delay markUsed for converters until call is resolved (#24243)

fixes #24241

(cherry picked from commit 09043f409f)

compiler/sem.nim

@@ -89,6 +89,11 @@ proc fitNodePostMatch(c: PContext, formal: PType, arg: PNode): PNode =
     changeType(c, x, formal, check=true)
   result = arg
   result = skipHiddenSubConv(result, c.graph, c.idgen)
+  # mark inserted converter as used:
+  var a = result
+  if a.kind == nkHiddenDeref: a = a[0]
+  if a.kind == nkHiddenCallConv and a[0].kind == nkSym:
+    markUsed(c, a.info, a[0].sym)
 
 
 proc fitNode(c: PContext, formal: PType, arg: PNode; info: TLineInfo): PNode =

compiler/semcall.nim

@@ -645,6 +645,15 @@ proc instGenericConvertersSons*(c: PContext, n: PNode, x: TCandidate) =
     for i in 1..<n.len:
       instGenericConvertersArg(c, n[i], x)
 
+proc markConvertersUsed*(c: PContext, n: PNode) =
+  assert n.kind in nkCallKinds
+  for i in 1..<n.len:
+    var a = n[i]
+    if a == nil: continue
+    if a.kind == nkHiddenDeref: a = a[0]
+    if a.kind == nkHiddenCallConv and a[0].kind == nkSym:
+      markUsed(c, a.info, a[0].sym)
+
 proc indexTypesMatch(c: PContext, f, a: PType, arg: PNode): PNode =
   var m = newCandidate(c, f)
   result = paramTypesMatch(m, f, a, arg, nil)
@@ -809,6 +818,7 @@ proc semResolvedCall(c: PContext, x: var TCandidate,
 
   result = x.call
   instGenericConvertersSons(c, result, x)
+  markConvertersUsed(c, result)
   result[0] = newSymNode(finalCallee, getCallLineInfo(result[0]))
   if finalCallee.magic notin {mArrGet, mArrPut}:
     result.typ = finalCallee.typ.returnType

compiler/semexprs.nim

@@ -1236,6 +1236,7 @@ proc semIndirectOp(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
     else:
       result = m.call
       instGenericConvertersSons(c, result, m)
+      markConvertersUsed(c, result)
 
   else:
     result = overloadedCallOpr(c, n) # this uses efNoUndeclared

compiler/sigmatch.nim

@@ -2299,7 +2299,9 @@ proc userConvMatch(c: PContext, m: var TCandidate, f, a: PType,
       dest = generateTypeInstance(c, m.bindings, arg, dest)
     let fdest = typeRel(m, f, dest)
     if fdest in {isEqual, isGeneric} and not (dest.kind == tyLent and f.kind in {tyVar}):
-      markUsed(c, arg.info, c.converters[i])
+      # can't fully mark used yet, may not be used in final call
+      incl(c.converters[i].flags, sfUsed)
+      markOwnerModuleAsUsed(c, c.converters[i])
       var s = newSymNode(c.converters[i])
       s.typ = c.converters[i].typ
       s.info = arg.info

tests/converter/tdeprecatedconverter.nim

@@ -0,0 +1,14 @@
+# issue #24241
+
+{.warningAsError[Deprecated]: on.}
+
+type X = distinct int
+
+converter toInt(x: X): int{.deprecated.} = int(x)
+
+template `==`(a, b: X): bool = false # this gets called so we didn't convert
+
+doAssert not (X(1) == X(2))
+doAssert not compiles(X(1) + X(2))
+doAssert not (compiles do:
+  let x: int = X(1))