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Add functionInfo builtin #8961

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46 changes: 46 additions & 0 deletions src/libexpr/primops.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2790,6 +2790,52 @@ static RegisterPrimOp primop_functionArgs({
.fun = prim_functionArgs,
});

static void prim_functionInfo(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
state.forceValue(*args[0], pos);
if (args[0]->isPrimOpApp() || args[0]->isPrimOp()) {
v.mkAttrs(&state.emptyBindings);
return;
}
if (!args[0]->isLambda())
state.debugThrowLastTrace(TypeError({
.msg = hintfmt("'functionArgs' requires a function"),
.errPos = state.positions[pos]
}));

if (!args[0]->lambda.fun->hasFormals()) {
v.mkAttrs(&state.emptyBindings);
return;
}

auto formals = state.buildBindings(args[0]->lambda.fun->formals->formals.size());
for (auto & i : args[0]->lambda.fun->formals->formals)
// !!! should optimise booleans (allocate only once)
formals.alloc(i.name, i.pos).mkBool(i.def);
Comment on lines +2812 to +2814
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@roberth roberth Sep 11, 2023

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This appears to be common with the functionArgs primop and should be factored out.

auto attrs = state.buildBindings(3);
if(args[0]->lambda.fun->arg) attrs.alloc("arg").mkString(state.symbols[args[0]->lambda.fun->arg]);
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@roberth roberth Sep 11, 2023

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I believe we should not expose this information. It is not needed, and it will introduce unnecessary coupling that users will have to be aware of when renaming what is otherwise a completely internal name.

attrs.alloc("ellipsis").mkBool(args[0]->lambda.fun->formals->ellipsis);
attrs.alloc("formals").mkAttrs(formals);
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@roberth roberth Sep 11, 2023

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I believe formals is an unfortunate name, and it has so far only been part of documentation, and not the language itself. This would be the last chance to fix that mistake.
args would match functionArgs. Will come back to this.

v.mkAttrs(attrs);
}

static RegisterPrimOp primop_functionInfo({
.name = "__functionInfo",
.args = {"f"},
.doc = R"(
Return information about the function including the following:

* arg - The name of the argument, this value is present for functions
that don't use attrset matching(i.e. `x: true`) and functions
that use an @-pattern(i.e. `{...}@argName`). Otherwise this
attr is absent.
* ellipsis - Set to true for functions of the form `{ a, b, ... }`.
* formals - Returns formal arguments, identical to
`builtins.functionArgs`.
)",
.fun = prim_functionInfo,
});

/* */
static void prim_mapAttrs(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
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49 changes: 49 additions & 0 deletions src/libexpr/tests/primops.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -232,6 +232,55 @@ namespace nix {
ASSERT_THAT(*y->value, IsTrue());
}

TEST_F(PrimOpTest, functionInfoWithEllipsisAndArg) {
auto v = eval("builtins.functionInfo ({ x, y ? 123, ...}@inputs: 1)");
ASSERT_THAT(v, IsAttrsOfSize(3));

auto arg = v.attrs->find(createSymbol("arg"));
ASSERT_NE(arg, nullptr);
ASSERT_THAT(*arg->value, IsStringEq("inputs"));

auto ellipsis = v.attrs->find(createSymbol("ellipsis"));
ASSERT_NE(ellipsis, nullptr);
ASSERT_THAT(*ellipsis->value, IsTrue());

auto formals = v.attrs->find(createSymbol("formals"));
ASSERT_NE(formals, nullptr);
ASSERT_THAT(*formals->value, IsAttrsOfSize(2));

auto x = formals->value->attrs->find(createSymbol("x"));
ASSERT_NE(x, nullptr);
ASSERT_THAT(*x->value, IsFalse());

auto y = formals->value->attrs->find(createSymbol("y"));
ASSERT_NE(y, nullptr);
ASSERT_THAT(*y->value, IsTrue());
}

TEST_F(PrimOpTest, functionInfoNoEllipsisNoArg) {
auto v = eval("builtins.functionInfo ({ x, y ? 123}: 1)");
ASSERT_THAT(v, IsAttrsOfSize(2));

auto arg = v.attrs->find(createSymbol("arg"));
ASSERT_EQ(arg, v.attrs->end());

auto ellipsis = v.attrs->find(createSymbol("ellipsis"));
ASSERT_NE(ellipsis, nullptr);
ASSERT_THAT(*ellipsis->value, IsFalse());

auto formals = v.attrs->find(createSymbol("formals"));
ASSERT_NE(formals, nullptr);
ASSERT_THAT(*formals->value, IsAttrsOfSize(2));

auto x = formals->value->attrs->find(createSymbol("x"));
ASSERT_NE(x, nullptr);
ASSERT_THAT(*x->value, IsFalse());

auto y = formals->value->attrs->find(createSymbol("y"));
ASSERT_NE(y, nullptr);
ASSERT_THAT(*y->value, IsTrue());
}

TEST_F(PrimOpTest, mapAttrs) {
auto v = eval("builtins.mapAttrs (name: value: value * 10) { a = 1; b = 2; }");
ASSERT_THAT(v, IsAttrsOfSize(2));
Expand Down