From 212febef9071e9c4c20ac16ecba5ddc6f5985205 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Sat, 12 Apr 2025 17:25:47 +0300
Subject: [PATCH 1/2] allow setting arbitrary size for importc types

closes #7674
---
 compiler/pragmas.nim | 20 ++++++++++++--------
 compiler/types.nim   | 11 +++++++++++
 doc/manual.md        |  4 ++--
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/compiler/pragmas.nim b/compiler/pragmas.nim
index 51e044ce0bf85..8cf547c9bed93 100644
--- a/compiler/pragmas.nim
+++ b/compiler/pragmas.nim
@@ -947,15 +947,19 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
       of wSize:
         if sym.typ == nil: invalidPragma(c, it)
         var size = expectIntLit(c, it)
-        case size
-        of 1, 2, 4:
-          sym.typ.size = size
-          sym.typ.align = int16 size
-        of 8:
-          sym.typ.size = 8
-          sym.typ.align = floatInt64Align(c.config)
+        if sfImportc in sym.flags:
+          # no restrictions on size for imported types
+          setImportedTypeSize(c.config, sym.typ, size)
         else:
-          localError(c.config, it.info, "size may only be 1, 2, 4 or 8")
+          case size
+          of 1, 2, 4:
+            sym.typ.size = size
+            sym.typ.align = int16 size
+          of 8:
+            sym.typ.size = 8
+            sym.typ.align = floatInt64Align(c.config)
+          else:
+            localError(c.config, it.info, "size may only be 1, 2, 4 or 8")
       of wAlign:
         let alignment = expectIntLit(c, it)
         if isPowerOfTwo(alignment) and alignment > 0:
diff --git a/compiler/types.nim b/compiler/types.nim
index 9853cf1222410..914f57fc8e10b 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -1515,6 +1515,17 @@ proc getSize*(conf: ConfigRef; typ: PType): BiggestInt =
   computeSizeAlign(conf, typ)
   result = typ.size
 
+proc setImportedTypeSize*(conf: ConfigRef, t: PType, size: int) =
+  t.size = size
+  if tfPacked in t.flags or size <= 1:
+    t.align = 1
+  elif size <= 2:
+    t.align = 2
+  elif size <= 4:
+    t.align = 4
+  else:
+    t.align = floatInt64Align(conf)
+
 proc isConcept*(t: PType): bool=
   case t.kind
   of tyConcept: true
diff --git a/doc/manual.md b/doc/manual.md
index 8eab6683d5f51..9abd0e762c8d6 100644
--- a/doc/manual.md
+++ b/doc/manual.md
@@ -7815,6 +7815,8 @@ The `size pragma` allows specifying the size of the enum type.
   doAssert sizeof(EventType) == sizeof(uint32)
   ```
 
+When used for enum types, the `size pragma` accepts only the values 1, 2, 4 or 8.
+
 The `size pragma` can also specify the size of an `importc` incomplete object type
 so that one can get the size of it at compile time even if it was declared without fields.
 
@@ -7827,8 +7829,6 @@ so that one can get the size of it at compile time even if it was declared witho
       echo sizeof(AtomicFlag)
   ```
 
-The `size pragma` accepts only the values 1, 2, 4 or 8.
-
 
 Align pragma
 ------------

From 81a3223a839dae2694135e6a20840ead7f3abb92 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Sat, 12 Apr 2025 17:30:53 +0300
Subject: [PATCH 2/2] add not very rigorous test

---
 tests/c/timportedsize.nim | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 tests/c/timportedsize.nim

diff --git a/tests/c/timportedsize.nim b/tests/c/timportedsize.nim
new file mode 100644
index 0000000000000..4541ac51d39d9
--- /dev/null
+++ b/tests/c/timportedsize.nim
@@ -0,0 +1,10 @@
+{.emit: """
+typedef struct Foo {
+  NI64 a;
+  NI64 b;
+} Foo;
+""".}
+
+type Foo {.importc: "Foo", size: 16.} = object
+
+var x: Foo