Fix benchmarks not running on Linux

Apparently, "swift test" has different behavior on Linux:
1. It outputs to stdout instead of stderr
2. Format of output itself differs, so regex in ppbenchmarks has to be adjusted.

Author: tsolomko

.travis.yml

@@ -23,14 +23,16 @@ jobs:
       os: osx
       osx_image: xcode10
       script:
+      # On macOS swift test (i.e. XCTest) outputs to stderr so we need to redirect pipes.
       - swift test -c release -Xswiftc -enable-testing --filter BitByteDataBenchmarks 2>&1 | ./ppbenchmarks.py 
     - language: generic
       os: linux
       dist: trusty
       install:
       - eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"
       script:
-      - swift test -c release -Xswiftc -enable-testing --filter BitByteDataBenchmarks 2>&1 | ./ppbenchmarks.py 
+      # On Linux swift test outputs to stdout so we don't need to do anything.
+      - swift test -c release -Xswiftc -enable-testing --filter BitByteDataBenchmarks | ./ppbenchmarks.py 
     - stage: deploy
       if: tag IS present
       language: generic

ppbenchmarks.py

@@ -8,7 +8,15 @@
 for line in sys.stdin:
     line = line.rstrip()
     print(line)
-    p = re.compile("Test Case '-\[BitByteDataBenchmarks\.(.+Benchmarks) (test.+)\]'.+average: (\d+.\d+), relative standard deviation: (\d+.\d+)\%")
+    p = None
+    # Output format of 'swift test' differs between macOS and Linux platforms.
+    if sys.platform == "darwin":
+        p = re.compile("Test Case '-\[BitByteDataBenchmarks\.(.+Benchmarks) (test.+)\]'.+average: (\d+.\d+), relative standard deviation: (\d+.\d+)\%")
+    elif sys.platform == "linux":
+        p = re.compile("Test Case '(.+Benchmarks)\.(test.+)'.+average: (\d+.\d+), relative standard deviation: (\d+.\d+)\%")
+    else:
+        raise Exception("Unknown platform: " + sys.platform) 
+    
     matches = p.findall(line)
     if len(matches) == 1 and len(matches[0]) == 4:
         benchmark_name = matches[0][0]