Set stacktrace.abs_path

[felixbarny]

To make the integration with the Code app easier, they need the abs_path of the stack frame. In Java it's impossible to determine the exact path within the root of the git repository, like apm-agent-core/src/main/java/co/elastic/apm/agent/report/serialize/DslJsonSerializer.java but based on the package name and file name, we can get something like co/elastic/apm/agent/report/serialize/DslJsonSerializer.java.

The question is if it's ok to put a relative path in abs_path.

Checklist

• Implement code
• Add tests
• Update documentation
• Update CHANGELOG.md
• Update supported-technologies.asciidoc
• Added an API method or config option? Document in which version this will be introduced.

[codecov-io]

Codecov Report

Merging #856 into master will increase coverage by 0.6%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #856     +/-   ##
===========================================
+ Coverage     64.22%   64.83%   +0.6%     
  Complexity       84       84             
===========================================
  Files           230      230             
  Lines          9329     9449    +120     
  Branches       1214     1245     +31     
===========================================
+ Hits           5992     6126    +134     
+ Misses         2956     2945     -11     
+ Partials        381      378      -3

Impacted Files	Coverage Δ	Complexity Δ
.../apm/agent/report/serialize/DslJsonSerializer.java	89.71% <0%> (+3.62%)	0% <0%> (ø)	⬇️

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[eyalkoren]

This allocates two String objects (substring() and replace()) for each stack frame of each span. Can we use a char-copy to a StringBuilder that includes the char replacement as well?
If so, can it also be used for handling inner classes, lambdas and the like or that using getFileName() will always be safer?

[felixbarny]

We decided in today's meeting that it's not a good idea to put a relative path in a field called abs_path. For now, the code search integration should rely on just the file name, even if it may cause ambiguities.

We discovered discrepancies between the agent implementations as some put a relative path in the filename and some only put the base path in there.

Going forward, we should investigate alignment with ECS for stack traces. There are discussions going on at elastic/ecs#154 and elastic/ecs#563.