7c76964daa
When working on some more complex Nix code, there are sometimes rather unhelpful or misleading error messages, especially if coerce-errors are thrown. This patch is a first steps towards improving that. I'm happy to file more changes after that, but I'd like to gather some feedback first. To summarize, this patch does the following things: * Attrsets (a.k.a. `Bindings` in `libexpr`) now have a `Pos`. This is helpful e.g. to identify which attribute-set in `listToAttrs` is invalid. * The `Value`-struct has a new method named `determinePos` which tries to guess the position of a value and falls back to a default if that's not possible. This can be used to provide better messages if a coercion fails. * The new `determinePos`-API is used by `builtins.concatMap` now. With that change, Nix shows the exact position in the error where a wrong value was returned by the lambda. To make sure it's still obvious that `concatMap` is the problem, another stack-frame was added. * The changes described above can be added to every other `primop`, but first I'd like to get some feedback about the overall approach.
118 lines
2.6 KiB
C++
118 lines
2.6 KiB
C++
#pragma once
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#include "nixexpr.hh"
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#include "symbol-table.hh"
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#include <algorithm>
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#include <optional>
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namespace nix {
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class EvalState;
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struct Value;
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/* Map one attribute name to its value. */
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struct Attr
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{
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Symbol name;
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Value * value;
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Pos * pos;
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Attr(Symbol name, Value * value, Pos * pos = &noPos)
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: name(name), value(value), pos(pos) { };
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Attr() : pos(&noPos) { };
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bool operator < (const Attr & a) const
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{
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return name < a.name;
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}
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};
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/* Bindings contains all the attributes of an attribute set. It is defined
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by its size and its capacity, the capacity being the number of Attr
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elements allocated after this structure, while the size corresponds to
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the number of elements already inserted in this structure. */
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class Bindings
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{
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public:
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typedef uint32_t size_t;
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Pos *pos;
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private:
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size_t size_, capacity_;
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Attr attrs[0];
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Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
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Bindings(const Bindings & bindings) = delete;
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public:
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size_t size() const { return size_; }
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bool empty() const { return !size_; }
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typedef Attr * iterator;
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void push_back(const Attr & attr)
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{
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assert(size_ < capacity_);
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attrs[size_++] = attr;
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}
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iterator find(const Symbol & name)
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{
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Attr key(name, 0);
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iterator i = std::lower_bound(begin(), end(), key);
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if (i != end() && i->name == name) return i;
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return end();
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}
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Attr * get(const Symbol & name)
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{
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Attr key(name, 0);
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iterator i = std::lower_bound(begin(), end(), key);
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if (i != end() && i->name == name) return &*i;
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return nullptr;
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}
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Attr & need(const Symbol & name, const Pos & pos = noPos)
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{
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auto a = get(name);
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if (!a)
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throw Error({
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.msg = hintfmt("attribute '%s' missing", name),
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.errPos = pos
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});
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return *a;
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}
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iterator begin() { return &attrs[0]; }
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iterator end() { return &attrs[size_]; }
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Attr & operator[](size_t pos)
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{
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return attrs[pos];
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}
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void sort();
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size_t capacity() { return capacity_; }
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/* Returns the attributes in lexicographically sorted order. */
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std::vector<const Attr *> lexicographicOrder() const
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{
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std::vector<const Attr *> res;
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res.reserve(size_);
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for (size_t n = 0; n < size_; n++)
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res.emplace_back(&attrs[n]);
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std::sort(res.begin(), res.end(), [](const Attr * a, const Attr * b) {
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return (const string &) a->name < (const string &) b->name;
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});
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return res;
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}
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friend class EvalState;
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};
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}
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