From 0869d2a47777685d221ddde927f0175096c911b0 Mon Sep 17 00:00:00 2001
From: flywind <43030857+xflywind@users.noreply.github.com>
Date: Wed, 18 Nov 2020 08:14:14 +0800
Subject: [PATCH] fix #15972 (#15994)

* fix #15972

* add testcase

* more
---
 compiler/semstmts.nim                            |  4 ++--
 .../stmt/tforloop_tuple_multiple_underscore.nim  | 10 ++++++++++
 tests/stmt/tforloop_tuple_underscore.nim         | 16 ++++++++++++++++
 tests/stmt/tforloop_underscore.nim               |  6 ++++++
 4 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 tests/stmt/tforloop_tuple_multiple_underscore.nim
 create mode 100644 tests/stmt/tforloop_tuple_underscore.nim
 create mode 100644 tests/stmt/tforloop_underscore.nim

diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index f83864775afef..cd7428b627ea0 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -739,7 +739,7 @@ proc semForVars(c: PContext, n: PNode; flags: TExprFlags): PNode =
           else:
             v.typ = iter[i]
           n[0][i] = newSymNode(v)
-          if sfGenSym notin v.flags: addDecl(c, v)
+          if sfGenSym notin v.flags and not isDiscardUnderscore(v): addDecl(c, v)
           elif v.owner == nil: v.owner = getCurrOwner(c)
       else:
         var v = symForVar(c, n[0])
@@ -749,7 +749,7 @@ proc semForVars(c: PContext, n: PNode; flags: TExprFlags): PNode =
         # for an example:
         v.typ = iterBase
         n[0] = newSymNode(v)
-        if sfGenSym notin v.flags: addDecl(c, v)
+        if sfGenSym notin v.flags and not isDiscardUnderscore(v): addDecl(c, v)
         elif v.owner == nil: v.owner = getCurrOwner(c)
     else:
       localError(c.config, n.info, errWrongNumberOfVariables)
diff --git a/tests/stmt/tforloop_tuple_multiple_underscore.nim b/tests/stmt/tforloop_tuple_multiple_underscore.nim
new file mode 100644
index 0000000000000..2afdb0b7706c5
--- /dev/null
+++ b/tests/stmt/tforloop_tuple_multiple_underscore.nim
@@ -0,0 +1,10 @@
+discard """
+  errormsg: "undeclared identifier: '_'"
+"""
+
+iterator iter(): (int, int, int) =
+  yield (1, 1, 2)
+
+
+for (_, i, _) in iter():
+  echo _
\ No newline at end of file
diff --git a/tests/stmt/tforloop_tuple_underscore.nim b/tests/stmt/tforloop_tuple_underscore.nim
new file mode 100644
index 0000000000000..8cbb0fc10905d
--- /dev/null
+++ b/tests/stmt/tforloop_tuple_underscore.nim
@@ -0,0 +1,16 @@
+discard """
+  errormsg: "undeclared identifier: '_'"
+"""
+
+iterator iter(): (int, int) =
+  yield (1, 2)
+  yield (3, 4)
+  yield (1, 2)
+  yield (3, 4)
+  yield (1, 2)
+  yield (3, 4)
+
+
+for (_, i) in iter():
+  echo _
+
diff --git a/tests/stmt/tforloop_underscore.nim b/tests/stmt/tforloop_underscore.nim
new file mode 100644
index 0000000000000..c5b49da778d3c
--- /dev/null
+++ b/tests/stmt/tforloop_underscore.nim
@@ -0,0 +1,6 @@
+discard """
+  errormsg: "undeclared identifier: '_'"
+"""
+
+for _ in ["a"]:
+  echo _