Update docs

Author: odersky

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

@@ -617,38 +617,37 @@ trait ImplicitRunInfo:
 
   /** The implicit scope of a type `tp`, which is specified by the following definitions.
    *
-   *  A reference is an _anchor_ if it refers to a class or an abstract type or an
-   *  opaque type alias. References to object classes are also anchors, except that
-   *  references to packages and package objects are anchors only under -source:3.0-migration.
+   *  A reference is an _anchor_ if it refers to an object, a class, a trait, an
+   *  abstract type, or an opaque type alias. References to packages and package
+   *  objects are anchors only under -source:3.0-migration.
    *
-   *  The _parts_ of a type `T` is a set of type references defined as follows:
+   *  The _anchors_ of a type `T` is a set of references defined as follows:
    *
-   *   - If `T` is an alias of `T'`, the parts of `T'`.
-   *   - If `T` is a type reference to an anchor, `T` itself and the prefix parts of `T`.
-   *   - If `T` is a reference to a type parameter, the parts of its bounds.
-   *   - If `T` is a term reference, the parts of its underlying type, and the prefix parts of `T`.
-   *   - If `T` is the this-type of a static object, the parts of the term reference to that object.
-   *   - If `T` is a constant type, the parts of its underlying type.
-   *   - If `T` is some other type, the union of parts of each constituent type of `T`
-   *     that is of one of the forms above.
-   *
-   *  The _prefix parts_ of a type reference or term reference `P#A` with prefix `P` is
-   *  a set of type references defined as follows:
-   *
-   *   - If `P` is a term reference `(Q # x).type, the prefix parts of `Q`.
-   *     Under -source:3.0-migration, also include the parts of `P`'s underlying type.
-   *   - If `P` is some other singleton type, the empty set.
-   *   - If `P` is some other type, the parts of `P`.
+   *   - If `T` is a reference to an anchor, `T` itself plus, if `T` is of the form
+   *     `P#A`, the anchors of `P`.
+   *   - If `T` is an alias of `U`, the anchors of `U`.
+   *   - If `T` is a reference to a type parameter, the union of the anchors of both of its bounds.
+   *   - If `T` is a singleton reference, the anchors of its underlying type, plus,
+   *     if `T` is of the form `(P#x).type`, the anchors of `P`.
+   *   - If `T` is the this-type of a static object, the anchors of a term reference to that object.
+   *   - If `T` is some other type, the union of the anchors of each constituent type of `T`.
    *
    *  The _implicit scope_ of a type `tp` is the smallest set S of term references (i.e. TermRefs)
    *  such that
    *
    *   - If `T` is a reference to a class, S includes a reference to the companion object
    *     of the class, if it exists, as well as the implicit scopes of all of `T`'s parent classes.
-   *   - If `T` is a reference to an opaque type alias or abstract type named `A`, S includes
+   *   - If `T` is a reference to an object, S includes `T` itself as well as
+   *     the implicit scopes of all of `T`'s parent classes.
+   *   - If `T` is a reference to an opaque type alias named `A`, S includes
    *     a reference to an object `A` defined in the same scope as the type, if it exists,
    *     as well as the implicit scope of `T`'s underlying type or bounds.
-   *   - If `T` is some other type, S includes the implicit scopes of all parts of `T`.
+   *   - If `T` is a reference to an an abstract type named `A`, S includes
+   *     a reference to an object `A` defined in the same scope as the type, if it exists,
+   *     as well as the implicit scopes of `T`'s lower and upper bound.
+   *   - If `T` is a reference to an anchor of the form `p.A` then S also includes
+   *     all term references on the path `p`.
+   *   - If `T` is some other type, S includes the implicit scopes of all anchors of `T`.
    */
   def implicitScope(tp: Type)(using Context): OfTypeImplicits =
     object liftToAnchors extends TypeMap:

docs/docs/reference/changed-features/implicit-resolution.md

@@ -52,6 +52,39 @@ Both `a` and `b` are visible as implicits at the point of the definition
 of `type C`. However, a reference to `p.o.C` outside of package `p` will
 have only `b` in its implicit search scope but not `a`.
 
+In more detail, here are the rules for what constitutes the implicit scope of
+a type:
+
+**Definition:** A reference is an _anchor_ if it refers to an object, a class, a trait, an abstract type, or an opaque type alias. References to packages and package objects are anchors only under -source:3.0-migration.
+
+**Definition:** The _anchors_ of a type _T_ is a set of references defined as follows:
+
+  - If _T_ is a reference to an anchor, _T_ itself plus, if _T_ is of the form _P#A_, the anchors of _P_.
+  - If _T_ is an alias of _U_, the anchors of _U_.
+  - If _T_ is a reference to a type parameter, the union of the anchors of both of its bounds.
+  - If _T_ is a singleton reference, the anchors of its underlying type, plus,
+    if _T_ is of the form _(P#x).type_, the anchors of _P_.
+  - If _T_ is the this-type _o.this_ of a static object _o_, the anchors of a term reference _o.type_ to that object.
+  - If _T_ is some other type, the union of the anchors of each constituent type of _T_.
+
+ **Definition:** The _implicit scope_ of a type _T_ is the smallest set _S_ of term references such that
+
+  - If _T_ is a reference to a class, _S_ includes a reference to the companion object
+    of the class, if it exists, as well as the implicit scopes of all of _T_'s parent classes.
+  - If _T_ is a reference to an object, _S_ includes _T_ itself as well as
+    the implicit scopes of all of _T_'s parent classes.
+  - If _T_ is a reference to an opaque type alias named _A_, _S_ includes
+    a reference to an object _A_ defined in the same scope as the type, if it exists,
+    as well as the implicit scope of _T_'s underlying type or bounds.
+  - If _T_ is a reference to an an abstract type named _A_, _S_ includes
+    a reference to an object _A_ defined in the same scope as the type, if it exists,
+    as well as the implicit scopes of _T_'s lower and upper bound.
+  - If _T_ is a reference to an anchor of the form _p.A_ then _S_ also includes
+    all term references on the path _p_.
+  - If _T_ is some other type, _S_ includes the implicit scopes of all anchors of _T_.
+
+
+
 **4.** The treatment of ambiguity errors has changed. If an ambiguity is encountered in some recursive step of an implicit search, the ambiguity is propagated to the caller.
 
 Example: Say you have the following definitions: