fixes #25290; tempalte overload scope dupe (#25308)

#25290
drafted bc if this passes full CI I am going to try and remove that
weird stuff in `pickBestCandidate`

(cherry picked from commit 2501e23d81)

compiler/semcall.nim

@@ -131,7 +131,7 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
   var sym = syms[0].s
   let name = sym.name
   var scope = syms[0].scope
-
+  c.openShadowScope
   if allowTypeBoundOps:
     for a in 1 ..< n.len:
       # for every already typed argument, add type bound ops
@@ -218,6 +218,10 @@ proc pickBestCandidate(c: PContext, headSymbol: PNode,
     scope = syms[nextSymIndex].scope
     inc(nextSymIndex)
 
+  if best.state == csMatch and best.calleeSym != nil and best.calleeSym.kind in {skTemplate, skMacro}:
+    c.closeShadowScope
+  else:
+    c.mergeShadowScope
 
 proc effectProblem(f, a: PType; result: var string; c: PContext) =
   if f.kind == tyProc and a.kind == tyProc:

compiler/sigmatch.nim

@@ -2835,9 +2835,11 @@ proc findFirstArgBlock(m: var TCandidate, n: PNode): int =
     else: break
 
 proc matchesAux(c: PContext, n, nOrig: PNode, m: var TCandidate, marker: var IntSet) =
-
   template noMatch() =
-    c.mergeShadowScope #merge so that we don't have to resem for later overloads
+    if m.calleeSym != nil and m.calleeSym.kind notin {skTemplate, skMacro}:
+      c.mergeShadowScope
+    else:
+      c.closeShadowScope
     m.state = csNoMatch
     m.firstMismatch.arg = a
     m.firstMismatch.formal = formal

tests/overload/t25290.nim

@@ -0,0 +1,34 @@
+proc temp(one: int, two: int, three: int)  =
+  discard
+
+template temp(body: untyped): untyped =
+  body
+
+temp:
+  proc a(tp: int) =
+    discard
+
+proc mixedTemp(x: int) =
+  discard
+
+proc mixedTemp(x: bool) =
+  discard
+
+template mixedTemp(body: untyped): untyped =
+  body
+
+# The `bool` proc should win here so `xx` survives
+mixedTemp (let xx = 1; true)
+discard xx
+
+proc sinkTemp(x: int) =
+  discard
+
+template sinkTemp(body: untyped): untyped =
+  discard
+
+# Here the template should win here so `let xy` is sunk into template as AST
+sinkTemp (let xy = "template"; xy)
+
+when declared(xy):
+  {.error: "xy leaked from failed proc candidate".}