fixes #17681; enforce codegen for exportc consts (#24546)

fixes #17681

(cherry picked from commit d5c7abe3d2)

compiler/ccgexprs.nim

@@ -3111,6 +3111,12 @@ proc expr(p: BProc, n: PNode, d: var TLoc) =
   of nkConstSection:
     if useAliveDataFromDce in p.module.flags:
       genConstStmt(p, n)
+    else: # enforce addressable consts for exportc
+      let m = p.module
+      for it in n:
+        let symNode = skipPragmaExpr(it[0])
+        if symNode.kind == nkSym and sfExportc in symNode.sym.flags:
+          requestConstImpl(p, symNode.sym)
     # else: consts generated lazily on use
   of nkForStmt: internalError(p.config, n.info, "for statement not eliminated")
   of nkCaseStmt: genCase(p, n, d)

tests/consts/taddressable_consts.nim

@@ -0,0 +1,26 @@
+discard """
+  joinable: false
+"""
+
+block:
+  proc magics(): array[3, int] =
+    result = [1, 2, 3]
+
+
+  const magic_arrays {.exportc.} = magics()
+
+  let sss {.importc: "magic_arrays", nodecl.} : array[3, int]
+
+
+  doAssert sss[2] == 3
+
+block:
+  proc magics(): int =
+    result = 12
+
+
+  const magic_numbers {.exportc.} = magics()
+
+  let sss {.importc: "magic_numbers", nodecl.} : int
+
+  doAssert sss == 12

tests/consts/taddressable_consts2.nim

@@ -0,0 +1,24 @@
+discard """
+  joinable: false
+"""
+
+block:
+
+  const magic_numbers {.exportc.} = 12
+
+  let sss {.importc: "magic_numbers", nodecl.} : int
+
+  doAssert magic_numbers == 12
+  doAssert sss == 12
+
+block:
+  proc magics(): array[3, int] =
+    result = [1, 2, 3]
+
+
+  const magic_arrays {.exportc.} = magics()
+
+  let sss {.importc: "magic_arrays", nodecl.} : array[3, int]
+
+  doAssert magic_arrays[1] == 2
+  doAssert sss[2] == 3