cmake plugin: use build snaps to search paths

[sergiusens]

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on bug reports?
• If this is a new feature. Have you discussed the design on the forum?
• Have you successfully run ./runtests.sh static?
• Have you successfully run ./runtests.sh tests/unit?

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[hsitter]

lgtm 👍

(builds on 2397; this PR on top is horrible to read 🤢 )

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@305304e). Click here to learn what that means.
The diff coverage is 96.29%.

@@            Coverage Diff            @@
##             master    #2399   +/-   ##
=========================================
  Coverage          ?   90.09%           
=========================================
  Files             ?      196           
  Lines             ?    12885           
  Branches          ?     1955           
=========================================
  Hits              ?    11609           
  Misses            ?      876           
  Partials          ?      400

Impacted Files	Coverage Δ
snapcraft/plugins/cmake.py	87.69% <96.29%> (ø)

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[hsitter]

@sergiusens At the time we couldn't think of a way to write the conditional in a more straight forward way. I've since put a stop-gap in place in our tooling, where I ended up writing it like this (untested python translation):

configflags = self.options.configflags[:]
for flag in self.options.configflags:
    parts = flag.split('=', 2)
    if parts[0] != "-DCMAKE_FIND_ROOT_PATH":
        continue

    configflags.remove(flag)
    build_snap_paths.append(parts[1])

if build_snap_paths:
	configflags.append("-DCMAKE_FIND_ROOT_PATH={}".format(";".join(build_snap_paths)))

i.e. instead of handling the append as a condition I've turned it it into a cleanup problem. the loop now pulls the original flag out of the list to "clean it up" and push its value into the path list so it gets joined along with all the other values.

[sergiusens]

I chose a different approach, thanks for the nudge 😄

[hsitter]

Looks better than before 👍