From 1c79ef1090a746e516df03d17c2a99117e82bdce Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:32:39 +0800
Subject: [PATCH 1/5] prohibits field variables from being used as lvalues in a
 'fields' loop

---
 compiler/semfields.nim | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 874055cdcde96..7544f012f4c1e 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -17,8 +17,9 @@ type
     field: PSym
     replaceByFieldName: bool
     c: PContext
+    leftPartOfAssign: bool
 
-proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
+proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
   if c.field != nil and isEmptyType(c.field.typ):
     result = newNode(nkEmpty)
     return
@@ -29,6 +30,9 @@ proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     let ident = considerQuotedIdent(c.c, n)
     if c.replaceByFieldName:
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
+        if c.leftPartOfAssign:
+          localError(c.c.config, n.info,
+                    "field variable '$1' is not allowed to use as a lvalue in a 'fields' loop" % [ident.s])
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
                         else: c.tupleType.n[c.tupleIndex].sym.name.s
@@ -37,6 +41,9 @@ proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     # other fields:
     for i in ord(c.replaceByFieldName)..<forLoop.len-2:
       if ident.id == considerQuotedIdent(c.c, forLoop[i]).id:
+        if c.leftPartOfAssign:
+          localError(c.c.config, n.info,
+                    "field variable '$1' is not allowed to use as a lvalue in a 'fields' loop" % [ident.s])
         var call = forLoop[^2]
         var tupl = call[i+1-ord(c.replaceByFieldName)]
         if c.field.isNil:
@@ -48,6 +55,14 @@ proc instFieldLoopBody(c: TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
           result.add(tupl)
           result.add(newSymNode(c.field, n.info))
         break
+  of nkIdentDefs, nkVarTuple, nkConstDef,
+      nkAsgn, nkFastAsgn, nkSinkAsgn:
+    result = shallowCopy(n)
+    c.leftPartOfAssign = true
+    result[0] = instFieldLoopBody(c, n[0], forLoop)
+    c.leftPartOfAssign = false
+    for i in 1..<n.len:
+      result[i] = instFieldLoopBody(c, n[i], forLoop)
   else:
     if n.kind == nkContinueStmt:
       localError(c.c.config, n.info,

From 07463c00fc0a9c1b347b77010e6f2e1a3f62ba33 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:34:45 +0800
Subject: [PATCH 2/5] wordy

---
 compiler/semfields.nim | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 7544f012f4c1e..87b9b4145daa8 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -32,7 +32,7 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
         if c.leftPartOfAssign:
           localError(c.c.config, n.info,
-                    "field variable '$1' is not allowed to use as a lvalue in a 'fields' loop" % [ident.s])
+                    "field variable '$1' is not allowed to be used as a lvalue in a 'fields' loop" % [ident.s])
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
                         else: c.tupleType.n[c.tupleIndex].sym.name.s
@@ -43,7 +43,7 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
       if ident.id == considerQuotedIdent(c.c, forLoop[i]).id:
         if c.leftPartOfAssign:
           localError(c.c.config, n.info,
-                    "field variable '$1' is not allowed to use as a lvalue in a 'fields' loop" % [ident.s])
+                    "field variable '$1' is not allowed to be used as a lvalue in a 'fields' loop" % [ident.s])
         var call = forLoop[^2]
         var tupl = call[i+1-ord(c.replaceByFieldName)]
         if c.field.isNil:

From aca59572c701c3aca769117c90f5473b1c67b6af Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:40:57 +0800
Subject: [PATCH 3/5] oops

---
 compiler/semfields.nim | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 87b9b4145daa8..6e1498a140555 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -30,9 +30,6 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     let ident = considerQuotedIdent(c.c, n)
     if c.replaceByFieldName:
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
-        if c.leftPartOfAssign:
-          localError(c.c.config, n.info,
-                    "field variable '$1' is not allowed to be used as a lvalue in a 'fields' loop" % [ident.s])
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
                         else: c.tupleType.n[c.tupleIndex].sym.name.s

From 8af81e3d246f5272f56a22018ef9cb67d652810a Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:51:19 +0800
Subject: [PATCH 4/5] redefining field variables is disabled

---
 compiler/semfields.nim | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 6e1498a140555..43f159343d1a9 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -17,7 +17,7 @@ type
     field: PSym
     replaceByFieldName: bool
     c: PContext
-    leftPartOfAssign: bool
+    leftPartOfDefinition: bool
 
 proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
   if c.field != nil and isEmptyType(c.field.typ):
@@ -29,6 +29,9 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     result = n
     let ident = considerQuotedIdent(c.c, n)
     if c.replaceByFieldName:
+      if c.leftPartOfDefinition:
+        localError(c.c.config, n.info,
+                  "redefine field variable '$1' in a 'fields' loop" % [ident.s])
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
@@ -38,9 +41,9 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     # other fields:
     for i in ord(c.replaceByFieldName)..<forLoop.len-2:
       if ident.id == considerQuotedIdent(c.c, forLoop[i]).id:
-        if c.leftPartOfAssign:
+        if c.leftPartOfDefinition:
           localError(c.c.config, n.info,
-                    "field variable '$1' is not allowed to be used as a lvalue in a 'fields' loop" % [ident.s])
+                    "redefine field variable '$1' in a 'fields' loop" % [ident.s])
         var call = forLoop[^2]
         var tupl = call[i+1-ord(c.replaceByFieldName)]
         if c.field.isNil:
@@ -52,12 +55,11 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
           result.add(tupl)
           result.add(newSymNode(c.field, n.info))
         break
-  of nkIdentDefs, nkVarTuple, nkConstDef,
-      nkAsgn, nkFastAsgn, nkSinkAsgn:
+  of nkIdentDefs, nkVarTuple, nkConstDef:
     result = shallowCopy(n)
-    c.leftPartOfAssign = true
+    c.leftPartOfDefinition = true
     result[0] = instFieldLoopBody(c, n[0], forLoop)
-    c.leftPartOfAssign = false
+    c.leftPartOfDefinition = false
     for i in 1..<n.len:
       result[i] = instFieldLoopBody(c, n[i], forLoop)
   else:

From 3e6a2a13d9dc729393624c9bc66cda82419b34c8 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:53:56 +0800
Subject: [PATCH 5/5] fixes

---
 compiler/semfields.nim | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/compiler/semfields.nim b/compiler/semfields.nim
index 43f159343d1a9..c13f70e8c467a 100644
--- a/compiler/semfields.nim
+++ b/compiler/semfields.nim
@@ -29,10 +29,10 @@ proc instFieldLoopBody(c: var TFieldInstCtx, n: PNode, forLoop: PNode): PNode =
     result = n
     let ident = considerQuotedIdent(c.c, n)
     if c.replaceByFieldName:
-      if c.leftPartOfDefinition:
-        localError(c.c.config, n.info,
-                  "redefine field variable '$1' in a 'fields' loop" % [ident.s])
       if ident.id == considerQuotedIdent(c.c, forLoop[0]).id:
+        if c.leftPartOfDefinition:
+          localError(c.c.config, n.info,
+                  "redefine field variable '$1' in a 'fields' loop" % [ident.s])
         let fieldName = if c.tupleType.isNil: c.field.name.s
                         elif c.tupleType.n.isNil: "Field" & $c.tupleIndex
                         else: c.tupleType.n[c.tupleIndex].sym.name.s