Support relative path in explicit ErrorLog value

[pavel-mikula-sonarsource]

Description

#1015 fixed an issue that the explicit ErrorLog property provided by a user wasn't handled properly. Since 5.3.0 we do accept user-provided values.

Problem is that we only support absolute paths now because ErrorLog could be relative to the project directory. Such value gets propagated to the ProjectInfo.xml as a relative path but they don't share the same base when processing.

Originally reported on community forum

Reproducer

To reproduce the issue, add relative ErrorLog property to a project file:

<ErrorLog>obj\issues.json</ErrorLog>

Then end step will produce a warning:

WARN: No Roslyn issue reports were found. The C# files have not been analyzed. You can get help on the community forum: https://community.sonarsource.com

Workaround

To workaround the issue, you can set absolute path in the ErrorLog property:

<ErrorLog>$(MSBuildProjectDirectory)\obj\issues.json</ErrorLog>

[pavel-mikula-sonarsource]

The same issue affects the Razor property as well.

[andrei-epure-sonarsource]

should this be supported in the S4NET or rather in the SQ plugin @pavel-mikula-sonarsource ?

[pavel-mikula-sonarsource]

This should be fixed on S4NET side as the target file also contains the ultimate source of truth about the base path that the ErrorLog is relative to.