[PATCH 3 of 3] extensions: add unwrapfunction to undo wrapfunction

[Martijn Pieters]

On 1 July 2016 at 13:09, Jun Wu <quark at fb.com> wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1467374153 -3600
> #      Fri Jul 01 12:55:53 2016 +0100
> # Node ID 7a68b01000d12e1795d142cdb32fdd62a5ffc8cb
> # Parent  de798903374922317eb2cbca9733ba0cea415780
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r 7a68b01000d1
> extensions: add unwrapfunction to undo wrapfunction
>
> Before this patch, we don't have a safe way to undo a wrapfunction because
> other extensions may wrap the same function and calling setattr will undo
> them accidentally.
>
> This patch adds an "unwrapfunction" to address the issue. It removes the
> wrapper from the wrapper chain, and re-wraps everything, which is not the
> most efficient but short and easy to understand. We can revisit the code
> if we have perf issues with long chains.
>
> The "undo" feature is useful in cases like wrapping a function just in
> a scope. And it allows extensions running with chg to add and remove their
> wrappers dynamically in reposetup without starting a new chgserver.
>
> diff --git a/mercurial/extensions.py b/mercurial/extensions.py
> --- a/mercurial/extensions.py
> +++ b/mercurial/extensions.py
> @@ -303,6 +303,19 @@ def wrapfunction(container, funcname, wr
>      setattr(container, funcname, wrap)
>      return origfn
>
> +def unwrapfunction(container, funcname, wrapper):
> +    '''Undo wrapfunction
> +
> +    Pass the same arguments with wrapfunction to undo a wrap.
> +    Handles stacked wrappers correctly.
> +    '''
> +    chain = getwrapperchain(container, funcname)
> +    origfn = chain.pop()
> +    chain.remove(wrapper)
> +    setattr(container, funcname, origfn)
> +    for wrapper in reversed(chain):
> +        wrapfunction(container, funcname, wrapper)
> +


You could just use a stack of functions to rewrap; this avoids having
to re-do the whole chain:

    chain = getwrapperchain(container, funcname)[::-1]
    rewrap = []
    while chain:
        wrapper = chain.pop()
        if wrapper == origfn:
            break
        rewrap.append(wrapper)
    if chain:
        # we found the original and removed it; rewrap whatever we had to remove
                 # to find it.
        setattr(container, funcname, chain[-1])
        while rewrap:
            wrapfunction(container, funcname, rewrap.pop())

>  def getwrapperchain(container, funcname):
>      '''get a chain of wrappers of a function
>
> diff --git a/tests/test-extensions-wrapfunction.py b/tests/test-extensions-wrapfunction.py
> new file mode 100644
> --- /dev/null
> +++ b/tests/test-extensions-wrapfunction.py
> @@ -0,0 +1,24 @@
> +from __future__ import absolute_import, print_function
> +
> +from mercurial import extensions
> +
> +def genwrap(x):
> +    def f(orig, *args, **kwds):
> +        return [x] + orig(*args, **kwds)
> +    return f
> +
> +wrappers = [genwrap(i) for i in range(5)]
> +
> +class dummyclass(object):
> +    def foo(self):
> +        return ['orig']
> +
> +dummy = dummyclass()
> +
> +for w in wrappers + [wrappers[0]]:
> +    extensions.wrapfunction(dummy, 'foo', w)
> +    print(dummy.foo())
> +
> +for i in [3, 0, 4, 0, 2, 1]:
> +    extensions.unwrapfunction(dummy, 'foo', wrappers[i])
> +    print(dummy.foo())
> diff --git a/tests/test-extensions-wrapfunction.py.out b/tests/test-extensions-wrapfunction.py.out
> new file mode 100644
> --- /dev/null
> +++ b/tests/test-extensions-wrapfunction.py.out
> @@ -0,0 +1,12 @@
> +[0, 'orig']
> +[1, 0, 'orig']
> +[2, 1, 0, 'orig']
> +[3, 2, 1, 0, 'orig']
> +[4, 3, 2, 1, 0, 'orig']
> +[0, 4, 3, 2, 1, 0, 'orig']
> +[0, 4, 2, 1, 0, 'orig']
> +[4, 2, 1, 0, 'orig']
> +[2, 1, 0, 'orig']
> +[2, 1, 'orig']
> +[1, 'orig']
> +['orig']
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-- 
Martijn Pieters