Remove unused Rust stuff

In particular we were still compiling rust-ffi.cc even though we're
not using it.

src/libutil/rust-ffi.cc

@@ -1,24 +0,0 @@
-#if 0
-#include "logging.hh"
-#include "rust-ffi.hh"
-
-extern "C" std::exception_ptr * make_error(rust::StringSlice s)
-{
-    return new std::exception_ptr(std::make_exception_ptr(nix::Error(std::string(s.ptr, s.size))));
-}
-
-extern "C" void destroy_error(std::exception_ptr * ex)
-{
-    free(ex);
-}
-
-namespace rust {
-
-std::ostream & operator << (std::ostream & str, const String & s)
-{
-    str << (std::string_view) s;
-    return str;
-}
-
-}
-#endif

src/libutil/rust-ffi.hh

@@ -1,189 +0,0 @@
-#pragma once
-#if 0
-
-#include "serialise.hh"
-
-#include <string_view>
-#include <cstring>
-#include <array>
-
-namespace rust {
-
-typedef void (*DropFun)(void *);
-
-/* A Rust value of N bytes. It can be moved but not copied. When it
-   goes out of scope, the C++ destructor will run the drop
-   function. */
-template<std::size_t N, DropFun drop>
-struct Value
-{
-protected:
-
-    std::array<char, N> raw;
-
-    ~Value()
-    {
-        if (!isEvacuated()) {
-            drop(this);
-            evacuate();
-        }
-    }
-
-    // Must not be called directly.
-    Value()
-    { }
-
-    Value(Value && other)
-        : raw(other.raw)
-    {
-        other.evacuate();
-    }
-
-    void operator =(Value && other)
-    {
-        if (!isEvacuated())
-            drop(this);
-        raw = other.raw;
-        other.evacuate();
-    }
-
-private:
-
-    /* FIXME: optimize these (ideally in such a way that the compiler
-       can elide most calls to evacuate() / isEvacuated(). */
-    inline void evacuate()
-    {
-        for (auto & i : raw) i = 0;
-    }
-
-    inline bool isEvacuated()
-    {
-        for (auto & i : raw)
-            if (i != 0) return false;
-        return true;
-    }
-};
-
-/* A Rust vector. */
-template<typename T, DropFun drop>
-struct Vec : Value<3 * sizeof(void *), drop>
-{
-    inline size_t size() const
-    {
-        return ((const size_t *) &this->raw)[2];
-    }
-
-    const T * data() const
-    {
-        return ((const T * *) &this->raw)[0];
-    }
-};
-
-/* A Rust slice. */
-template<typename T>
-struct Slice
-{
-    const T * ptr;
-    size_t size;
-
-    Slice(const T * ptr, size_t size) : ptr(ptr), size(size)
-    {
-        assert(ptr);
-    }
-};
-
-struct StringSlice : Slice<char>
-{
-    StringSlice(const std::string & s): Slice(s.data(), s.size()) {}
-    explicit StringSlice(std::string_view s): Slice(s.data(), s.size()) {}
-    StringSlice(const char * s): Slice(s, strlen(s)) {}
-
-    operator std::string_view() const
-    {
-        return std::string_view(ptr, size);
-    }
-};
-
-/* A Rust string. */
-struct String;
-
-extern "C" {
-    void ffi_String_new(StringSlice s, String * out);
-    void ffi_String_drop(void * s);
-}
-
-struct String : Vec<char, ffi_String_drop>
-{
-    String() = delete;
-
-    String(std::string_view s)
-    {
-        ffi_String_new(StringSlice(s), this);
-    }
-
-    String(const char * s)
-        : String({s, std::strlen(s)})
-    {
-    }
-
-    operator std::string_view() const
-    {
-        return std::string_view(data(), size());
-    }
-};
-
-std::ostream & operator << (std::ostream & str, const String & s);
-
-/* C++ representation of Rust's Result<T, CppException>. */
-template<typename T>
-struct Result
-{
-    enum { Ok = 0, Err = 1, Uninit = 2 } tag;
-
-    union {
-        T data;
-        std::exception_ptr * exc;
-    };
-
-    Result() : tag(Uninit) { }; // FIXME: remove
-
-    Result(const Result &) = delete;
-
-    Result(Result && other)
-        : tag(other.tag)
-    {
-        other.tag = Uninit;
-        if (tag == Ok)
-            data = std::move(other.data);
-        else if (tag == Err)
-            exc = other.exc;
-    }
-
-    ~Result()
-    {
-        if (tag == Ok)
-            data.~T();
-        else if (tag == Err)
-            free(exc);
-        else if (tag == Uninit)
-            ;
-        else
-            abort();
-    }
-
-    /* Rethrow the wrapped exception or return the wrapped value. */
-    T unwrap()
-    {
-        if (tag == Ok) {
-            tag = Uninit;
-            return std::move(data);
-        }
-        else if (tag == Err)
-            std::rethrow_exception(*exc);
-        else
-            abort();
-    }
-};
-
-}
-#endif