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libexpr: significantly improve error messages for bad attr paths

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This commit makes Lix include the summarized content of the value being
indexed when it is bad.

lix/lix2 » nix eval --expr '{x.y = 2;}' 'x.y.z'
error: the value being indexed in the selection path 'x.y.z' at 'x.y' should be a set but is an integer: 2

lix/lix2 » nix eval --expr '{x.y = { a = 3; };}' 'x.y.z'
error: attribute 'z' in selection path 'x.y.z' not found inside path 'x.y', whose contents are: { a = 3; }
       Did you mean a?

lix/lix2 » nix eval --expr '{x.y = { a = 3; };}' 'x.y.1'
error: the expression selected by the selection path 'x.y.1' should be a list but is a set: { a = 3; }

Change-Id: I3202aba0e437e00b4c6d3ee287a2d9a7c6892dbf
This commit is contained in:
jade 2024-12-05 14:34:38 -08:00
parent c0808bd855
commit faf00ad022
5 changed files with 125 additions and 25 deletions
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25
doc/manual/rl-next/better-errors-attrpaths.md Normal file
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@ -0,0 +1,25 @@
---
synopsis: "Improved error messages for bad attr paths"
category: Improvements
cls: [2277, 2280]
credits: jade
---
Lix now includes much more detail when a bad attribute path is accessed at the command line:
```
» nix eval -f '<nixpkgs>' lixVersions.lix_2_92
error: attribute 'lix_2_92' in selection path 'lixVersions.lix_2_92' not found
Did you mean one of lix_2_90 or lix_2_91?
```
After:
```
» nix eval --impure -f '<nixpkgs>' lixVersions.lix_2_92
error: attribute 'lix_2_92' in selection path 'lixVersions.lix_2_92' not found inside path 'lixVersions', whose contents are: { __unfix__ = «lambda @ /nix/store/hfz1qqd0z8amlgn8qwich1dvkmldik36-source/lib/fixed-points.nix:
447:7»; buildLix = «thunk»; extend = «thunk»; latest = «thunk»; lix_2_90 = «thunk»; lix_2_91 = «thunk»; override = «thunk»; overrideDerivation = «thunk»; recurseForDerivations = true; stable = «thunk»; }
Did you mean one of lix_2_90 or lix_2_91?
```
This should avoid some unnecessary trips to the repl or to the debugger by giving some information about the value being selected on that was unexpected.

56
lix/libexpr/attr-path.cc
View file

@ -1,5 +1,6 @@
#include "lix/libexpr/attr-path.hh"
#include "lix/libexpr/eval-inline.hh"
#include "print-options.hh"
#include <algorithm>
#include <sstream>
@ -96,12 +97,18 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
throw Error("empty attribute name in selection path '%1%'", attrPath);
if (v->type() != nAttrs) {
auto pathPart = std::vector<std::string>(tokens.begin(), tokens.begin() + attrPathIdx);
state.ctx.errors.make<TypeError>(
"the value being indexed in the selection path '%1%' at '%2%' should be a set but is %3%",
auto pathPart =
std::vector<std::string>(tokens.begin(), tokens.begin() + attrPathIdx);
state.ctx.errors
.make<TypeError>(
"the value being indexed in the selection path '%1%' at '%2%' should be a "
"set but is %3%: %4%",
attrPath,
unparseAttrPath(pathPart),
showType(*v)).debugThrow();
showType(*v),
ValuePrinter(state, *v, errorPrintOptions)
)
.debugThrow();
}
Bindings::iterator a = v->attrs->find(state.ctx.symbols.create(attr));
@ -111,21 +118,40 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
attrNames.insert(state.ctx.symbols[attr.name]);
auto suggestions = Suggestions::bestMatches(attrNames, attr);
throw AttrPathNotFound(suggestions, "attribute '%1%' in selection path '%2%' not found", attr, attrPath);
auto pathPart =
std::vector<std::string>(tokens.begin(), tokens.begin() + attrPathIdx);
throw AttrPathNotFound(
suggestions,
"attribute '%1%' in selection path '%2%' not found inside path '%3%', whose "
"contents are: %4%",
attr,
attrPath,
unparseAttrPath(pathPart),
ValuePrinter(state, *v, errorPrintOptions)
);
}
v = &*a->value;
pos = a->pos;
}
else {
if (!v->isList())
state.ctx.errors.make<TypeError>(
"the expression selected by the selection path '%1%' should be a list but is %2%",
} else {
if (!v->isList()) {
state.ctx.errors
.make<TypeError>(
"the expression selected by the selection path '%1%' should be a list but "
"is %2%: %3%",
attrPath,
showType(*v)).debugThrow();
if (*attrIndex >= v->listSize())
throw AttrPathNotFound("list index %1% in selection path '%2%' is out of range", *attrIndex, attrPath);
showType(*v),
ValuePrinter(state, *v, errorPrintOptions)
)
.debugThrow();
}
if (*attrIndex >= v->listSize()) {
throw AttrPathNotFound(
"list index %1% in selection path '%2%' is out of range for list %3%",
*attrIndex,
attrPath,
ValuePrinter(state, *v, errorPrintOptions)
);
}
v = v->listElems()[*attrIndex];
pos = noPos;

