Suggest and infer lifetime annotations (workstream 4)

[usx95]

The idea is to use the lifetime analysis to conclude which parameters escape via return and can be annotated via [[clang::lifetimebound]].

std::string_view Select(bool cond, std::string_view a, std::string_view b) {
  if (cond)
    return a;
  else
    return b;
} 

We can implement this as a clang warning:

std::string_view Select(bool cond, std::string_view a, std::string_view b)
                                   ^^^^^^^^^^^^^ warning: param should be marked [[clang::lifetimebound]]
                                                       ^^^^^^^^^^^^^ warning: param should be marked [[clang::lifetimebound]]

[llvmbot]

@llvm/issue-subscribers-clang-temporal-safety

Author: Utkarsh Saxena (usx95)

The idea is to use the lifetime analysis to conclude which parameters escape via return and can be annotated via `[[clang::lifetimebound]]`.

std::string_view Select(bool cond, std::string_view a, std::string_view b) {
  if (cond)
    return a;
  else
    return b;
} 

We can implement this as a clang warning:

std::string_view Select(bool cond, std::string_view a, std::string_view b)
                                   ^^^^^^^^^^^^^ warning: param should be marked [[clang::lifetimebound]]
                                                       ^^^^^^^^^^^^^ warning: param should be marked [[clang::lifetimebound]]