5 files changed, 147 insertions, 21 deletions

diff --git a/src/libutil/rust-ffi.cc b/src/libutil/rust-ffi.cc
index 931d29542..accc5e22b 100644
--- a/src/libutil/rust-ffi.cc
+++ b/src/libutil/rust-ffi.cc
@@ -1,12 +1,18 @@
 #include "logging.hh"
 #include "rust-ffi.hh"
 
-namespace nix {
-
 extern "C" std::exception_ptr * make_error(rust::StringSlice s)
 {
     // FIXME: leak
-    return new std::exception_ptr(std::make_exception_ptr(Error(std::string(s.ptr, s.size))));
+    return new std::exception_ptr(std::make_exception_ptr(nix::Error(std::string(s.ptr, s.size))));
+}
+
+namespace rust {
+
+std::ostream & operator << (std::ostream & str, const String & s)
+{
+    str << (std::string_view) s;
+    return str;
 }
 
 }
diff --git a/src/libutil/rust-ffi.hh b/src/libutil/rust-ffi.hh
index 663758bfc..a77f83ac5 100644
--- a/src/libutil/rust-ffi.hh
+++ b/src/libutil/rust-ffi.hh
@@ -1,16 +1,91 @@
+#pragma once
+
 #include "serialise.hh"
 
+#include <string_view>
+#include <cstring>
+#include <array>
+
 namespace rust {
 
-// Depending on the internal representation of Rust slices is slightly
-// evil...
+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
 {
-    T * ptr;
+    const T * ptr;
     size_t size;
 
-    Slice(T * ptr, size_t size) : ptr(ptr), size(size)
+    Slice(const T * ptr, size_t size) : ptr(ptr), size(size)
     {
         assert(ptr);
     }
@@ -18,9 +93,44 @@ struct Slice
 
 struct StringSlice : Slice<char>
 {
-    StringSlice(const std::string & s): Slice((char *) s.data(), s.size()) {}
+    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(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);
+
 struct Source
 {
     size_t (*fun)(void * source_this, rust::Slice<uint8_t> data);
@@ -33,7 +143,7 @@ struct Source
     // FIXME: how to propagate exceptions?
     static size_t sourceWrapper(void * _this, rust::Slice<uint8_t> data)
     {
-        auto n = ((nix::Source *) _this)->read(data.ptr, data.size);
+        auto n = ((nix::Source *) _this)->read((unsigned char *) data.ptr, data.size);
         return n;
     }
 };
@@ -49,11 +159,20 @@ struct Result
         std::exception_ptr * exc;
     };
 
+    ~Result()
+    {
+        if (tag == 0)
+            data.~T();
+        else if (tag == 1)
+            // FIXME: don't leak exc
+            ;
+    }
+
     /* Rethrow the wrapped exception or return the wrapped value. */
     T unwrap()
     {
         if (tag == 0)
-            return data;
+            return std::move(data);
         else if (tag == 1)
             std::rethrow_exception(*exc);
         else
diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 2cc7793fd..262bc655f 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -17,7 +17,7 @@ void unpackTarfile(Source & source, const Path & destDir)
 void unpackTarfile(const Path & tarFile, const Path & destDir,
     std::optional<std::string> baseName)
 {
-    if (!baseName) baseName = baseNameOf(tarFile);
+    if (!baseName) baseName = std::string(baseNameOf(tarFile));
 
     auto source = sinkToSource([&](Sink & sink) {
         // FIXME: look at first few bytes to determine compression type.
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index b4d444a67..e67bdcdeb 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -188,22 +188,22 @@ Path dirOf(const Path & path)
 }
 
 
-string baseNameOf(const Path & path)
+std::string_view baseNameOf(std::string_view path)
 {
     if (path.empty())
         return "";
 
-    Path::size_type last = path.length() - 1;
+    auto last = path.size() - 1;
     if (path[last] == '/' && last > 0)
         last -= 1;
 
-    Path::size_type pos = path.rfind('/', last);
+    auto pos = path.rfind('/', last);
     if (pos == string::npos)
         pos = 0;
     else
         pos += 1;
 
-    return string(path, pos, last - pos + 1);
+    return path.substr(pos, last - pos + 1);
 }
 
 
@@ -1302,9 +1302,10 @@ bool hasPrefix(const string & s, const string & prefix)
 }
 
 
-bool hasSuffix(const string & s, const string & suffix)
+bool hasSuffix(std::string_view s, std::string_view suffix)
 {
-    return s.size() >= suffix.size() && string(s, s.size() - suffix.size()) == suffix;
+    return s.size() >= suffix.size()
+        && s.substr(s.size() - suffix.size()) == suffix;
 }
 
 
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index a1acb49b5..abd91b81c 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -62,7 +62,7 @@ Path dirOf(const Path & path);
 
 /* Return the base name of the given canonical path, i.e., everything
    following the final `/'. */
-string baseNameOf(const Path & path);
+std::string_view baseNameOf(std::string_view path);
 
 /* Check whether 'path' is a descendant of 'dir'. */
 bool isInDir(const Path & path, const Path & dir);
@@ -407,7 +407,7 @@ bool hasPrefix(const string & s, const string & prefix);
 
 
 /* Return true iff `s' ends in `suffix'. */
-bool hasSuffix(const string & s, const string & suffix);
+bool hasSuffix(std::string_view s, std::string_view suffix);
 
 
 /* Convert a string to lower case. */
@@ -450,10 +450,10 @@ string base64Decode(const string & s);
 /* Get a value for the specified key from an associate container, or a
    default value if the key doesn't exist. */
 template <class T>
-string get(const T & map, const string & key, const string & def = "")
+std::optional<std::string> get(const T & map, const std::string & key)
 {
     auto i = map.find(key);
-    return i == map.end() ? def : i->second;
+    return i == map.end() ? std::optional<std::string>() : i->second;
 }