Commit graph

22 commits

Author SHA1 Message Date
Eelco Dolstra fab731a9d4 Don't pass Symbol by reference
Since Symbol is just an integer, passing it by const reference is
never advantageous.
2022-04-26 13:25:17 +02:00
pennae a385e51a08 rename SymbolIdx -> Symbol, Symbol -> SymbolStr
after #6218 `Symbol` no longer confers a uniqueness invariant on the
string it wraps, it is now possible to create multiple symbols that
compare equal but whose string contents have different addresses. this
guarantee is now only provided by `SymbolIdx`, leaving `Symbol` only as
a string wrapper that knows about the intricacies of how symbols need to
be formatted for output.

this change renames `SymbolIdx` to `Symbol` to restore the previous
semantics of `Symbol` to that name. we also keep the wrapper type and
rename it to `SymbolStr` instead of returning plain strings from lookups
into the symbol table because symbols are formatted for output in many
places. theoretically we do not need `SymbolStr`, only a function that
formats a string for output as a symbol, but having to wrap every symbol
that appears in a message into eg `formatSymbol()` is error-prone and
inconvient.
2022-04-25 15:37:01 +02:00
pennae 8168a4cf4a shrink Attr by 8 bytes on 64bit machines
with position and symbol tables in place we can now shrink Attr by a full
pointer with some simple field reordering. since Attr is a very hot struct this
has substantial impact on memory use, decreasing GC allocations and heap size by
10-15% each. we also get a ~15% performance improvement due to reduced GC
loading.

pure parsing has taken a hit over the branch base because positions are now
slightly more expensive to create, but overall we get a noticeable improvement.

before (on memory-friendliness):

  Benchmark 1: nix search --no-eval-cache --offline ../nixpkgs hello
    Time (mean ± σ):      6.960 s ±  0.028 s    [User: 5.832 s, System: 0.897 s]
    Range (min … max):    6.886 s …  7.005 s    20 runs

  Benchmark 2: nix eval -f ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
    Time (mean ± σ):     328.1 ms ±   1.7 ms    [User: 295.8 ms, System: 32.2 ms]
    Range (min … max):   324.9 ms … 331.2 ms    20 runs

  Benchmark 3: nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
    Time (mean ± σ):      2.688 s ±  0.029 s    [User: 2.365 s, System: 0.238 s]
    Range (min … max):    2.642 s …  2.742 s    20 runs

after:

  Benchmark 1: nix search --no-eval-cache --offline ../nixpkgs hello
    Time (mean ± σ):      6.902 s ±  0.039 s    [User: 5.844 s, System: 0.783 s]
    Range (min … max):    6.820 s …  6.956 s    20 runs

  Benchmark 2: nix eval -f ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
    Time (mean ± σ):     330.7 ms ±   2.2 ms    [User: 300.6 ms, System: 30.0 ms]
    Range (min … max):   327.5 ms … 334.5 ms    20 runs

  Benchmark 3: nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
    Time (mean ± σ):      2.330 s ±  0.027 s    [User: 2.040 s, System: 0.234 s]
    Range (min … max):    2.272 s …  2.383 s    20 runs
2022-04-21 21:56:34 +02:00
pennae 8775be3393 store Symbols in a table as well, like positions
this slightly increases the amount of memory used for any given symbol, but this
increase is more than made up for if the symbol is referenced more than once in
the EvalState that holds it. on average every symbol should be referenced at
least twice (once to introduce a binding, once to use it), so we expect no
increase in memory on average.

symbol tables are limited to 2³² entries like position tables, and similar
arguments apply to why overflow is not likely: 2³² symbols would require as many
string instances (at 24 bytes each) and map entries (at 24 bytes or more each,
assuming that the map holds on average at most one item per bucket as the docs
say). a full symbol table would require at least 192GB of memory just for
symbols, which is well out of reach. (an ofborg eval of nixpks today creates
less than a million symbols!)
2022-04-21 21:56:31 +02:00
pennae 6526d1676b replace most Pos objects/ptrs with indexes into a position table
Pos objects are somewhat wasteful as they duplicate the origin file name and
input type for each object. on files that produce more than one Pos when parsed
this a sizeable waste of memory (one pointer per Pos). the same goes for
ptr<Pos> on 64 bit machines: parsing enough source to require 8 bytes to locate
a position would need at least 8GB of input and 64GB of expression memory. it's
not likely that we'll hit that any time soon, so we can use a uint32_t index to
locate positions instead.
2022-04-21 21:46:06 +02:00
pennae 38de79fcf7 remove Bindings::need
a future commit will remove the ability to convert the symbol type used in
bindings to strings. since we only have two users we can inline the error check.
2022-04-21 21:25:18 +02:00
Eelco Dolstra df552ff53e Remove std::string alias (for real this time)
Also use std::string_view in a few more places.
2022-02-25 16:13:02 +01:00
pennae c9fc975259 optimize removeAttrs builtin
use a sorted array of symbols to be removed instead of a set. this saves a lot
of memory allocations and slightly speeds up removal.
2022-01-14 14:01:52 +01:00
Eelco Dolstra 2b4c944823 Remove EvalState::mkAttrs() 2022-01-04 20:29:17 +01:00
Eelco Dolstra 6d9a6d2cc3 Ensure that attrsets are sorted
Previously you had to remember to call value->attrs->sort() after
populating value->attrs. Now there is a BindingsBuilder helper that
wraps Bindings and ensures that sort() is called before you can use
it.
2022-01-04 18:00:33 +01:00
Robert Hensing f10465774f Force all Pos* to be non-null
This fixes a class of crashes and introduces ptr<T> to make the
code robust against this failure mode going forward.

