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Merge pull request #12023 from mightyiam/head-called-on-empty-list

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Improve `builtins.{head,elemAt}` error messages
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mergify[bot] 2024-12-14 15:46:28 +00:00 • committed by GitHub
commit 44bc4c6365
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2 changed files with 26 additions and 24 deletions
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14
src/libexpr-tests/error_traces.cc
View file

@ -691,15 +691,15 @@ namespace nix {
ASSERT_TRACE2("elemAt \"foo\" (-1)",
TypeError,
HintFmt("expected a list but found %s: %s", "a string", Uncolored(ANSI_MAGENTA "\"foo\"" ANSI_NORMAL)),
HintFmt("while evaluating the first argument passed to builtins.elemAt"));
HintFmt("while evaluating the first argument passed to 'builtins.elemAt'"));
ASSERT_TRACE1("elemAt [] (-1)",
Error,
HintFmt("list index %d is out of bounds", -1));
HintFmt("'builtins.elemAt' called with index %d on a list of size %d", -1, 0));
ASSERT_TRACE1("elemAt [\"foo\"] 3",
Error,
HintFmt("list index %d is out of bounds", 3));
HintFmt("'builtins.elemAt' called with index %d on a list of size %d", 3, 1));
}
@ -708,11 +708,11 @@ namespace nix {
ASSERT_TRACE2("head 1",
TypeError,
HintFmt("expected a list but found %s: %s", "an integer", Uncolored(ANSI_CYAN "1" ANSI_NORMAL)),
HintFmt("while evaluating the first argument passed to builtins.elemAt"));
HintFmt("while evaluating the first argument passed to 'builtins.head'"));
ASSERT_TRACE1("head []",
Error,
HintFmt("list index %d is out of bounds", 0));
HintFmt("'builtins.head' called on an empty list"));
}
@ -721,11 +721,11 @@ namespace nix {
ASSERT_TRACE2("tail 1",
TypeError,
HintFmt("expected a list but found %s: %s", "an integer", Uncolored(ANSI_CYAN "1" ANSI_NORMAL)),
HintFmt("while evaluating the first argument passed to builtins.tail"));
HintFmt("while evaluating the first argument passed to 'builtins.tail'"));
ASSERT_TRACE1("tail []",
Error,
HintFmt("'tail' called on an empty list"));
HintFmt("'builtins.tail' called on an empty list"));
}

36
src/libexpr/primops.cc
View file

@ -3259,23 +3259,19 @@ static RegisterPrimOp primop_isList({
.fun = prim_isList,
});
static void elemAt(EvalState & state, const PosIdx pos, Value & list, int n, Value & v)
{
state.forceList(list, pos, "while evaluating the first argument passed to builtins.elemAt");
if (n < 0 || (unsigned int) n >= list.listSize())
state.error<EvalError>(
"list index %1% is out of bounds",
n
).atPos(pos).debugThrow();
state.forceValue(*list.listElems()[n], pos);
v = *list.listElems()[n];
}
/* Return the n-1'th element of a list. */
static void prim_elemAt(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
NixInt::Inner elem = state.forceInt(*args[1], pos, "while evaluating the second argument passed to builtins.elemAt").value;
elemAt(state, pos, *args[0], elem, v);
NixInt::Inner n = state.forceInt(*args[1], pos, "while evaluating the second argument passed to 'builtins.elemAt'").value;
state.forceList(*args[0], pos, "while evaluating the first argument passed to 'builtins.elemAt'");
if (n < 0 || (unsigned int) n >= args[0]->listSize())
state.error<EvalError>(
"'builtins.elemAt' called with index %d on a list of size %d",
n,
args[0]->listSize()
).atPos(pos).debugThrow();
state.forceValue(*args[0]->listElems()[n], pos);
v = *args[0]->listElems()[n];
}
static RegisterPrimOp primop_elemAt({
@ -3291,7 +3287,13 @@ static RegisterPrimOp primop_elemAt({
/* Return the first element of a list. */
static void prim_head(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
elemAt(state, pos, *args[0], 0, v);
state.forceList(*args[0], pos, "while evaluating the first argument passed to 'builtins.head'");
if (args[0]->listSize() == 0)
state.error<EvalError>(
"'builtins.head' called on an empty list"
).atPos(pos).debugThrow();
state.forceValue(*args[0]->listElems()[0], pos);
v = *args[0]->listElems()[0];
}
static RegisterPrimOp primop_head({
@ -3310,9 +3312,9 @@ static RegisterPrimOp primop_head({
don't want to use it! */
static void prim_tail(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
state.forceList(*args[0], pos, "while evaluating the first argument passed to builtins.tail");
state.forceList(*args[0], pos, "while evaluating the first argument passed to 'builtins.tail'");
if (args[0]->listSize() == 0)
state.error<EvalError>("'tail' called on an empty list").atPos(pos).debugThrow();
state.error<EvalError>("'builtins.tail' called on an empty list").atPos(pos).debugThrow();
auto list = state.buildList(args[0]->listSize() - 1);
for (const auto & [n, v] : enumerate(list))