nixos/nix
1
1
Fork 0
mirror of https://github.com/NixOS/nix.git synced 2025-11-12 13:36:02 +01:00
Code Activity

Encapsulate and slightly optimize string contexts

Browse source 
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>
This commit is contained in:
John Ericson 2025-11-03 18:53:27 -05:00 • committed by Sergei Zimmerman
parent 6ebaba50dd
commit 318eea040f
No known key found for this signature in database
4 changed files with 97 additions and 23 deletions
Download patch file Download diff file Expand all files Collapse all files

32
src/libexpr/eval.cc
View file

@ -36,6 +36,7 @@
#include <sys/time.h>
#include <fstream>
#include <functional>
#include <ranges>
#include <nlohmann/json.hpp>
#include <boost/container/small_vector.hpp>
@ -821,28 +822,25 @@ void Value::mkString(std::string_view s)
mkStringNoCopy(makeImmutableString(s));
}
static const char ** encodeContext(const NixStringContext & context)
Value::StringWithContext::Context * Value::StringWithContext::Context::fromBuilder(const NixStringContext & context)
{
if (!context.empty()) {
size_t n = 0;
auto ctx = (const char **) allocBytes((context.size() + 1) * sizeof(char *));
for (auto & i : context) {
ctx[n++] = makeImmutableString({i.to_string()});
}
ctx[n] = nullptr;
return ctx;
} else
if (context.empty())
return nullptr;
auto ctx = new (allocBytes(sizeof(Context) + context.size() * sizeof(value_type))) Context(context.size());
std::ranges::transform(
context, ctx->elems, [](const NixStringContextElem & elt) { return makeImmutableString(elt.to_string()); });
return ctx;
}
void Value::mkString(std::string_view s, const NixStringContext & context)
{
mkStringNoCopy(makeImmutableString(s), encodeContext(context));
mkStringNoCopy(makeImmutableString(s), Value::StringWithContext::Context::fromBuilder(context));
}
void Value::mkStringMove(const char * s, const NixStringContext & context)
{
mkStringNoCopy(s, encodeContext(context));
mkStringNoCopy(s, Value::StringWithContext::Context::fromBuilder(context));
}
void Value::mkPath(const SourcePath & path)
@ -2287,9 +2285,9 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
void copyContext(const Value & v, NixStringContext & context, const ExperimentalFeatureSettings & xpSettings)
{
if (v.context())
for (const char ** p = v.context(); *p; ++p)
context.insert(NixStringContextElem::parse(*p, xpSettings));
if (auto * ctx = v.context())
for (auto * elem : *ctx)
context.insert(NixStringContextElem::parse(elem, xpSettings));
}
std::string_view EvalState::forceString(
@ -2309,7 +2307,9 @@ std::string_view EvalState::forceStringNoCtx(Value & v, const PosIdx pos, std::s
auto s = forceString(v, pos, errorCtx);
if (v.context()) {
error<EvalError>(
"the string '%1%' is not allowed to refer to a store path (such as '%2%')", v.string_view(), v.context()[0])
"the string '%1%' is not allowed to refer to a store path (such as '%2%')",
v.string_view(),
*v.context()->begin())
.withTrace(pos, errorCtx)
.debugThrow();
}