_patch(self,....):
      # handles both apply and am
      
class B4(Tool):
  def am(self,....):
    self.run("am {patches}", ....)
    
  def apply(self,....):
      git = node.tool[Git]
      self.am()
      git.apply()

[squirrelsc]

1. The apply_patch and apply are confusing in the Git tool.
2. If call B4 in git, so the API can handle different types of patch files automatically. But if call git in B4, it still needs to know the type of patch files, and then call either git.apply or b4.apply.

[adityagesh]

The tool b4 has dependency on Git while pulling patches (taking Message_id as the parameter), so I don't think we can add b4 to Git.

Currently in Git.apply, it takes the path as parameter, which is basically the operation after we download the patch using b4.
B4 after downloading the patch should always call git apply to apply the patch.

The b4 apply that I showed above is : download patch using b4 -> apply downloaded patch using git

[squirrelsc]

1. I saw the code mark Git as a dependency. It's not necessary, because it's always used after Git tool is called.
2. The dependencies between b4 and git, are depended by how we manage them. The goal is to provide easy to use interface. If we provide B4 supports in git, the user doesn't need to take care the ext name, just call git to fit different file types. But if the B4 call git, it needs to know ext name firstly.

[adityagesh]

Are you recommending adding something like below in Git?

download_and_apply_patch(self, Message_Id):
 path = b4.am(Message_id)
 git.apply_patch(path)

I saw the code mark Git as a dependency. It's not necessary, because it's always used after Git tool is called.

If we have the tool B4, it is possible someone uses it directly before invoking git. b4 will fail is git is not installed and not set as a dependency

[squirrelsc]

It's like below. There is no conflict to block direct use b4.

    def apply(
        self,
        cwd: pathlib.PurePath,
        patches: pathlib.PurePath,
    ) -> None:
        file_extension = patches.suffix
        if file_extension == ".<b4's ext>"
            from .b4 import B4
            b4 = self.node.tools[B4]
            b4.am(...
            self.run(...
        else:
            self.run(...