Fix typos

Author: Blaisorblade

src/dotty/tools/dotc/ast/Trees.scala

@@ -48,7 +48,7 @@ object Trees {
    *     the existing tree transparently, assigning its `tpe` field,
    *     provided it was `null` before.
    *   - It is impossible to embed untyped trees in typed ones.
-   *   - Typed trees can be embedded untyped ones provided they are rooted
+   *   - Typed trees can be embedded in untyped ones provided they are rooted
    *     in a TypedSplice node.
    *   - Type checking an untyped tree should remove all embedded `TypedSplice`
    *     nodes.
@@ -855,7 +855,7 @@ object Trees {
 
     val cpy: TreeCopier
 
-    /** A class for copying trees. The copy methods avid creating a new tree
+    /** A class for copying trees. The copy methods avoid creating a new tree
      *  If all arguments stay the same.
      *
      * Note: Some of the copy methods take a context.

src/dotty/tools/dotc/transform/TreeTransform.scala

@@ -42,7 +42,7 @@ object TreeTransforms {
    *            the general dispatch overhead as opposed to the concrete work done in transformations. So that leaves us with
    *            0.2sec, or roughly 600M processor cycles.
    *
-   *            Now, to the amount of work that needs to be done. The codebase produces of about 250'000 trees after typechecking.
+   *            Now, to the amount of work that needs to be done. The codebase produces an average of about 250'000 trees after typechecking.
    *            Transformations are likely to make this bigger so let's assume 300K trees on average. We estimate to have about 100
    *            micro-transformations. Let's say 5 transformation groups of 20 micro-transformations each. (by comparison,
    *            scalac has in excess of 20 phases, and most phases do multiple transformations). There are then 30M visits
@@ -208,7 +208,7 @@ object TreeTransforms {
       if (cls.getDeclaredMethods.exists(_.getName == name)) cls != classOf[TreeTransform]
       else hasRedefinedMethod(cls.getSuperclass, name)
 
-    /** Create an index array `next` of size one larger than teh size of `transforms` such that
+    /** Create an index array `next` of size one larger than the size of `transforms` such that
      *  for each index i, `next(i)` is the smallest index j such that
      *
      *  i <= j