[core] Add ROOT_LOG env var support for RLogger

[deveshbervar]

Why

Enables per-channel verbosity to be configured at startup via an
environment variable, without recompiling ROOT. This allows tracing
(e.g. CMS autoparsing after #7609) by simply setting ROOT_LOG.

What

Setting ROOT_LOG at startup now configures RLogger channel verbosity:

export ROOT_LOG='ROOT.InterpreterPerf=Debug(3),ROOT.RBrowser=Error'

Supported levels: Fatal, Error, Warning, Info, Debug, Debug(N).
gDebug is also applied as a global verbosity floor.

Changes

• RLogger.hxx: added fEnvVerbosity map to RLogManager, added
  GetEnvVerbosity(), updated GetEffectiveVerbosity() to check
  per-channel env overrides before falling back to global verbosity
• RLogger.cxx: constructor now parses ROOT_LOG and applies gDebug

Tests

Since RLogManager is a static singleton initialized once at process
startup, setenv() mid-test does not affect it. I would appreciate
guidance from the maintainer on the recommended approach for testing
this feature. Happy to add tests based on your feedback.

[deveshbervar]

@dpiparo ping! PR ready for review. I have implemented the ROOT_LOG
environment variable support as described in the issue. Please let me
know if any changes are needed, especially regarding the test approach
for the singleton RLogManager. Thank you!

[dpiparo]

Is testing perhaps still missing?

[deveshbervar]

Hi @dpiparo, tests have been added in core/foundation/test/RLoggerEnvVar.cxx.

Since RLogManager is a static singleton that parses ROOT_LOG once at
process startup, I used CMake's set_tests_properties ENVIRONMENT to
set ROOT_LOG before the test process starts, rather than setenv() mid-test.

Please let me know if this approach is acceptable or if you'd prefer
a different testing strategy. Thank you!

[pcanal]

Why are those code comments no longer relevant/helpful?

[deveshbervar]

Hi @pcanal,
Sorry, those comments were accidentally removed during editing.
Restored them now.

[deveshbervar]

Thank you @silverweed for the detailed review! I have addressed all the points:

• Restored the missing comment in RLogHandlerDefault
• Changed TrimWhitespace to use string_view to avoid copies
• Added Warning() calls for bad Debug(N) parsing and unrecognised levels
• Changed channelName and levelStr to string_view
• Added RLoggerEnvVar test to CMakeLists.txt

Regarding the roottest integration test suggestion - I would appreciate
guidance on the roottest structure if that is preferred over the current
unit test approach. Happy to add it.

[silverweed]

Thanks for the changes. Maybe a roottest integration test is not needed since ROOT_ADD_GTEST supports passing the environment...
Could you please add another test case where you explicitly set the verbosity and see that it takes precedence over the environment one?

[deveshbervar]

Hi @silverweed, I Added a test case that sets the channel verbosity explicitly to kInfo
while ROOT_LOG has it set to Error, and verifies the explicit setting
takes precedence. Thank you for the suggestion!

[github-actions]

Test Results

0 tests   0 ✅  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit 40d8a5f.

[silverweed]

@deveshbervar all CI builds failed in the configuration step: did you test your changes locally before updating the PR?

[deveshbervar]

Hi @silverweed, Sorry for not catching this before pushing.

Fixed the clang-format issues and string_view conversion errors.
Verified that the project builds successfully locally before pushing this update.