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Move import docs

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Eelco Dolstra 2020-08-25 14:06:01 +02:00
parent f53b5f1058
commit 7a02865b94
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3 changed files with 80 additions and 78 deletions
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53
doc/manual/src/expressions/builtins-prefix.md
View file

@ -13,56 +13,3 @@ For instance, `derivation` is also available as `builtins.derivation`.
`derivation` is described in [its own section](derivations.md).
- `import` *path*; `builtins.import` *path*
Load, parse and return the Nix expression in the file *path*. If
*path* is a directory, the file ` default.nix ` in that directory
is loaded. Evaluation aborts if the file doesn’t exist or contains
an incorrect Nix expression. `import` implements Nix’s module
system: you can put any Nix expression (such as a set or a
function) in a separate file, and use it from Nix expressions in
other files.
> **Note**
>
> Unlike some languages, `import` is a regular function in Nix.
> Paths using the angle bracket syntax (e.g., `import` *\<foo\>*)
> are [normal path values](language-values.md).
A Nix expression loaded by `import` must not contain any *free
variables* (identifiers that are not defined in the Nix expression
itself and are not built-in). Therefore, it cannot refer to
variables that are in scope at the call site. For instance, if you
have a calling expression
```nix
rec {
x = 123;
y = import ./foo.nix;
}
```
then the following `foo.nix` will give an error:
```nix
x + 456
```
since `x` is not in scope in `foo.nix`. If you want `x` to be
available in `foo.nix`, you should pass it as a function argument:
```nix
rec {
x = 123;
y = import ./foo.nix x;
}
```
and
```nix
x: x + 456
```
(The function argument doesn’t have to be called `x` in `foo.nix`;
any name would work.)

93
src/libexpr/primops.cc
View file

@ -74,10 +74,10 @@ void EvalState::realiseContext(const PathSet & context)
/* Load and evaluate an expression from path specified by the
argument. */
static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args, Value & v)
static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vScope, Value & v)
{
PathSet context;
Path path = state.coerceToPath(pos, *args[1], context);
Path path = state.coerceToPath(pos, vPath, context);
try {
state.realiseContext(context);
@ -99,6 +99,7 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
return std::nullopt;
return storePath;
};
if (auto optStorePath = isValidDerivationInStore()) {
auto storePath = *optStorePath;
Derivation drv = readDerivation(*state.store, realPath, Derivation::nameFromPath(storePath));
@ -133,17 +134,18 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
mkApp(v, **fun, w);
state.forceAttrs(v, pos);
} else {
state.forceAttrs(*args[0]);
if (args[0]->attrs->empty())
if (!vScope)
state.evalFile(realPath, v);
else {
Env * env = &state.allocEnv(args[0]->attrs->size());
state.forceAttrs(*vScope);
Env * env = &state.allocEnv(vScope->attrs->size());
env->up = &state.baseEnv;
StaticEnv staticEnv(false, &state.staticBaseEnv);
unsigned int displ = 0;
for (auto & attr : *args[0]->attrs) {
for (auto & attr : *vScope->attrs) {
staticEnv.vars[attr.name] = displ;
env->values[displ++] = attr.value;
}
@ -156,6 +158,77 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
}
}
static RegisterPrimOp primop_scopedImport(RegisterPrimOp::Info {
.name = "scopedImport",
.arity = 2,
.fun = [](EvalState & state, const Pos & pos, Value * * args, Value & v)
{
import(state, pos, *args[1], args[0], v);
}
});
static RegisterPrimOp primop_import({
.name = "import",
.args = {"path"},
.doc = R"(
Load, parse and return the Nix expression in the file *path*. If
*path* is a directory, the file ` default.nix ` in that directory
is loaded. Evaluation aborts if the file doesn’t exist or contains
an incorrect Nix expression. `import` implements Nix’s module
system: you can put any Nix expression (such as a set or a
function) in a separate file, and use it from Nix expressions in
other files.
> **Note**
>
> Unlike some languages, `import` is a regular function in Nix.
> Paths using the angle bracket syntax (e.g., `import` *\<foo\>*)
> are [normal path values](language-values.md).
A Nix expression loaded by `import` must not contain any *free
variables* (identifiers that are not defined in the Nix expression
itself and are not built-in). Therefore, it cannot refer to
variables that are in scope at the call site. For instance, if you
have a calling expression
```nix
rec {
x = 123;
y = import ./foo.nix;
}
```
then the following `foo.nix` will give an error:
```nix
x + 456
```
since `x` is not in scope in `foo.nix`. If you want `x` to be
available in `foo.nix`, you should pass it as a function argument:
```nix
rec {
x = 123;
y = import ./foo.nix x;
}
```
and
```nix
x: x + 456
```
(The function argument doesn’t have to be called `x` in `foo.nix`;
any name would work.)
)",
.fun = [](EvalState & state, const Pos & pos, Value * * args, Value & v)
{
import(state, pos, *args[0], nullptr, v);
}
});
/* Want reasonable symbol names, so extern C */
/* !!! Should we pass the Pos or the file name too? */
extern "C" typedef void (*ValueInitializer)(EvalState & state, Value & v);
@ -3429,12 +3502,6 @@ void EvalState::createBaseEnv()
addConstant("__langVersion", v);
// Miscellaneous
auto vScopedImport = addPrimOp("scopedImport", 2, prim_scopedImport);
Value * v2 = allocValue();
mkAttrs(*v2, 0);
mkApp(v, *vScopedImport, *v2);
forceValue(v);
addConstant("import", v);
if (evalSettings.enableNativeCode) {
addPrimOp("__importNative", 2, prim_importNative);
addPrimOp("__exec", 1, prim_exec);
@ -3444,7 +3511,7 @@ void EvalState::createBaseEnv()
mkList(v, searchPath.size());
int n = 0;
for (auto & i : searchPath) {
v2 = v.listElems()[n++] = allocValue();
auto v2 = v.listElems()[n++] = allocValue();
mkAttrs(*v2, 2);
mkString(*allocAttr(*v2, symbols.create("path")), i.second);
mkString(*allocAttr(*v2, symbols.create("prefix")), i.first);

12
tests/function-trace.sh
View file

@ -32,8 +32,6 @@ expect_trace() {
# failure inside a tryEval
expect_trace 'builtins.tryEval (throw "example")' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace entered (string):1:19 at
function-trace exited (string):1:19 at
@ -42,32 +40,24 @@ function-trace exited (string):1:1 at
# Missing argument to a formal function
expect_trace '({ x }: x) { }' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace exited (string):1:1 at
"
# Too many arguments to a formal function
expect_trace '({ x }: x) { x = "x"; y = "y"; }' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace exited (string):1:1 at
"
# Not enough arguments to a lambda
expect_trace '(x: y: x + y) 1' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace exited (string):1:1 at
"
# Too many arguments to a lambda
expect_trace '(x: x) 1 2' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace exited (string):1:1 at
function-trace entered (string):1:1 at
@ -76,8 +66,6 @@ function-trace exited (string):1:1 at
# Not a function
expect_trace '1 2' "
function-trace entered undefined position at
function-trace exited undefined position at
function-trace entered (string):1:1 at
function-trace exited (string):1:1 at
"