pos-table.hh

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#pragma once
 
#include <cinttypes>
#include <numeric>
#include <vector>
 
#include "lix/libutil/chunked-vector.hh"
#include "lix/libexpr/pos-idx.hh"
#include "lix/libutil/position.hh"
#include "lix/libutil/sync.hh"
 
namespace nix {
 
class PosTable
{
public:
    class Origin
    {
        friend PosTable;
    private:
        uint32_t offset;
 
        Origin(Pos::Origin origin, uint32_t offset, size_t size):
            offset(offset), origin(origin), size(size)
        {}
 
    public:
        const Pos::Origin origin;
        const size_t size;
 
        uint32_t offsetOf(PosIdx p) const
        {
            return p.id - 1 - offset;
        }
    };
 
private:
    using Lines = std::vector<uint32_t>;
 
    std::map<uint32_t, Origin> origins;
    mutable Sync<std::map<uint32_t, Lines>> lines;
 
    const Origin * resolve(PosIdx p) const
    {
        if (p.id == 0)
            return nullptr;
 
        const auto idx = p.id - 1;
        /* we want the last key <= idx, so we'll take prev(first key > idx).
            this is guaranteed to never rewind origin.begin because the first
            key is always 0. */
        const auto pastOrigin = origins.upper_bound(idx);
        return &std::prev(pastOrigin)->second;
    }
 
public:
    Origin addOrigin(Pos::Origin origin, size_t size)
    {
        uint32_t offset = 0;
        if (auto it = origins.rbegin(); it != origins.rend())
            offset = it->first + it->second.size;
        // +1 because all PosIdx are offset by 1 to begin with (because noPos == 0), and
        // another +1 to ensure that all origins can point to EOF, eg on (invalid) empty inputs.
        if (2 + offset + size < offset)
            return Origin{origin, offset, 0};
        return origins.emplace(offset, Origin{origin, offset, size}).first->second;
    }
 
    PosIdx add(const Origin & origin, size_t offset)
    {
        if (offset > origin.size)
            return PosIdx();
        return PosIdx(1 + origin.offset + offset);
    }
 
    Pos operator[](PosIdx p) const;
 
    Pos::Origin originOf(PosIdx p) const
    {
        if (auto o = resolve(p))
            return o->origin;
        return std::monostate{};
    }
};
 
}