| Issue |
123823
|
| Summary |
[ClangFormat] Space removed in `g< ::f<int>>()` except for `Standard: c++03`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
reventlov
|
In all versions of C++ supported by ClangFormat, [the alternative operator spelling ("digraph") `<:` is treated as `[`](https://en.cppreference.com/w/cpp/language/operator_alternative). However, ClangFormat will remove a space between `<` and `:` (except when `Standard: c++03` is specified, or `Standard: Auto` is specified and no double-closing `>>` is found in the source file):
```c++
g< ::T>(); // before
g<::T>(); // after, compiler error
g [ : T > ( ) ; // C++ equivalent tokenization
```
This causes problems when:
* the first template parameter must use an absolute namespace (e.g., the code is in `f::g`, namespace `f::e` exists, and the parameter is `::e::T`), and
* the code is not compiled with `-fno-digraphs` (or its equivalent in other compilers)
As far as I am aware, this is the only place where the "digraph" alternative spellings can change the meaning of otherwise-valid C++ code (and I believe there is no such case in C, where the digraph operators originated).
There is a (moderately annoying) workaround of adding a dummy comment:
```c++
g</**/ ::T>(); // safe
```
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