add support for parallel builds (#240)

README.md

@@ -210,6 +210,25 @@ import org.scoverage.coveralls.TravisPro
 coverallsService := Some(TravisPro)
 ```
 
+## Uploading coverage from parallel CI builds
+
+[Coveralls supports merging reports from multiple CI builds.](https://docs.coveralls.io/parallel-build-webhook)
+Each report must be flagged as coming from a parallel job, then a webhook must be called after all jobs have completed to merge the reports together.
+
+To mark uploaded reports as parallel, either:
+
+### Put the flag directly in `build.sbt`
+```scala
+import org.scoverage.coveralls.Imports.CoverallsKeys._
+
+coverallsParallel := true
+```
+
+### Set an environment variable
+```shell
+export COVERALLS_PARALLEL=true
+```
+
 # License
 
 `sbt-coveralls` is open source software released under the [Apache 2

src/main/scala/org/scoverage/coveralls/CoverallPayloadWriter.scala

@@ -12,6 +12,7 @@ class CoverallPayloadWriter(
     coverallsFile: File,
     repoToken: Option[String],
     service: Option[CIService],
+    parallel: Boolean,
     gitClient: GitClient
 )(implicit log: Logger) {
   import gitClient._
@@ -38,6 +39,10 @@ class CoverallPayloadWriter(
     // to provide an unique additional label in jobs with multiple submissions
     writeOpt("flag_name", sys.env.get("COVERALLS_FLAG_NAME"))
 
+    if (parallel) {
+      gen.writeBooleanField("parallel", true)
+    }
+
     addGitInfo()
 
     gen.writeFieldName("source_files")

src/main/scala/org/scoverage/coveralls/CoverallsPlugin.scala

@@ -28,6 +28,7 @@ object Imports {
     val coverallsEndpoint = SettingKey[Option[String]]("coverallsEndpoint")
     val coverallsGitRepoLocation =
       SettingKey[Option[String]]("coveralls-git-repo")
+    val coverallsParallel = SettingKey[Boolean]("coverallsParallel")
   }
 }
 
@@ -56,7 +57,8 @@ object CoverallsPlugin extends AutoPlugin {
     },
     coverallsFile := crossTarget.value / "coveralls.json",
     coberturaFile := crossTarget.value / "coverage-report" / "cobertura.xml",
-    coverallsGitRepoLocation := Some(".")
+    coverallsGitRepoLocation := Some("."),
+    coverallsParallel := sys.env.get("COVERALLS_PARALLEL").contains("true")
   )
 
   val aggregateFilter = ScopeFilter(
@@ -98,6 +100,7 @@ object CoverallsPlugin extends AutoPlugin {
       coverallsFile.value,
       repoToken,
       coverallsService.value,
+      coverallsParallel.value,
       new GitClient(repoRootDirectory)
     )
 

src/test/scala/org/scoverage/coveralls/CoverallPayloadWriterTest.scala

@@ -32,13 +32,15 @@ class CoverallPayloadWriterTest
   def coverallsWriter(
       writer: Writer,
       tokenIn: Option[String],
-      service: Option[CIService]
+      service: Option[CIService],
+      parallel: Boolean,
   ): (CoverallPayloadWriter, Writer) = {
     val payloadWriter = new CoverallPayloadWriter(
       new File(".").getAbsoluteFile,
       new File("."),
       tokenIn,
       service,
+      parallel,
       testGitClient
     ) {
       override def generator(file: File) = {
@@ -66,7 +68,8 @@ class CoverallPayloadWriterTest
         val (payloadWriter, writer) = coverallsWriter(
           new StringWriter(),
           Some("testRepoToken"),
-          Some(testService)
+          Some(testService),
+          false
         )
 
         payloadWriter.start
@@ -81,7 +84,7 @@ class CoverallPayloadWriterTest
 
       "generate a correct starting payload without a CI service" in {
         val (payloadWriter, writer) =
-          coverallsWriter(new StringWriter(), Some("testRepoToken"), None)
+          coverallsWriter(new StringWriter(), Some("testRepoToken"), None, false)
 
         payloadWriter.start
         payloadWriter.flush()
@@ -109,7 +112,8 @@ class CoverallPayloadWriterTest
         val (payloadWriter, writer) = coverallsWriter(
           new StringWriter(),
           Some("testRepoToken"),
-          Some(TravisCI)
+          Some(TravisCI),
+          false
         )
         payloadWriter.addSourceFile(
           SourceFileReport(
@@ -128,14 +132,28 @@ class CoverallPayloadWriterTest
         val (payloadWriter, writer) = coverallsWriter(
           new StringWriter(),
           Some("testRepoToken"),
-          Some(TravisCI)
+          Some(TravisCI),
+          false
         )
 
         payloadWriter.start
         payloadWriter.end()
 
         writer.toString should endWith("]}")
       }
+
+      "include parallel correctly" in {
+        val (payloadWriter, writer) = coverallsWriter(new StringWriter(), Some("testRepoToken"), None, true)
+
+        payloadWriter.start
+        payloadWriter.flush()
+
+        writer.toString should equal(
+          """{"repo_token":"testRepoToken","parallel":true,""" +
+            expectedGit +
+            ""","source_files":["""
+        )
+      }
     }
   }
 }