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b13143280c
In the multithreaded evaluator, it's possible for multiple threads to wait on the same thunk. If evaluation of the thunk results in an exception, the waiting threads shouldn't try to re-force the thunk. Instead, they should rethrow the same exception, without duplicating any work. Therefore, there is now a new value type `tFailed` that stores an std::exception_ptr. If evaluation of a thunk/app results in an exception, `forceValue()` overwrites the value with a `tFailed`. If `forceValue()` encounters a `tFailed`, it rethrows the exception. So you normally never need to check for failed values (since forcing them causes a rethrow).
102 lines
3 KiB
C++
102 lines
3 KiB
C++
#include "nix/expr/print-ambiguous.hh"
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#include "nix/expr/print.hh"
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#include "nix/util/signals.hh"
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#include "nix/expr/eval.hh"
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namespace nix {
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// See: https://github.com/NixOS/nix/issues/9730
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void printAmbiguous(
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Value & v, const SymbolTable & symbols, std::ostream & str, std::set<const void *> * seen, int depth)
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{
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checkInterrupt();
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if (depth <= 0) {
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str << "«too deep»";
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return;
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}
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switch (v.type()) {
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case nInt:
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str << v.integer();
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break;
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case nBool:
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printLiteralBool(str, v.boolean());
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break;
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case nString:
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printLiteralString(str, v.string_view());
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break;
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case nPath:
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str << v.path().to_string(); // !!! escaping?
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break;
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case nNull:
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str << "null";
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break;
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case nAttrs: {
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if (seen && !v.attrs()->empty() && !seen->insert(v.attrs()).second)
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str << "«repeated»";
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else {
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str << "{ ";
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for (auto & i : v.attrs()->lexicographicOrder(symbols)) {
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str << symbols[i->name] << " = ";
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printAmbiguous(*i->value, symbols, str, seen, depth - 1);
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str << "; ";
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}
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str << "}";
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}
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break;
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}
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case nList:
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/* Use pointer to the Value instead of pointer to the elements, because
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that would need to explicitly handle the case of SmallList. */
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if (seen && v.listSize() && !seen->insert(&v).second)
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str << "«repeated»";
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else {
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str << "[ ";
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for (auto v2 : v.listView()) {
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if (v2)
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printAmbiguous(*v2, symbols, str, seen, depth - 1);
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else
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str << "(nullptr)";
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str << " ";
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}
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str << "]";
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}
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break;
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case nThunk:
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if (!v.isBlackhole()) {
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str << "<CODE>";
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} else {
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// Although we know for sure that it's going to be an infinite recursion
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// when this value is accessed _in the current context_, it's likely
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// that the user will misinterpret a simpler «infinite recursion» output
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// as a definitive statement about the value, while in fact it may be
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// a valid value after `builtins.trace` and perhaps some other steps
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// have completed.
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str << "«potential infinite recursion»";
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}
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break;
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case nFailed:
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str << "«failed»";
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break;
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case nFunction:
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if (v.isLambda()) {
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str << "<LAMBDA>";
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} else if (v.isPrimOp()) {
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str << "<PRIMOP>";
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} else if (v.isPrimOpApp()) {
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str << "<PRIMOP-APP>";
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}
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break;
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case nExternal:
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str << *v.external();
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break;
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case nFloat:
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str << v.fpoint();
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break;
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default:
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printError("Nix evaluator internal error: printAmbiguous: invalid value type");
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unreachable();
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}
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}
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} // namespace nix
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