Thanks regnat for the idea of a ref<T> without overhead!

Closes #4895
Closes #4893
Closes #5127
Closes #5113
2021-08-29 18:11:58 +02:00
Maximilian Bosch 7c76964daa
libexpr: misc improvements for proper error position
When working on some more complex Nix code, there are sometimes rather
unhelpful or misleading error messages, especially if coerce-errors are
thrown.

This patch is a first steps towards improving that. I'm happy to file
more changes after that, but I'd like to gather some feedback first.

To summarize, this patch does the following things:

* Attrsets (a.k.a. `Bindings` in `libexpr`) now have a `Pos`. This is
  helpful e.g. to identify which attribute-set in `listToAttrs` is
  invalid.

* The `Value`-struct has a new method named `determinePos` which tries
  to guess the position of a value and falls back to a default if that's
  not possible.

  This can be used to provide better messages if a coercion fails.

* The new `determinePos`-API is used by `builtins.concatMap` now. With
  that change, Nix shows the exact position in the error where a wrong
  value was returned by the lambda.

  To make sure it's still obvious that `concatMap` is the problem,
  another stack-frame was added.

* The changes described above can be added to every other `primop`, but
  first I'd like to get some feedback about the overall approach.
2021-04-13 23:12:38 +02:00
Eelco Dolstra 8d4268d190 Improve error formatting
Changes:

* The divider lines are gone. These were in practice a bit confusing,
  in particular with --show-trace or --keep-going, since then there
  were multiple lines, suggesting a start/end which wasn't the case.

* Instead, multi-line error messages are now indented to align with
  the prefix (e.g. "error: ").

* The 'description' field is gone since we weren't really using it.

* 'hint' is renamed to 'msg' since it really wasn't a hint.

* The error is now printed *before* the location info.

* The 'name' field is no longer printed since most of the time it
  wasn't very useful since it was just the name of the exception (like
  EvalError). Ideally in the future this would be a unique, easily
  googleable error ID (like rustc).

* "trace:" is now just "…". This assumes error contexts start with
  something like "while doing X".

Example before:

  error: --- AssertionError ---------------------------------------------------------------------------------------- nix
  at: (7:7) in file: /home/eelco/Dev/nixpkgs/pkgs/applications/misc/hello/default.nix

       6|
       7|   x = assert false; 1;
        |       ^
       8|

  assertion 'false' failed
  ----------------------------------------------------- show-trace -----------------------------------------------------
  trace: while evaluating the attribute 'x' of the derivation 'hello-2.10'
  at: (192:11) in file: /home/eelco/Dev/nixpkgs/pkgs/stdenv/generic/make-derivation.nix

     191|         // (lib.optionalAttrs (!(attrs ? name) && attrs ? pname && attrs ? version)) {
     192|           name = "${attrs.pname}-${attrs.version}";
        |           ^
     193|         } // (lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix && (attrs ? name || (attrs ? pname && attrs ? version)))) {

Example after:

  error: assertion 'false' failed

         at: (7:7) in file: /home/eelco/Dev/nixpkgs/pkgs/applications/misc/hello/default.nix

              6|
              7|   x = assert false; 1;
               |       ^
              8|

         … while evaluating the attribute 'x' of the derivation 'hello-2.10'

         at: (192:11) in file: /home/eelco/Dev/nixpkgs/pkgs/stdenv/generic/make-derivation.nix

            191|         // (lib.optionalAttrs (!(attrs ? name) && attrs ? pname && attrs ? version)) {
            192|           name = "${attrs.pname}-${attrs.version}";
               |           ^
            193|         } // (lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix && (attrs ? name || (attrs ? pname && attrs ? version)))) {
2021-01-21 11:02:09 +01:00
Ben Burdette 1d43a6e123 use plain errPos instead of nixCode; fix tests 2020-06-23 15:30:13 -06:00
Eelco Dolstra 1fb762d11f Get rid of explicit ErrorInfo constructors 2020-06-15 14:06:58 +02:00
Ben Burdette 55eb717148 add pos to errorinfo, remove from hints 2020-05-08 18:18:28 -06:00
Eelco Dolstra 9af10b753c Bindings::get(): std::optional<Attr *> -> Attr *
Returning a nullable type in an optional is silly.
2020-02-13 17:15:05 +01:00
Eelco Dolstra 79142cbbe1 Bindings: Add convenience method for requiring an attribute
(cherry picked from commit fb692e5f7b)
2019-12-05 20:29:15 +01:00
Eelco Dolstra 0d118ef0c9 Bindings::get(): Add convenience method
This allows writing attribute lookups as

    if (auto name = value.attrs->get(state.sName))
      ...

(cherry picked from commit f216c76c56)
2019-12-05 20:29:00 +01:00
Tuomas Tynkkynen 056d28a601 libexpr: Don't create lots of temporary strings in Bindings::lexicographicOrder
Avoids ~180,000 string temporaries created when evaluating a headless
NixOS system.
2018-02-19 22:47:25 +02:00
Eelco Dolstra 54801ed6ad
Bindings: Add a method for iterating in lexicographically sorted order 2017-01-26 20:40:33 +01:00
Nicolas B. Pierron db21cfa688 Move attribute set data structures into their own header file.
This modification moves Attr and Bindings structures into their own header
file which is dedicated to the attribute set representation. The goal of to
isolate pieces of code which are related to the attribute set
representation. Thus future modifications of the attribute set
representation will only have to modify these files, and not every other
file across the evaluator.
2015-07-14 19:23:17 +02:00