Fix opentelemetry-proto file exists check

[eguzki]

Fixes #1823

Changes

Fix CMake EXISTS syntax

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: eguzki / name: Eguzki Astiz Lezaun (4c1611e, cd12159)

[marcalff]

Thanks for the fix.

The original bug is mine, sorry I must have been distracted when doing last minute changes.

[codecov]

Codecov Report

Merging #1824 (cd12159) into main (7e26a7e) will not change coverage.
The diff coverage is n/a.

❗ Current head cd12159 differs from pull request most recent head 9c29437. Consider uploading reports for the commit 9c29437 to get more accurate results

Additional details and impacted files

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##             main    #1824   +/-   ##
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  Coverage   85.73%   85.73%           
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  Files         171      171           
  Lines        5240     5240           
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  Hits         4492     4492           
  Misses        748      748           

[ThomsonTan]

@marcalff , do you think we can have a test on this passed in env var?

[marcalff]

Tested locally with:

malff@localhost.localdomain:build-opentelemetry-cpp> pwd
/home/malff/CODE/MY_GITHUB/build-opentelemetry-cpp

ccmake \
-DOTELCPP_PROTO_PATH=/home/malff/CODE/MY_GITHUB/opentelemetry-proto \
-DWITH_OTLP=ON \
-DWITH_OTLP_HTTP=ON \
-DWITH_OTLP_GRPC=ON \
 ../opentelemetry-cpp \

CMake result without the fix:

 CMake Error at cmake/opentelemetry-proto.cmake:30 (message):
   OTELCPP_PROTO_PATH does not point to a opentelemetry-proto repository

CMake result with the fix:

 opentelemetry-proto dependency satisfied by: external path

So the fix is working.

OTELCPP_PROTO_PATH also shows in the ccmake UI.

@ThomsonTan
Using environment variables will be odd, may be I don't understand what you suggest.

[lalitb]

@ThomsonTan - Hope this is ok to merge. If there are any specific test scenarios, we can address them separately.