From b5ee289ce63f5b0a173fca9767468e2b3e68f86f Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Mon, 16 Dec 2024 12:52:53 +0300
Subject: [PATCH] proper error for const defines with unsupported types
 [backport:2.0]

fixes #24539
---
 compiler/semfold.nim               |  2 +-
 compiler/semstmts.nim              | 23 +++++++++++++++++++++++
 tests/errmsgs/twrongdefinetype.nim |  4 ++++
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 tests/errmsgs/twrongdefinetype.nim

diff --git a/compiler/semfold.nim b/compiler/semfold.nim
index eb5db88fc9fd6..00b40f57276ea 100644
--- a/compiler/semfold.nim
+++ b/compiler/semfold.nim
@@ -589,7 +589,7 @@ proc foldDefine(m, s: PSym, n: PNode; idgen: IdGenerator; g: ModuleGraph): PNode
             raise newException(ValueError, "invalid enum value: " & str)
         else:
           localError(g.config, s.info, "unsupported type $1 for define '$2'" %
-            [name, typeToString(rawTyp)])
+            [typeToString(rawTyp), name])
       except ValueError as e:
         localError(g.config, s.info,
           "could not process define '$1' of type $2; $3" %
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index f305b3a8295ae..9f6e87f9d47d4 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -612,11 +612,34 @@ proc fillPartialObject(c: PContext; n: PNode; typ: PType) =
   else:
     localError(c.config, n.info, "nkDotNode requires 2 children")
 
+proc checkDefineType(c: PContext; v: PSym; t: PType) =
+  # see semfold.foldDefine for acceptable types
+  let typeKinds =
+    case v.magic
+    of mStrDefine: {tyString, tyCstring}
+    # this used to be not typechecked, so anything that accepts int nodes for compatbility:
+    of mIntDefine: {tyInt..tyInt64, tyUInt..tyUInt64, tyBool, tyChar, tyEnum}
+    of mBoolDefine: {tyBool}
+    of mGenericDefine: {tyString, tyCstring, tyInt..tyInt64, tyUInt..tyUInt64, tyBool, tyEnum}
+    else: raiseAssert("unreachable")
+  if t.skipTypes(abstractVarRange-{tyDistinct}).kind notin typeKinds:
+    let name = 
+      case v.magic
+      of mStrDefine: "strdefine"
+      of mIntDefine: "intdefine"
+      of mBoolDefine: "booldefine"
+      of mGenericDefine: "define"
+      else: raiseAssert("unreachable")
+    localError(c.config, v.info, "unsupported type for constant '" & v.name.s &
+      "' with ." & name & " pragma: " & typeToString(t))
+
 proc setVarType(c: PContext; v: PSym, typ: PType) =
   if v.typ != nil and not sameTypeOrNil(v.typ, typ):
     localError(c.config, v.info, "inconsistent typing for reintroduced symbol '" &
         v.name.s & "': previous type was: " & typeToString(v.typ, preferDesc) &
         "; new type is: " & typeToString(typ, preferDesc))
+  if v.kind == skConst and v.magic in {mGenericDefine, mIntDefine, mStrDefine, mBoolDefine}:
+    checkDefineType(c, v, typ)
   v.typ = typ
 
 proc isPossibleMacroPragma(c: PContext, it: PNode, key: PNode): bool =
diff --git a/tests/errmsgs/twrongdefinetype.nim b/tests/errmsgs/twrongdefinetype.nim
new file mode 100644
index 0000000000000..17e528bd4a4a6
--- /dev/null
+++ b/tests/errmsgs/twrongdefinetype.nim
@@ -0,0 +1,4 @@
+type Foo = object
+const foo {.define.} = Foo() #[tt.Error
+      ^ unsupported type for constant 'foo' with .define pragma: Foo]#
+echo repr(foo)