TEMPLATE_TEST_CASE triggers -Wstring-plus-int

[michaelvlach]

Describe the bug
Clang and clang-tidy warns with -Wstring-plus-int whenever TEMPLATE_TEST_CASE is used. It triggers with any template argument (not just int).

The warning message:

adding 'int' to a string doees not append to the string

Suggested fix:

use array indexing to silence this warning

Expected behavior
TEMPLATE_TEST_CASE does not generate -Wstring-plus-int warning.

Reproduction steps

1. Use clang or clang-tidy.
2. Compile either TEMPLATE_TEST_CASE example -OR- following minimal:

TEMPLATE_TEST_CASE("", "", int)
{
}

Platform information:

• OS: Windows 10
• Compiler+version: clang9, clang-tidy9
• Catch version: v1.2.10

Additional context
I cannot pinpoint the exact location in the code that triggers this because the warning stack exceeds its limits for macro expansions but I reckon people familiar with the Catch2 internals would have a good idea what might be the issue that triggers this.

It will be something like "mystring" + 1 or somesuch. And the fix is to advance address of the string, not the string itself, e.g. &"mystring"[1].

See live demo: https://godbolt.org/z/TkaTSV

[horenmar]

Can't reproduce with Clang

$ cat 1806.cpp
#define CATCH_CONFIG_MAIN
#include "catch.hpp"

TEMPLATE_TEST_CASE("", "", int) {}
$ clang++ --version
clang version 10.0.0-svn375026-1~exp1+0~20191016181515.2549~1.gbp364367 (trunk)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
$ clang++ -std=c++11 1806.cpp -Wstring-plus-int
$

[michaelvlach]

I cannot reproduce on Ubuntu 19.04 with clang++-9 or with clang-tidy-9 either but on Windows 10 with LLVM 9.0 installed I can reproduce it:

C:\dev\projects\ADev\tools>clang++ --version
clang version 9.0.0 (tags/RELEASE_900/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin

Then compilation (of the same file as you did):

C:\dev\projects\ADev\tools>clang++ test.cpp
test.cpp:4:1: warning: adding 'int' to a string does not append to the string [-Wstring-plus-int]
TEMPLATE_TEST_CASE("", "", int) {}
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./Catch2/single_include/catch2/catch.hpp:17356:64: note: expanded from macro 'TEMPLATE_TEST_CASE'
#define TEMPLATE_TEST_CASE( ... ) INTERNAL_CATCH_EXPAND_VARGS( INTERNAL_CATCH_TEMPLATE_TEST_CASE( __VA_ARGS__ ) )
                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./Catch2/single_include/catch2/catch.hpp:1098:38: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_TEST_CASE'
        INTERNAL_CATCH_EXPAND_VARGS( INTERNAL_CATCH_TEMPLATE_TEST_CASE_2( INTERNAL_CATCH_UNIQUE_NAME( ____C_A_T_...
                                     ^
./Catch2/single_include/catch2/catch.hpp:1079:74: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_TEST_CASE_2'
                    constexpr char const* tmpl_types[] = {CATCH_REC_LIST(INTERNAL_CATCH_STRINGIZE_WITHOUT_PARENS...
                                                                         ^
note: (skipping 2189 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
./Catch2/single_include/catch2/catch.hpp:670:37: note: expanded from macro 'CATCH_RECURSION_LEVEL0'
#define CATCH_RECURSION_LEVEL0(...) __VA_ARGS__
                                    ^
./Catch2/single_include/catch2/catch.hpp:678:42: note: expanded from macro 'INTERNAL_CATCH_EXPAND_VARGS'
#define INTERNAL_CATCH_EXPAND_VARGS(...) __VA_ARGS__
                                         ^
./Catch2/single_include/catch2/catch.hpp:678:42: note: expanded from macro 'INTERNAL_CATCH_EXPAND_VARGS'
#define INTERNAL_CATCH_EXPAND_VARGS(...) __VA_ARGS__
                                         ^~~~~~~~~~~
test.cpp:4:1: note: use array indexing to silence this warning
./Catch2/single_include/catch2/catch.hpp:17356:64: note: expanded from macro 'TEMPLATE_TEST_CASE'
#define TEMPLATE_TEST_CASE( ... ) INTERNAL_CATCH_EXPAND_VARGS( INTERNAL_CATCH_TEMPLATE_TEST_CASE( __VA_ARGS__ ) )
                                                               ^
./Catch2/single_include/catch2/catch.hpp:1098:38: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_TEST_CASE'
        INTERNAL_CATCH_EXPAND_VARGS( INTERNAL_CATCH_TEMPLATE_TEST_CASE_2( INTERNAL_CATCH_UNIQUE_NAME( ____C_A_T_...
                                     ^
./Catch2/single_include/catch2/catch.hpp:1079:74: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_TEST_CASE_2'
                    constexpr char const* tmpl_types[] = {CATCH_REC_LIST(INTERNAL_CATCH_STRINGIZE_WITHOUT_PARENS...

The clang-tidy is the same story, only on Windows 10 it produces this same warning (among others).

[horenmar]

Right, it seems that Clang actually masks itself for MSVC well enough to get the path for MSVC's old preprocessor, which contains this

#define INTERNAL_CATCH_STRINGIZE_WITHOUT_PARENS(param) (INTERNAL_CATCH_STRINGIZE(INTERNAL_CATCH_REMOVE_PARENS(param)) + 1)

because the preprocessor just prepends a space when expanding the argument with #__VA_ARGS__.