Fix 22668 - Don't errors when a deprecated method overrides another one

Because both declarations acknowledge that the declaration is deprecated.
This is especially important for libraries that provide a collection of
classes and want to deprecate certain method throughout the entire
class hierarchy.

src/dmd/dsymbolsem.d

@@ -3559,7 +3559,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
                             goto Lintro;
                     }
 
-                    if (fdv.isDeprecated)
+                    if (fdv.isDeprecated && !funcdecl.isDeprecated)
                         deprecation(funcdecl.loc, "`%s` is overriding the deprecated method `%s`",
                                     funcdecl.toPrettyChars, fdv.toPrettyChars);
 
@@ -3814,7 +3814,8 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
                     deprecation(funcdecl.loc,
                                 "`%s` cannot be annotated with `@disable` because it is overriding a function in the base class",
                                 funcdecl.toPrettyChars);
-                if (funcdecl.isDeprecated)
+
+                if (funcdecl.isDeprecated && !(funcdecl.foverrides.length && funcdecl.foverrides[0].isDeprecated))
                     deprecation(funcdecl.loc,
                                 "`%s` cannot be marked as `deprecated` because it is overriding a function in the base class",
                                 funcdecl.toPrettyChars);

test/compilable/deprecated_override.d

@@ -0,0 +1,97 @@
+// https://issues.dlang.org/show_bug.cgi?id=22668
+
+// Overrides with same deprecated'ness are allowed
+
+class SameParent
+{
+    deprecated void foo() {}
+    void foo(int) {}
+
+    void bar(int) {}
+    deprecated void bar() {}
+}
+
+class SameChild : SameParent
+{
+    deprecated override void foo() {}
+    override void foo(int) {}
+
+    override void bar(int) {}
+    deprecated override void bar() {}
+}
+
+/**
+Only the parent declaration is deprecated
+
+TEST_OUTPUT:
+----
+compilable/deprecated_override.d(44): Deprecation: `deprecated_override.IntroducingChild.foo` is overriding the deprecated method `deprecated_override.IntroducingParent.foo`
+compilable/deprecated_override.d(48): Deprecation: `deprecated_override.IntroducingChild.bar` is overriding the deprecated method `deprecated_override.IntroducingParent.bar`
+----
+**/
+
+class IntroducingParent
+{
+    deprecated void foo() {}
+    void foo(int) {}
+
+    void bar(int) {}
+    deprecated void bar() {}
+}
+
+class IntroducingChild : IntroducingParent
+{
+    override void foo() {}
+    override void foo(int) {}
+
+    override void bar(int) {}
+    override void bar() {}
+}
+
+// Unrelated to this path but should this error as well?
+
+class IntroducingGrandchild : IntroducingChild
+{
+    override void foo() {}
+    override void foo(int) {}
+
+    override void bar(int) {}
+    override void bar() {}
+}
+
+/**
+Only the overriding declaration is deprecated
+
+TEST_OUTPUT:
+----
+compilable/deprecated_override.d(83): Deprecation: `deprecated_override.OverrideChild.foo` cannot be marked as `deprecated` because it is overriding a function in the base class
+compilable/deprecated_override.d(87): Deprecation: `deprecated_override.OverrideChild.bar` cannot be marked as `deprecated` because it is overriding a function in the base class
+----
+**/
+
+class OverrideParent
+{
+    void foo() {}
+    void foo(int) {}
+
+    void bar(int) {}
+    void bar() {}
+}
+
+class OverrideChild : OverrideParent
+{
+    deprecated override void foo() {}
+    override void foo(int) {}
+
+    override void bar(int) {}
+    deprecated override void bar() {}
+}
+
+class OverrideGrandChild : OverrideChild
+{
+    deprecated override void foo() {}
+    override void foo(int) {}
+
+    override void bar(int) {}
+    deprecated override void bar() {}
+}