fixes #21306; fixes #20485; don't transform yields in the var section when introducing new local vars [backport: 1.6] (#21489)

* fixes #21306;  don't transform yields in the var section when introducing new local vars

* adds `inVarSection` so the var section in the var section is freshed

* use `isIntroducingNewLocalVars` to avoid yield transformations in var sections

* fixes comments

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/transf.nim b/compiler/transf.nim
index 7277e6898..445bc1df1 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -50,6 +50,7 @@ type
     module: PSym
     transCon: PTransCon      # top of a TransCon stack
     inlining: int            # > 0 if we are in inlining context (copy vars)
+    isIntroducingNewLocalVars: bool  # true if we are in `introducingNewLocalVars` (don't transform yields)
     contSyms, breakSyms: seq[PSym]  # to transform 'continue' and 'break'
     deferDetected, tooEarly: bool
     graph: ModuleGraph
@@ -450,7 +451,9 @@ proc transformYield(c: PTransf, n: PNode): PNode =
     result.add(c.transCon.forLoopBody)
   else:
     # we need to introduce new local variables:
+    c.isIntroducingNewLocalVars = true # don't transform yields when introducing new local vars
     result.add(introduceNewLocalVars(c, c.transCon.forLoopBody))
+    c.isIntroducingNewLocalVars = false
 
   for idx in 0 ..< result.len:
     var changeNode = result[idx]
@@ -1036,7 +1039,7 @@ proc transform(c: PTransf, n: PNode): PNode =
     else:
       result = transformSons(c, n)
   of nkYieldStmt:
-    if c.inlining > 0:
+    if c.inlining > 0 and not c.isIntroducingNewLocalVars:
       result = transformYield(c, n)
     else:
       result = transformSons(c, n)