7
tests/functional/misc.sh
View file

@ -24,13 +24,6 @@ eval_stdin_res=$(echo 'let a = {} // a; in a.foo' | nix-instantiate --eval -E -
echo $eval_stdin_res | grep "at «stdin»:1:15:"
echo $eval_stdin_res | grep "infinite recursion encountered"
# Attribute path errors
expectStderr 1 nix-instantiate --eval -E '{}' -A '"x' | grepQuiet "missing closing quote in selection path"
expectStderr 1 nix-instantiate --eval -E '[]' -A 'x' | grepQuiet "should be a set"
expectStderr 1 nix-instantiate --eval -E '{}' -A '1' | grepQuiet "should be a list"
expectStderr 1 nix-instantiate --eval -E '{}' -A '.' | grepQuiet "empty attribute name"
expectStderr 1 nix-instantiate --eval -E '[]' -A '1' | grepQuiet "out of range"
# Unknown setting warning
# NOTE(cole-h): behavior is different depending on the order, which is why we test an unknown option
# before and after the `'{}'`!

56
tests/functional2/eval/test_attr_paths.py Normal file
View file

@ -0,0 +1,56 @@
from functional2.testlib.fixtures import Nix
import pytest
from typing import NamedTuple
from textwrap import dedent
class ShouldError(NamedTuple):
expr: str
attr: str
error: str
ERR_CASES: list[ShouldError] = [
# FIXME(jade): expect-test system for pytest that allows for updating these easily
ShouldError('{}', '"x',
"""error: missing closing quote in selection path '"x'"""),
ShouldError(
'[]', 'x',
"""error: the value being indexed in the selection path 'x' at '' should be a set but is a list: [ ]"""
),
ShouldError(
'{}', '1',
"""error: the expression selected by the selection path '1' should be a list but is a set: { }"""
),
ShouldError('{}', '.',
"""error: empty attribute name in selection path '.'"""),
ShouldError('{ x."" = 2; }', 'x.""',
"""error: empty attribute name in selection path 'x.""'"""),
ShouldError('{ x."".y = 2; }', 'x."".y',
"""error: empty attribute name in selection path 'x."".y'"""),
ShouldError(
'[]', '1',
"""error: list index 1 in selection path '1' is out of range for list [ ]"""
),
ShouldError(
'{ x.y = { z = 2; a = 3; }; }', 'x.y.c',
dedent("""\
error: attribute 'c' in selection path 'x.y.c' not found inside path 'x.y', whose contents are: { a = 3; z = 2; }
Did you mean one of a or z?""")
),
]
# I do not know why it does this, but I guess it makes sense as allowing a tool
# to pass -A unconditionally and then allow a blank attribute to mean the whole
# thing
def test_attrpath_accepts_empty_attr_as_no_attr(nix: Nix):
assert nix.nix_instantiate(['--eval', '--expr', '{}', '-A',
'']).run().ok().stdout_plain == '{ }'
@pytest.mark.parametrize(['expr', 'attr', 'error'], ERR_CASES)
def test_attrpath_error(nix: Nix, expr: str, attr: str, error: str):
res = nix.nix_instantiate(['--eval', '--expr', expr, '-A', attr]).run()
assert res.expect(1).stderr_plain == error

2
tests/functional2/test_eval_trivial.py → tests/functional2/eval/test_eval_trivial.py
View file

@ -1,4 +1,4 @@
from .testlib.fixtures import Nix
from functional2.testlib.fixtures import Nix
def test_trivial_addition(nix: Nix):
assert nix.eval('1 + 1').json() == 2