[Coin-discuss] Small patch to fix Clang -Wnon-c-typedef-for-linkage in Clp

[Stephan Bergmann]

[I first tried to file this at 
<https://projects.coin-or.org/CoinMP/newticket>, but it says 
"TICKET_CREATE privileges are required to perform this operation on 
Ticket #None. You don't have the required permissions."  Even after I 
created an account there.]

Clang 11 trunk since 
<https://github.com/llvm/llvm-project/commit/7ae1b4a0ce9c7f269cf3069e41496a78e3f28d49> 
"Implement P1766R1: diagnose giving non-C-compatible classes a typedef 
name for linkage purposes" gives a warning about certain

   typedef struct { ... } name;

in C++.  Building CoinMP 1.7.6 as part of building LibreOffice failed with

> In file included from Clp_C_Interface.cpp:192:
> ./Clp_C_Interface.h:15:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
> typedef struct {
>               ^
>                Clp_Solve
> ./Clp_C_Interface.h:15:9: note: type is not C-compatible due to this member declaration
> typedef struct {
>         ^~~~~~
> ./Clp_C_Interface.h:17:3: note: type is given name 'Clp_Solve' for linkage purposes by this typedef declaration
> } Clp_Solve;
>   ^

(see 
<https://gerrit.libreoffice.org/plugins/gitiles/core/+diff/4188c7e2132ec3f1c3e879c179e92ff75c86d24f%5E%21> 
"external/coinmp: -Werror,-Wnon-c-typedef-for-linkage"), and I think 
CoinMP trunk is also affected.  The below patch for Clp should fix it:

> Index: src/Clp_C_Interface.h
> ===================================================================
> --- src/Clp_C_Interface.h	(revision 2650)
> +++ src/Clp_C_Interface.h	(working copy)
> @@ -21,9 +21,9 @@
>  #endif
>  
>  #if defined(CLP_EXTERN_C)
> -typedef struct {
> +struct Clp_Solve {
>    ClpSolve options;
> -} Clp_Solve;
> +};
>  #else
>  typedef void Clp_Solve;
>  #endif