From 7366a3da37605b230823dd4b6db07abb70dbd40b Mon Sep 17 00:00:00 2001
From: Saem Ghani <saemghani+github@gmail.com>
Date: Wed, 24 Mar 2021 03:55:58 -0700
Subject: [PATCH] potential fix for semgeneric formal params (#17494)

marked locations where analysis of return formal param is done prior to
args. This might fix some subtle bugs.
---
 compiler/isolation_check.nim | 3 +++
 compiler/reorder.nim         | 1 +
 compiler/semgnrc.nim         | 6 ++++--
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/compiler/isolation_check.nim b/compiler/isolation_check.nim
index 9c8ca58b4a..43db5d59b0 100644
--- a/compiler/isolation_check.nim
+++ b/compiler/isolation_check.nim
@@ -85,6 +85,9 @@ proc checkIsolate*(n: PNode): bool =
     of nkCharLit..nkNilLit:
       result = true
     of nkCallKinds:
+      # XXX: as long as we don't update the analysis while examining arguments
+      #      we can do an early check of the return type, otherwise this is a
+      #      bug and needs to be moved below
       if n[0].typ.flags * {tfGcSafe, tfNoSideEffect} == {}:
         return false
       for i in 1..<n.len:
diff --git a/compiler/reorder.nim b/compiler/reorder.nim
index d2b89f3921..4ffe4ccf8c 100644
--- a/compiler/reorder.nim
+++ b/compiler/reorder.nim
@@ -107,6 +107,7 @@ proc computeDeps(cache: IdentCache; n: PNode, declares, uses: var IntSet; topLev
       for i in 0..<n.safeLen: deps(n[i])
   of nkMixinStmt, nkBindStmt: discard
   else:
+    # XXX: for callables, this technically adds the return type dep before args
     for i in 0..<n.safeLen: deps(n[i])
 
 proc hasIncludes(n:PNode): bool =
diff --git a/compiler/semgnrc.nim b/compiler/semgnrc.nim
index dfbb022c89..615413fc6d 100644
--- a/compiler/semgnrc.nim
+++ b/compiler/semgnrc.nim
@@ -452,8 +452,6 @@ proc semGenericStmt(c: PContext, n: PNode,
     discard
   of nkFormalParams:
     checkMinSonsLen(n, 1, c.config)
-    if n[0].kind != nkEmpty:
-      n[0] = semGenericStmt(c, n[0], flags+{withinTypeDesc}, ctx)
     for i in 1..<n.len:
       var a = n[i]
       if (a.kind != nkIdentDefs): illFormedAst(a, c.config)
@@ -462,6 +460,10 @@ proc semGenericStmt(c: PContext, n: PNode,
       a[^1] = semGenericStmt(c, a[^1], flags, ctx)
       for j in 0..<a.len-2:
         addTempDecl(c, getIdentNode(c, a[j]), skParam)
+    # XXX: last change was moving this down here, search for "1.." to keep
+    #      going from this file onward
+    if n[0].kind != nkEmpty:
+      n[0] = semGenericStmt(c, n[0], flags+{withinTypeDesc}, ctx)
   of nkProcDef, nkMethodDef, nkConverterDef, nkMacroDef, nkTemplateDef,
      nkFuncDef, nkIteratorDef, nkLambdaKinds:
     checkSonsLen(n, bodyPos + 1, c.config)