Avoid repeated unnecessary logging in traceIndented

smarter · smarter · commit fdb3540007dd · 2015-11-24T21:32:50.000+01:00
While trying to debug #943 I noticed that the exception output from traceIndented was interspersed with unrelated logging output, this happened because `question` in traceIndented is by-value and was evaluated both before executing an operation and afterwards.
diff --git a/src/dotty/tools/dotc/reporting/Reporter.scala b/src/dotty/tools/dotc/reporting/Reporter.scala
@@ -152,7 +152,12 @@ trait Reporting { this: Context =>
       case _ => String.valueOf(res)
     }
     if (printer eq config.Printers.noPrinter) op
-    else traceIndented[T](s"==> $question?", (res: Any) => s"<== $question = ${resStr(res)}")(op)
+    else {
+      // Avoid evaluating question multiple time, since each evaluation
+      // may cause some extra logging output.
+      val q: String = question
+      traceIndented[T](s"==> $q?", (res: Any) => s"<== $q = ${resStr(res)}")(op)
+    }
   }
 
   def traceIndented[T](leading: => String, trailing: Any => String)(op: => T): T =

Original file line number	Diff line number	Diff line change
`@@ -152,7 +152,12 @@ trait Reporting { this: Context =>`
`152`	`152`	`case _ => String.valueOf(res)`
`153`	`153`	`}`
`154`	`154`	`if (printer eq config.Printers.noPrinter) op`
`155`		`- else traceIndented[T](s"==> $question?", (res: Any) => s"<== $question = ${resStr(res)}")(op)`
	`155`	`+ else {`
	`156`	`+ // Avoid evaluating question multiple time, since each evaluation`
	`157`	`+ // may cause some extra logging output.`
	`158`	`+ val q: String = question`
	`159`	`+ traceIndented[T](s"==> $q?", (res: Any) => s"<== $q = ${resStr(res)}")(op)`
	`160`	`+ }`
`156`	`161`	`}`
`157`	`162`
`158`	`163`	`def traceIndented[T](leading: => String, trailing: Any => String)(op: => T): T =`