Merge pull request #1941 from sbt/wip/1940

Wip/1940

main/command/src/main/scala/sbt/BasicCommands.scala

@@ -13,6 +13,8 @@ import BasicKeys._
 
 import java.io.File
 
+import scala.util.control.NonFatal
+
 object BasicCommands {
   lazy val allBasicCommands = Seq(nop, ignore, help, completionsCommand, multi, ifLast, append, setOnFailure, clearOnFailure, stashOnFailure, popOnFailure, reboot, call, early, exit, continuous, history, shell, read, alias) ++ compatCommands
 
@@ -27,7 +29,10 @@ object BasicCommands {
 
   def helpParser(s: State) =
     {
-      val h = (Help.empty /: s.definedCommands)(_ ++ _.help(s))
+      val h = (Help.empty /: s.definedCommands) { (a, b) =>
+        a ++
+          (try b.help(s) catch { case NonFatal(ex) => Help.empty })
+      }
       val helpCommands = h.detail.keySet
       val spacedArg = singleArgument(helpCommands).?
       applyEffect(spacedArg)(runHelp(s, h))
@@ -35,7 +40,12 @@ object BasicCommands {
 
   def runHelp(s: State, h: Help)(arg: Option[String]): State =
     {
-      val message = Help.message(h, arg)
+      val message = try
+        Help.message(h, arg)
+      catch {
+        case NonFatal(ex) =>
+          ex.toString
+      }
       System.out.println(message)
       s
     }

notes/0.13.9/help.markdown

@@ -0,0 +1,16 @@
+  [@cunei]: https://github.com/cunei
+  [@eed3si9n]: https://github.com/eed3si9n
+  [@gkossakowski]: https://github.com/gkossakowski
+  [@jsuereth]: https://github.com/jsuereth
+  [@DavidPerezIngeniero]: https://github.com/DavidPerezIngeniero
+
+  [1900]: https://github.com/sbt/sbt/issues/1900
+  [1940]: https://github.com/sbt/sbt/pull/1940
+
+### Changes with compatibility implications
+
+### Improvements
+
+### Fixes
+
+- Captures errors on `help` command. [#1900][1900]/[#1940][1940] by [@DavidPerezIngeniero][@DavidPerezIngeniero]