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nix eval: Add --apply flag for post-processing the result

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This commit is contained in:
Eelco Dolstra 2020-06-17 18:11:53 +02:00
parent 5332c439d0
commit 2e4bd78211
1 changed files with 27 additions and 7 deletions
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34
src/nix/eval.cc
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@ -12,10 +12,18 @@ using namespace nix;
struct CmdEval : MixJSON, InstallableCommand
{
bool raw = false;
std::optional<std::string> apply;
CmdEval()
{
mkFlag(0, "raw", "print strings unquoted", &raw);
addFlag({
.longName = "apply",
.description = "apply a function to each argument",
.labels = {"expr"},
.handler = {&apply},
});
}
std::string description() override
@ -26,21 +34,25 @@ struct CmdEval : MixJSON, InstallableCommand
Examples examples() override
{
return {
Example{
{
"To evaluate a Nix expression given on the command line:",
"nix eval --expr '1 + 2'"
},
Example{
{
"To evaluate a Nix expression from a file or URI:",
"nix eval -f channel:nixos-17.09 hello.name"
"nix eval -f ./my-nixpkgs hello.name"
},
Example{
{
"To get the current version of Nixpkgs:",
"nix eval --raw nixpkgs.lib.version"
"nix eval --raw nixpkgs#lib.version"
},
Example{
{
"To print the store path of the Hello package:",
"nix eval --raw nixpkgs.hello"
"nix eval --raw nixpkgs#hello"
},
{
"To get a list of checks in the 'nix' flake:",
"nix eval nix#checks.x86_64-linux --apply builtins.attrNames"
},
};
}
@ -57,6 +69,14 @@ struct CmdEval : MixJSON, InstallableCommand
auto v = installable->toValue(*state).first;
PathSet context;
if (apply) {
auto vApply = state->allocValue();
state->eval(state->parseExprFromString(*apply, absPath(".")), *vApply);
auto vRes = state->allocValue();
state->callFunction(*vApply, *v, *vRes, noPos);
v = vRes;
}
if (raw) {
stopProgressBar();
std::cout << state->coerceToString(noPos, *v, context);