Add documentation on inline given instances

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -810,7 +810,7 @@ object desugar {
         }
       }
       if mods.isAllOf(Given | Inline | Transparent) then
-        report.error("inline non-alias given cannot be trasparent", cdef)
+        report.error("inline given instances cannot be trasparent", cdef)
       val classMods = if mods.is(Given) then mods &~ (Inline | Transparent) | Synthetic else mods
       cpy.TypeDef(cdef: TypeDef)(
         name = className,

docs/docs/reference/contextual/givens.md

@@ -100,6 +100,21 @@ transparent inline given mkAnnotations[A, T]: Annotations[A, T] = ${
 
 Since `mkAnnotations` is `transparent`, the type of an application is the type of its right-hand side, which can be a proper subtype of the declared result type `Annotations[A, T]`.
 
+Given instances can have the `inline` but not `transparent` modifiers as their type is already known from the signature.
+Example:
+
+```scala
+trait Show[T] {
+  inline def show(x: T): String
+}
+
+inline given Show[Foo] with {
+  /*transparent*/ inline def show(x: Foo): String = ${ ... }
+}
+```
+Note that the inline methods within the given instances may be `transparent`.
+
+
 ## Pattern-Bound Given Instances
 
 Given instances can also appear in patterns. Example: