Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libutil/source-accessor.cc

@@ -0,0 +1,108 @@
+#include "source-accessor.hh"
+#include "archive.hh"
+
+namespace nix {
+
+static std::atomic<size_t> nextNumber{0};
+
+SourceAccessor::SourceAccessor()
+    : number(++nextNumber)
+    , displayPrefix{"«unknown»"}
+{
+}
+
+bool SourceAccessor::pathExists(const CanonPath & path)
+{
+    return maybeLstat(path).has_value();
+}
+
+std::string SourceAccessor::readFile(const CanonPath & path)
+{
+    StringSink sink;
+    std::optional<uint64_t> size;
+    readFile(path, sink, [&](uint64_t _size)
+    {
+        size = _size;
+    });
+    assert(size && *size == sink.s.size());
+    return std::move(sink.s);
+}
+
+void SourceAccessor::readFile(
+    const CanonPath & path,
+    Sink & sink,
+    std::function<void(uint64_t)> sizeCallback)
+{
+    auto s = readFile(path);
+    sizeCallback(s.size());
+    sink(s);
+}
+
+Hash SourceAccessor::hashPath(
+    const CanonPath & path,
+    PathFilter & filter,
+    HashAlgorithm ha)
+{
+    HashSink sink(ha);
+    dumpPath(path, sink, filter);
+    return sink.finish().first;
+}
+
+SourceAccessor::Stat SourceAccessor::lstat(const CanonPath & path)
+{
+    if (auto st = maybeLstat(path))
+        return *st;
+    else
+        throw FileNotFound("path '%s' does not exist", showPath(path));
+}
+
+void SourceAccessor::setPathDisplay(std::string displayPrefix, std::string displaySuffix)
+{
+    this->displayPrefix = std::move(displayPrefix);
+    this->displaySuffix = std::move(displaySuffix);
+}
+
+std::string SourceAccessor::showPath(const CanonPath & path)
+{
+    return displayPrefix + path.abs() + displaySuffix;
+}
+
+CanonPath SourceAccessor::resolveSymlinks(
+    const CanonPath & path,
+    SymlinkResolution mode)
+{
+    auto res = CanonPath::root;
+
+    int linksAllowed = 1024;
+
+    std::list<std::string> todo;
+    for (auto & c : path)
+        todo.push_back(std::string(c));
+
+    while (!todo.empty()) {
+        auto c = *todo.begin();
+        todo.pop_front();
+        if (c == "" || c == ".")
+            ;
+        else if (c == "..")
+            res.pop();
+        else {
+            res.push(c);
+            if (mode == SymlinkResolution::Full || !todo.empty()) {
+                if (auto st = maybeLstat(res); st && st->type == SourceAccessor::tSymlink) {
+                    if (!linksAllowed--)
+                        throw Error("infinite symlink recursion in path '%s'", showPath(path));
+                    auto target = readLink(res);
+                    res.pop();
+                    if (hasPrefix(target, "/"))
+                        res = CanonPath::root;
+                    todo.splice(todo.begin(), tokenizeString<std::list<std::string>>(target, "/"));
+                }
+            }
+        }
+    }
+
+    return res;
+}
+
+}