Good to explicitly declare things to not accidentally do twice the work by
preventing that kind of misuse.
This is essentially just cppcoreguidelines-special-member-functions lint
in clang-tidy.
When deepSeq encounters an error while evaluating a list element, the
error trace now includes the list index, making it easier to locate
the problematic element.
builtins.deepSeq on deeply nested structures (e.g., a linked list with
100,000 elements) caused an uncontrolled OS-level stack overflow with
no Nix stack trace.
Fix by adding call depth tracking to forceValueDeep, integrating with
Nix's existing max-call-depth mechanism. Now produces a controlled
"stack overflow; max-call-depth exceeded" error with a proper stack
trace.
Closes: https://github.com/NixOS/nix/issues/7816
without this, there is no way to swap them out for structures using a
different allocator. This should be reverted as part of redesiging
ExprAttrs to use an ExprAttrsBuilder
And also render the docs nicely.
I would like to use a markdown AST for this, but to avoid new deps
(lowdown's AST doesn't suffice) I am just doing crude string
manipulations for now.
Replace the null-terminated C-style strings in Value with hybrid C /
Pascal strings, where the length is stored in the allocation before the
data, and there is still a null byte at the end for the sake of C
interopt.
Co-Authored-By: Taeer Bar-Yam <taeer@bar-yam.me>
Co-Authored-By: Sergei Zimmerman <sergei@zimmerman.foo>
These steps are done (originally in order, but I squashed it as the end
result is still pretty small, and the churn in the code comments was a
bit annoying to keep straight).
1. Create proper struct type for string contexts on the heap
This will make it easier to change this type in the future.
2. Make `Value::StringWithContext` iterable
This make some for loops a lot more terse.
3. Encapsulate `Value::StringWithContext::Context::elems`
It turns out the iterators we just exposed are sufficient.
4. Make `StringWithContext::Context` length-prefixed instead
Rather than having a null pointer at the end, have a `size_t` at the
beginning. This is the exact same size (note that null pointer is
longer than null byte) and thus takes no more space!
Also, see the new TODO on naming. The thing we already so-named is a
builder type for string contexts, not the on-heap type. The
`fromBuilder` static method reflects what the names ought to be too.
Co-authored-by: Sergei Zimmerman <sergei@zimmerman.foo>
Otherwise PosTable grows indefinitely for each reload. Since
the total input size is limited to 4GB (uint32_t for byte offset PosIdx)
it can get exhausted pretty. This ensures that we don't waste memory
on reloads as well.
It is better to avoid null termination for performance and memory
safety, wherever possible.
These are good cleanups extracted from the Pascal String work that we
can land by themselves first, shrinking the diff in that PR.
Co-Authored-By: Aspen Smith <root@gws.fyi>
Co-Authored-By: Sergei Zimmerman <sergei@zimmerman.foo>
Refactor `ExprConcatStrings::eval` by inlining two only-called-once
closures into the call-site, so that the code is easier to reason about
locally (especially since the variables that were closed over were
mutated all over the place within this function).
Also use curly braces with each branch for consistency in the the
resulting code.
This is a pure refactor, but also arguably causes us to depend less on
the optimizer; now, we don't have to make sure that this closure is
inlined.
Firstly, this is now available on darwin where the default in llvm 19.
Secondly, this leads to very weird segfaults when building with newer nixpkgs for some reason.
(It's UB after all).
This appears when building with the following:
mesonComponentOverrides = finalAttrs: prevAttrs: {
mesonBuildType = "debugoptimized";
dontStrip = true;
doCheck = false;
separateDebugInfo = false;
preConfigure = (prevAttrs.preConfigure or "") + ''
case "$mesonBuildType" in
release|minsize|debugoptimized) appendToVar mesonFlags "-Db_lto=true" ;;
*) appendToVar mesonFlags "-Db_lto=false" ;;
esac
'';
};
And with the following nixpkgs input:
nix build ".#nix-cli" -L --override-input nixpkgs "https://releases.nixos.org/nixos/unstable/nixos-25.11pre870157.7df7ff7d8e00/nixexprs.tar.xz"
Stacktrace:
#0 0x00000000006afdc0 in ?? ()
#1 0x00007ffff71cebb6 in _Unwind_ForcedUnwind_Phase2 () from /nix/store/41ym1jm1b7j3rhglk82gwg9jml26z1km-gcc-14.3.0-lib/lib/libgcc_s.so.1
#2 0x00007ffff71cf5b5 in _Unwind_Resume () from /nix/store/41ym1jm1b7j3rhglk82gwg9jml26z1km-gcc-14.3.0-lib/lib/libgcc_s.so.1
#3 0x00007ffff7eac7d8 in std::basic_ios<char, std::char_traits<char> >::~basic_ios (this=<optimized out>, this=<optimized out>)
at /nix/store/82kmz7r96navanrc2fgckh2bamiqrgsw-gcc-14.3.0/include/c++/14.3.0/bits/basic_ios.h:286
#4 std::__cxx11::basic_ostringstream<char, std::char_traits<char>, std::allocator<char> >::basic_ostringstream (this=<optimized out>, this=<optimized out>)
at /nix/store/82kmz7r96navanrc2fgckh2bamiqrgsw-gcc-14.3.0/include/c++/14.3.0/sstream:806
#5 nix::SimpleLogger::logEI (this=<optimized out>, ei=...) at ../logging.cc:121
#6 0x00007ffff7515794 in nix::Logger::logEI (this=0x675450, lvl=nix::lvlError, ei=...) at /nix/store/bkshji3nnxmrmgwa4n2kaxadajkwvn65-nix-util-2.32.0pre-dev/include/nix/util/logging.hh:144
#7 nix::handleExceptions (programName=..., fun=...) at ../shared.cc:336
#8 0x000000000047b76b in main (argc=<optimized out>, argv=<optimized out>) at /nix/store/82kmz7r96navanrc2fgckh2bamiqrgsw-gcc-14.3.0/include/c++/14.3.0/bits/new_allocator.h:88
Best I can tell this was never supposed to be exposed to the user
and has been this way since 2.19.
2.18 did not expose this file to the user:
nix run nix/2.18-maintenance -- eval --expr "import <nix/derivation-internal.nix>"
error: getting status of '/__corepkgs__/derivation-internal.nix': No such file or directory
1. Saves 24-32 bytes per string (size of std::string)
2. Saves additional bytes by not over-allocating strings (in total we
save ~1% memory)
3. Sets us up to perform a similar transformation on the other Expr
subclasses
4. Makes ExprString trivially moveable (before the string data might
move, causing the Value's pointer to become invalid). This is important
so we can put ExprStrings in an std::vector and refer to them by index
We have introduced a string copy in ParserState::stripIndentation().
This could be removed by pre-allocating the right sized string in the
arena, but this adds complexity and doesn't seem to improve performance,
so for now we've left the copy in.
fetchToStore() caching was broken because it uses the fingerprint of
the accessor, but now that the accessor (typically storeFS) is a
composite (like MountedSourceAccessor or AllowListSourceAccessor),
there was no fingerprint anymore. So fetchToStore now uses the new
getFingerprint() method to get the specific fingerprint for the
subpath.
These counters are extremely expensive in a multi-threaded
program. For instance, disabling them speeds up evaluation of the
NixOS/nix/2.21.2 from 32.6s to 17.8s.
This has multiple dangling pointer issues that lead to segfaults in e.g.:
nix eval --expr '(builtins.getFlake "github:nixos/nixpkgs/25.05")' --impure
This reverts commit ad175727e4, reversing
changes made to d314750174.
