fixes #26000; Cannot add members to enum-indexed array of seqs at compile time

compiler/vmgen.nim

@@ -851,14 +851,26 @@ proc genBinaryStmt(c: PCtx; n: PNode; opc: TOpcode) =
   c.freeTemp(tmp)
   c.freeTemp(dest)
 
+proc genMutatingValue(c: PCtx; n: PNode): TRegister =
+  ## Loads the value of an in-place mutation target while keeping it attached to
+  ## its original storage. Compound lvalues must be resolved through their
+  ## address: a normal value load can return a detached copy (for example, when
+  ## indexing a broadcast default array).
+  if needsAsgnPatch(n):
+    let address = c.genx(n, {gfNodeAddr})
+    result = c.getTemp(n.typ)
+    c.gABC(n, opcLdDeref, result, address)
+    c.freeTemp(address)
+  else:
+    result = c.genx(n)
+
 proc genBinaryStmtVar(c: PCtx; n: PNode; opc: TOpcode) =
   var x = n[1]
   if x.kind in {nkAddr, nkHiddenAddr}: x = x[0]
   let
-    dest = c.genx(x)
+    dest = c.genMutatingValue(x)
     tmp = c.genx(n[2])
   c.gABC(n, opc, dest, tmp, 0)
-  #c.genAsgnPatch(n[1], dest)
   c.freeTemp(tmp)
   c.freeTemp(dest)
 
@@ -1160,12 +1172,20 @@ proc genMagic(c: PCtx; n: PNode; dest: var TDest; flags: TGenFlags = {}, m: TMag
     c.freeTemp(right)
     c.freeTemp(d)
 
-  of mIncl, mExcl:
+  of mIncl:
+    unused(c, n, dest)
+    var d = c.genMutatingValue(n[1])
+    var tmp = c.genx(n[2])
+    c.genSetType(n[1], d)
+    c.gABC(n, opcIncl, d, tmp)
+    c.freeTemp(d)
+    c.freeTemp(tmp)
+  of mExcl:
     unused(c, n, dest)
     var d = c.genx(n[1])
     var tmp = c.genx(n[2])
     c.genSetType(n[1], d)
-    c.gABC(n, if m == mIncl: opcIncl else: opcExcl, d, tmp)
+    c.gABC(n, opcExcl, d, tmp)
     c.freeTemp(d)
     c.freeTemp(tmp)
   of mCard: genCard(c, n, dest)

tests/vm/tbroadcastarraymutation.nim

@@ -0,0 +1,101 @@
+type
+  Container = object
+    numbers: seq[int]
+    text: string
+    chars: set[char]
+
+  Variant = object
+    case enabled: bool
+    of false:
+      numbers: seq[int]
+    else:
+      discard
+
+  Index = enum
+    index0, index1, index2, index3, index4, index5, index6, index7,
+    index8, index9, index10, index11, index12, index13, index14, index15,
+    index16, index17, index18, index19, index20, index21, index22, index23,
+    index24, index25, index26, index27, index28, index29, index30, index31,
+    index32
+
+  Outer = object
+    values: array[33, seq[int]]
+
+proc directSeq(): array[33, seq[int]] =
+  result[32].add 1
+
+proc directStringChar(): array[33, string] =
+  result[32].add 'a'
+
+proc directStringString(): array[33, string] =
+  result[32].add "ab"
+
+proc directSet(): array[33, set[char]] =
+  result[32].incl 'a'
+
+proc fieldSeq(): array[33, Container] =
+  result[32].numbers.add 1
+
+proc fieldStringChar(): array[33, Container] =
+  result[32].text.add 'a'
+
+proc fieldStringString(): array[33, Container] =
+  result[32].text.add "ab"
+
+proc fieldSet(): array[33, Container] =
+  result[32].chars.incl 'a'
+
+proc nestedSeq(): array[33, array[33, seq[int]]] =
+  result[32][32].add 1
+
+proc checkedFieldSeq(): array[33, Variant] =
+  result[32].numbers.add 1
+
+proc enumIndexSeq(): array[Index, seq[int]] =
+  result[index32].add 1
+
+proc rangeIndexSeq(): array[10..42, seq[int]] =
+  result[42].add 1
+
+proc firstIndexSeq(): array[33, seq[int]] =
+  result[0].add 1
+
+proc middleIndexSeq(): array[33, seq[int]] =
+  result[16].add 1
+
+proc objectArraySeq(): Outer =
+  result.values[32].add 1
+
+proc singleEvaluation(): tuple[values: array[33, seq[int]], evaluations: int] =
+  var evaluations = 0
+  proc index(): int =
+    inc evaluations
+    32
+  result.values[index()].add 1
+  result.evaluations = evaluations
+
+proc test =
+  let direct = directSeq()
+  doAssert direct[0].len == 0
+  doAssert direct[31].len == 0
+  doAssert direct[32] == @[1]
+  doAssert directStringChar()[32] == "a"
+  doAssert directStringString()[32] == "ab"
+  doAssert 'a' in directSet()[32]
+  doAssert fieldSeq()[32].numbers == @[1]
+  doAssert fieldStringChar()[32].text == "a"
+  doAssert fieldStringString()[32].text == "ab"
+  doAssert 'a' in fieldSet()[32].chars
+  doAssert nestedSeq()[32][32] == @[1]
+  doAssert checkedFieldSeq()[32].numbers == @[1]
+  doAssert enumIndexSeq()[index32] == @[1]
+  doAssert rangeIndexSeq()[42] == @[1]
+  doAssert firstIndexSeq()[0] == @[1]
+  doAssert middleIndexSeq()[16] == @[1]
+  doAssert objectArraySeq().values[32] == @[1]
+  let evaluated = singleEvaluation()
+  doAssert evaluated.values[32] == @[1]
+  doAssert evaluated.evaluations == 1
+
+static: test()
+test()