concept patch: inheritance (#25317)

adds some inheritance support

---------

Co-authored-by: Andreas Rumpf <araq4k@proton.me>

compiler/concepts.nim

@@ -263,6 +263,22 @@ proc conceptsMatch(c: PContext, fc, ac: PType; m: var MatchCon): MatchKind =
       return mkNoMatch
   return mkSubset
 
+proc isObjectSubtype(f, a: PType): bool =
+  var t = a
+  result = false
+  while t != nil:
+    t = t.baseClass
+    if t == nil:
+      break
+    t = t.skipTypes({tyPtr,tyRef})
+    if t == nil:
+      break
+    if t.kind != tyObject:
+      break
+    if sameObjectTypes(f, t):
+      result = true
+      break
+
 proc matchType(c: PContext; fo, ao: PType; m: var MatchCon): bool =
   ## The heart of the concept matching process. 'f' is the formal parameter of some
   ## routine inside the concept that we're looking for. 'a' is the formal parameter
@@ -327,6 +343,8 @@ proc matchType(c: PContext; fo, ao: PType; m: var MatchCon): bool =
         result = a.base.sym == f.sym
       else:
         result = sameType(f, a)
+      if not result and f.kind == tyObject and a.kind == tyObject:
+        result = isObjectSubtype(f, a)
   of tyEmpty, tyString, tyCstring, tyPointer, tyNil, tyUntyped, tyTyped, tyVoid:
     result = a.skipTypes(ignorableForArgType).kind == f.kind
   of tyBool, tyChar, tyInt..tyUInt64:

doc/manual.md

@@ -3008,6 +3008,12 @@ is more specific
 2. if the concept is being compared with another concept the result is deferred to [Concept subset matching]
 3. in any other case the concept is less specific then it's competitor 
 
+Currently, the concept evaluation mechanism evaluates to a successful match on the first acceptable candidate
+for each defined binding. This has a couple of notable effects:
+
+- generic parameters are fulfilled by the first candidate match even if other candidates would also match and bind different parameters
+- inheritable objects match as they do in normal overload resolution except the "depth" is not accounted for, because that would require calculating the minimum depth of any matching binding
+
 
 Concept subset matching
 -------------------------

tests/concepts/tconceptsv2.nim

@@ -585,3 +585,18 @@ block:
     discard
 
   assert (ref AObj[int]) is C
+
+block:
+  type 
+    C = concept
+      proc x(a:Self, x: int)
+    StreamObj = object of RootObj
+    Stream = ref StreamObj
+    MemMapFileStreamObj = object of Stream
+    MemMapFileStream = ref MemMapFileStreamObj
+
+  proc x(a: Stream, x: int) = discard
+  proc spring(x: C) = discard
+
+  let test = MemMapFileStream()
+  spring(test)