Tightening of position handlng

1) endPos works now even for NoPosition.
2) On the other hand, there's an assertion in Typer.typed which requires every non-empty tree that's type checked in a globally committable context to have a defined position.

Some fixes were needed to make the tests pass the new assert.

5 files changed, 15 insertions, 6 deletions

diff --git a/src/dotty/tools/dotc/core/TyperState.scala b/src/dotty/tools/dotc/core/TyperState.scala
index f46c58c90..455320ba8 100644
--- a/src/dotty/tools/dotc/core/TyperState.scala
+++ b/src/dotty/tools/dotc/core/TyperState.scala
@@ -41,6 +41,9 @@ class TyperState(val reporter: Reporter) extends DotClass with Showable {
   /** Is it allowed to commit this state? */
   def isCommittable: Boolean = false
 
+  /** Can this state be transitively committed until the top-level? */
+  def isGlobalCommittable: Boolean = false
+
   override def toText(printer: Printer): Text = "ImmutableTyperState"
 }
 
@@ -55,6 +58,10 @@ extends TyperState(reporter) {
   override def fresh(isCommittable: Boolean): TyperState =
     new MutableTyperState(this, new StoreReporter, isCommittable)
 
+  override val isGlobalCommittable =
+    isCommittable &&
+    (!previous.isInstanceOf[MutableTyperState] || previous.isGlobalCommittable)
+
   /** Commit typer state so that its information is copied into current typer state
    *  In addition (1) the owning state of undetermined or temporarily instantiated
    *  type variables changes from this typer state to the current one. (2) Variables
diff --git a/src/dotty/tools/dotc/typer/Applications.scala b/src/dotty/tools/dotc/typer/Applications.scala
index aa2227d63..2c1384524 100644
--- a/src/dotty/tools/dotc/typer/Applications.scala
+++ b/src/dotty/tools/dotc/typer/Applications.scala
@@ -562,7 +562,7 @@ trait Applications extends Compatibility { self: Typer =>
           ttree.tpe match {
             case alias: TypeRef if alias.symbol.isAliasType =>
               companionRef(alias) match {
-                case companion: TermRef => return untpd.ref(companion)
+                case companion: TermRef => return untpd.ref(companion) withPos tree.pos
                 case _ =>
               }
             case _ =>
diff --git a/src/dotty/tools/dotc/typer/Implicits.scala b/src/dotty/tools/dotc/typer/Implicits.scala
index 3878e5235..de74917a8 100644
--- a/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/src/dotty/tools/dotc/typer/Implicits.scala
@@ -245,7 +245,8 @@ trait Implicits { self: Typer =>
        !from.isError
     && !to.isError
     && (ctx.mode is Mode.ImplicitsEnabled)
-    && (inferView(dummyTreeOfType(from), to).isInstanceOf[SearchSuccess]))
+    && (inferView(dummyTreeOfType(from), to)(ctx.fresh.withExploreTyperState).isInstanceOf[SearchSuccess])
+    )
 
   /** Find an implicit conversion to apply to given tree `from` so that the
    *  result is compatible with type `to`.
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 85724b1ee..be84d1bea 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -492,7 +492,7 @@ class Typer extends Namer with Applications with Implicits {
   def typedIf(tree: untpd.If, pt: Type)(implicit ctx: Context) = track("typedIf") {
     val cond1 = typed(tree.cond, defn.BooleanType)
     val thenp1 = typed(tree.thenp, pt)
-    val elsep1 = typed(tree.elsep orElse untpd.unitLiteral, pt)
+    val elsep1 = typed(tree.elsep orElse untpd.unitLiteral withPos tree.pos, pt)
     cpy.If(tree, cond1, thenp1, elsep1).withType(thenp1.tpe | elsep1.tpe)
   }
 
@@ -952,6 +952,7 @@ class Typer extends Namer with Applications with Implicits {
   }
 
   def typed(tree: untpd.Tree, pt: Type = WildcardType)(implicit ctx: Context): Tree = ctx.traceIndented (s"typing ${tree.show}", show = true) {
+    if (!tree.isEmpty && ctx.typerState.isGlobalCommittable) assert(tree.pos.exists, tree)
     try adapt(typedUnadapted(tree, pt), pt)
     catch {
       case ex: CyclicReference => errorTree(tree, cyclicErrorMsg(ex))
diff --git a/src/dotty/tools/dotc/util/Positions.scala b/src/dotty/tools/dotc/util/Positions.scala
index 6dfb78c87..21ee788ca 100644
--- a/src/dotty/tools/dotc/util/Positions.scala
+++ b/src/dotty/tools/dotc/util/Positions.scala
@@ -78,13 +78,13 @@ object Positions {
       else this
 
     /** The zero-extent position with start and end at the point of this position */
-    def focus = Position(point)
+    def focus = if (exists) Position(point) else NoPosition
 
     /** The zero-extent position with start and end at the start of this position */
-    def startPos = Position(start)
+    def startPos = if (exists) Position(start) else NoPosition
 
     /** The zero-extent position with start and end at the end of this position */
-    def endPos = Position(end)
+    def endPos = if (exists) Position(end) else NoPosition
 
     /** A copy of this position with a different start */
     def withStart(start: Int) =