Add build-level keys to the tab completion

Fixes #2460
Fixes #2851
Ref #2707, #2708, #2469

Unlike the previous attempts at fixing the handling of build-level
keys, this change does not change the main parsing logic, which uses
`getKey` to retrieve the key from the key map.
The fact that shell worked pre-0.13.11 means that the parsing was ok.

What this changes is just the "example" keys supplied to the parser so
the tab completion works.

main/src/main/scala/sbt/internal/Act.scala

@@ -134,7 +134,16 @@ object Act {
         token(ID !!! "Expected key" examples dropHyphenated(keys)) flatMap { keyString =>
           getKey(keyMap, keyString, idFun)
         }
-      keyParser(index.keys(proj, conf, task))
+      // Fixes sbt/sbt#2460 and sbt/sbt#2851
+      // The parser already accepts build-level keys.
+      // This queries the key index so tab completion will list the build-level keys.
+      val buildKeys: Set[String] =
+        proj match {
+          case Some(ProjectRef(uri, id)) => index.keys(Some(BuildRef(uri)), conf, task)
+          case _                         => Set()
+        }
+      val keys: Set[String] = index.keys(proj, conf, task) ++ buildKeys
+      keyParser(keys)
     }
 
   def getKey[T](keyMap: Map[String, AttributeKey[_]], keyString: String, f: AttributeKey[_] => T): Parser[T] =

notes/0.13.14/buildlevelkey.md

@@ -0,0 +1,9 @@
+### Bug fixes
+
+- Fixes regressions in sbt 0.13.11 - 0.13.13 that processed build-level keys incorrectly. [#2851][2851]/[#2460][2460] by [@eed3si9n]
+
+  [#2851]: https://github.com/sbt/sbt/issues/2851
+  [#2460]: https://github.com/sbt/sbt/issues/2460
+  [@eed3si9n]: https://github.com/eed3si9n
+  [@dwijnand]: https://github.com/dwijnand
+  [@Duhemm]: https://github.com/Duhemm

sbt/src/sbt-test/actions/completions/build.sbt

@@ -0,0 +1,29 @@
+import complete.{ Completion, Completions, DefaultParsers, Parser }
+import DefaultParsers._
+import Command.applyEffect
+import CommandUtil._
+
+lazy val root = (project in file(".")).
+  enablePlugins(FooPlugin).
+  settings(
+    commands += checkCompletionsCommand
+  )
+
+// This checks the tab completion lists build-level keys
+def checkCompletionsCommand = Command.make("checkCompletions")(completionsParser)
+def completionsParser(state: State) =
+  {
+    val notQuoted = (NotQuoted ~ any.*) map { case (nq, s) => (nq +: s).mkString }
+    val quotedOrUnquotedSingleArgument = Space ~> (StringVerbatim | StringEscapable | notQuoted)
+    applyEffect(token(quotedOrUnquotedSingleArgument ?? "" examples ("", " ")))(runCompletions(state))
+  }
+def runCompletions(state: State)(input: String): State = {
+  val xs = Parser.completions(state.combinedParser, input, 9).get map {
+    c => if (c.isEmpty) input else input + c.append
+  } map { c =>
+    c.replaceAll("\n", " ")
+  }
+  println(xs)
+  assert(xs == Set("myTask"))
+  state
+}

sbt/src/sbt-test/actions/completions/project/FooPlugin.scala

@@ -0,0 +1,15 @@
+import sbt._
+import syntax._
+
+object FooPlugin extends AutoPlugin {
+  override def trigger = noTrigger
+  object autoImport {
+    val myTask = taskKey[Unit]("My task")
+  }
+
+  import autoImport._
+
+  override def buildSettings = super.buildSettings ++ Seq(
+    myTask := println("Called my task")
+  )
+}

sbt/src/sbt-test/actions/completions/test

@@ -0,0 +1 @@
+> checkCompletions my