Make import suggestions timeout configurable

We now expose it as a var, which can be set by IDEs or other tools.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -487,16 +487,13 @@ trait ImplicitRunInfo:
    */
   private inline val suggestFirstImplicitsTimeOut = 10000
 
-  private var importSuggestionBudget: Long = suggestFirstImplicitsTimeOut
-
-  /** The current timeout for import suggestions */
-  def nextImportSuggestionTimeout() = importSuggestionBudget
-
-  /** Reduce the import suggestion timeout by `ms`, but make sure that
-   *  the new timeout is at least half the old one.
+  /** Global default timeout to stop looking for further implicit suggestions, in ms.
+   *  This is usually for the first import suggestion; subsequent suggestions
+   *  may get smaller timeouts. Specifically, the importSuggestions method reduces
+   *  the budget available after it is run by the time it took, but never less
+   *  than to half of the previous budget.
    */
-  def reduceImportSuggestionTimeout(ms: Long) =
-    importSuggestionBudget = (importSuggestionBudget - ms) max (importSuggestionBudget / 2)
+  var importSuggestionBudget: Long = 10000
 
   private def isExcluded(sym: Symbol) =
     if migrateTo3 then false else sym.is(Package) || sym.isPackageObject

compiler/src/dotty/tools/dotc/typer/ImportSuggestions.scala

@@ -142,7 +142,7 @@ trait ImportSuggestions:
    */
   private def importSuggestions(pt: Type)(using Context): (List[TermRef], List[TermRef]) =
     val timer = new Timer()
-    val allotted = ctx.run.nextImportSuggestionTimeout()
+    val allotted = ctx.run.importSuggestionBudget
     if allotted <= 1 then return (Nil, Nil)
     implicits.println(i"looking for import suggestions, timeout = ${allotted}ms")
     val start = System.currentTimeMillis()
@@ -252,7 +252,9 @@ trait ImportSuggestions:
         (Nil, Nil)
     finally
       timer.cancel()
-      ctx.run.reduceImportSuggestionTimeout(System.currentTimeMillis() - start)
+      ctx.run.importSuggestionBudget =
+        (ctx.run.importSuggestionBudget - (System.currentTimeMillis() - start))
+        `max` (ctx.run.importSuggestionBudget / 2)
   end importSuggestions
 
   /** The `ref` parts of this list of pairs, discarding subsequent elements that