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WIP: Add nix repl :probe

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For checking laziness (to a degree)
This commit is contained in:
Robert Hensing 2025-03-09 15:37:39 +01:00
parent a047dec120
commit fd9ad915f6
1 changed files with 59 additions and 0 deletions
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59
src/libcmd/repl.cc
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@ -3,6 +3,7 @@
#include <cstring>
#include "error.hh"
#include "eval-error.hh"
#include "repl-interacter.hh"
#include "repl.hh"
@ -344,6 +345,58 @@ void NixRepl::loadDebugTraceEnv(DebugTrace & dt)
}
}
static Value * lazyProbe(Expr * e, EvalState &state, Env &env)
{
if (auto select = dynamic_cast<ExprSelect *>(e)) {
if (select->attrPath.size() != 1) {
throw Unsupported(":probe: Nested attribute selection not supported yet. Workaround: use parentheses?");
}
if (select->def) {
// This seems like nonsensical input, and we only really support simple attribute paths
throw Unsupported(":probe: %1% keyword is not supported.", "or");
}
auto attr = select->attrPath[0];
if (!attr.symbol) {
throw Unsupported(":probe: Computed attribute selection not supported yet.");
}
auto name = state.symbols[attr.symbol];
auto v = lazyProbe(select->e, state, env);
if (v->type() != nAttrs) {
state.error<TypeError>("can't look up '%1%', expecting the left hand side to be an attribute set, but it is %2%", name, v->type()).atPos(select->e->getPos()).debugThrow();
}
auto it = v->attrs()->find(attr.symbol);
if (it == v->attrs()->end()) {
state.error<EvalError>("attribute '%1%' missing", state.symbols[attr.symbol]).atPos(select->e->getPos()).debugThrow();
}
return it->value;
}
if (auto ref = dynamic_cast<ExprVar *>(e)) {
auto name = state.symbols[ref->name];
// TODO: subtly different intent, so factor out common logic from maybeThunk instead
Value * v = ref->maybeThunk(state, env);
if (!v) {
state.error<EvalError>("Variable '%1%' not found in scope", name).atPos(ref->getPos()).debugThrow();
}
return v;
}
state.error<EvalError>("'%s' is not an expression I can probe. Use variables and attribute selection").atPos(e->getPos()).debugThrow();
}
static void printLazyProbe(Expr * e, EvalState &state, Env &env)
{
Value * v = lazyProbe(e, state, env);
auto suspension = logger->suspend();
std::cout << (v->type() == nThunk ? ANSI_GREEN : ANSI_BLUE);
std::cout << v->type() << std::endl;
std::cout << ANSI_NORMAL;
}
ProcessLineResult NixRepl::processLine(std::string line)
{
line = trim(line);
@ -380,6 +433,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
<< " :lf, :load-flake <ref> Load Nix flake and add it to scope\n"
<< " :p, :print <expr> Evaluate and print expression recursively\n"
<< " Strings are printed directly, without escaping.\n"
<< " :probe <select> Do not evaluate, but report type or thunk.\n"
<< " :q, :quit Exit nix-repl\n"
<< " :r, :reload Reload all files\n"
<< " :sh <expr> Build dependencies of derivation, then start\n"
@ -596,6 +650,11 @@ ProcessLineResult NixRepl::processLine(std::string line)
std::cout << std::endl;
}
else if (command == ":probe") {
auto expr = parseString(arg);
printLazyProbe(expr, *state, *env);
}
else if (command == ":q" || command == ":quit") {
state->debugStop = false;
return ProcessLineResult::Quit;