Multi-file import

[joka921]

So far, QLever read its input from a single file or from standard input. This made it hard to associate graph information per file. It also caused problems when parallel parsing was activated and a Turtle file did not have all its prefix declarations at the beginning. With this change, QLever can read its input from multiple input streams (files or pipes), and the streams are parsed concurrently. It can be specified separately for each stream which default graph to use for that stream and whether to use the parallel parser or not. Specifying a value for "parallel-parsing" in the .settings.json file is now deprecated.

There will a corresponding change in https://github.com/ad-freiburg/qlever-control next that enables the convenient control of this new functionality from a Qleverfile.

[codecov]

Codecov Report

Attention: Patch coverage is 97.19626% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.47%. Comparing base (77ea2c6) to head (d14cd8e).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
src/parser/RdfParser.cpp	96.72%	1 Missing and 1 partial ⚠️
src/index/IndexImpl.cpp	96.29%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1537      +/-   ##
==========================================
+ Coverage   88.22%   88.47%   +0.24%     
==========================================
  Files         360      363       +3     
  Lines       27095    27533     +438     
  Branches     3647     3714      +67     
==========================================
+ Hits        23905    24360     +455     
+ Misses       1953     1941      -12     
+ Partials     1237     1232       -5     

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[hannahbast]

1-1 with Johannes, committed some minor changes, looks very good now and we tested it end-to-end

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=d14cd8e18b63e615615342a76da33499ef5babcc&prev=a9a9ae46e72a7e9d2a2a09d691a10e64d62b3952

[sonarcloud]

Quality Gate passed

Issues
4 New issues
1 Accepted issue

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud