It's not so common knowledge that forges also expose pull requests as
git refs. But it's actually a cool way of quickly testing someones
contribution, so I found it worth specifically mentioning it.
It seems that I copied the expression for baseDir thoughtlessly and
did not come back to it.
- `baseDir` was only used in the `fromArgs` branch.
- `fromArgs` is true when `packages` is true.
This interferes with the progress bar, resulting in output like
evaluating derivation 'git+file:///home/eelco/Dev/nix-master#packages.x86_64-linux.default'/nix/store/zz8v96j5md952x0mxfix12xqnvq5qv5x-nix-2.26.0pre20241114_a95f6ea.drv
This patch gets rid of UB when verbosity exceeds the maximum logging value of `lvlVomit = 7` and
reaches invalid values (e.g. 8). This is actually triggered in functional tests.
There are too many occurrences to list, but here's one from the UBSAN log:
../src/libstore/gc.cc:610:5: runtime error: load of value 8, which is not a valid value for type 'Verbosity'
This was first tagged as 2.15.0, 1½ years ago; plenty of time for
everyone to catch up.
By now, the warning is causing more confusion than that it is helpful,
because passing a `.drv` or `drvPath` has legitimate use cases.
In these trivial cases the final vector size (or lower bound on the size) is known,
so we can avoid some vector reallocations. This is not very important, but is just
good practice and general hygiene.
This is good practice to avoid pessimisations.
Left comments for the reasoning why ctors should be noexcept.
There are some tricky cases where we intentionally want throwing move ctors/assignments.
But those cases should really be reviewed, since some of those can be replaced
with more idiomatic copy/move-and-swap.
`auto &&` and `T &&` are forwarding references and can be
either lvalue or rvalue references. Moving from universal references
is incorrect and should not be done.
Moving from integral or floating-point values is pointless and just
worsens debug performance.
Naming class member variables the same as constructor arguments is a very
slippery slope because of how member variable names get resolved. Compiler
is not very helpful here and we need static analysis to forbid this kind of
stuff.
The following example illustrates the cause quite well:
```cpp
struct B {
B(int) {}
};
struct A {
A(int b): b([&](){
return b;
static_assert(std::is_same_v<decltype(b), int>);
}()) {
static_assert(std::is_same_v<decltype(b), int>);
}
void member() {
static_assert(std::is_same_v<decltype(b), B>);
}
B b;
};
int main() {
A(1).member();
}
```
From N4861 6.5.1 Unqualified name lookup:
> In all the cases listed in [basic.lookup.unqual], the scopes are searched
> for a declaration in the order listed in each of the respective categories;
> name lookup ends as soon as a declaration is found for the name.
> If no declaration is found, the program is ill-formed.
In the affected code there was a use-after-move for all accesses in the constructor
body, but this UB wasn't triggered.
These types of errors are trivial to catch via clang-tidy's [clang-analyzer-cplusplus.Move].
Robert Hensing