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Objects containing `importc` fields without `completeStruct` fail to compile when used as const/static. The C codegen generates "aggregate initialization" which is invalid for opaque types. Fixes #25405. Nim code: ```nim type OpaqueInt {.importc: "_Atomic int", nodecl.} = object ContainsImportc = object normal: int opaque: OpaqueInt const c = default(ContainsImportc) ``` Resulting C code: ```c // Invalid C - cannot aggregate-init opaque type NIM_CONST ContainsImportc c = {((NI) 0), {}}; ^^ error: illegal initializer type ``` ## Solution Fix in `ccgexprs.nim`: 1. Skip opaque importc fields when building aggregate initializers 2. Use "designated initializers" (`siNamedStruct`) when opaque fields are present to avoid positional misalignment ```c // Valid C: // - opaque field is omitted and implicitly zero-initialized by C // - other fields are explitly named and initialized NIM_CONST ContainsImportc c = {.normal = ((NI) 0)}; ``` This correctly handles the case where the opaque fields might be in any order. A field is considered "opaque importc" if: - Has `sfImportc` flag - Does NOT have `tfCompleteStruct` flag - Either has `tfIncompleteStruct` OR is an object with no visible fields The `containsOpaqueImportcField` proc recursively checks all object fields, including nested objects and variant branches. Anonymous unions (from variant objects) are handled by passing an empty field name, which skips the `.fieldname = ` prefix since C anonymous unions have no field name. Note that initialization for structs without opaque importc fields remains the same as before this changeset. ## Test Coverage `tests/ccgbugs/timportc_field_init.nim` covers: - Simple struct with one importc field - Nested struct containing struct with importc field - Variant object (case object) with importc field in a branch - Array of structs with importc fields - Tuple containing struct with importc field - `completeStruct` importc types (still use aggregate init) - Sandwich case (opaque field between two non-opaque fields) - Fields with different C names (`{.importc: "c_name".}`, `{.exportc.}`) - `{.packed.}` structs with opaque fields - `{.union.}` types with opaque fields - Deep nesting (3+ levels) - Multiple opaque fields with renamed fields between them