Backport SourcePath from the lazy-trees branch

This introduces the SourcePath type from lazy-trees as an abstraction
for accessing files from inputs that may not be materialized in the
real filesystem (e.g. Git repositories). Currently, however, it's just
a wrapper around CanonPath, so it shouldn't change any behaviour. (On
lazy-trees, SourcePath is a <InputAccessor, CanonPath> tuple.)

2 files changed, 249 insertions, 0 deletions

diff --git a/src/libfetchers/input-accessor.cc b/src/libfetchers/input-accessor.cc
new file mode 100644
index 000000000..f9909c218
--- /dev/null
+++ b/src/libfetchers/input-accessor.cc
@@ -0,0 +1,100 @@
+#include "input-accessor.hh"
+#include "store-api.hh"
+
+namespace nix {
+
+std::ostream & operator << (std::ostream & str, const SourcePath & path)
+{
+    str << path.to_string();
+    return str;
+}
+
+std::string_view SourcePath::baseName() const
+{
+    return path.baseName().value_or("source");
+}
+
+SourcePath SourcePath::parent() const
+{
+    auto p = path.parent();
+    assert(p);
+    return std::move(*p);
+}
+
+InputAccessor::Stat SourcePath::lstat() const
+{
+    auto st = nix::lstat(path.abs());
+    return InputAccessor::Stat {
+        .type =
+            S_ISREG(st.st_mode) ? InputAccessor::tRegular :
+            S_ISDIR(st.st_mode) ? InputAccessor::tDirectory :
+            S_ISLNK(st.st_mode) ? InputAccessor::tSymlink :
+            InputAccessor::tMisc,
+        .isExecutable = S_ISREG(st.st_mode) && st.st_mode & S_IXUSR
+    };
+}
+
+std::optional<InputAccessor::Stat> SourcePath::maybeLstat() const
+{
+    // FIXME: merge these into one operation.
+    if (!pathExists())
+        return {};
+    return lstat();
+}
+
+InputAccessor::DirEntries SourcePath::readDirectory() const
+{
+    InputAccessor::DirEntries res;
+    for (auto & entry : nix::readDirectory(path.abs())) {
+        std::optional<InputAccessor::Type> type;
+        switch (entry.type) {
+        case DT_REG: type = InputAccessor::Type::tRegular; break;
+        case DT_LNK: type = InputAccessor::Type::tSymlink; break;
+        case DT_DIR: type = InputAccessor::Type::tDirectory; break;
+        }
+        res.emplace(entry.name, type);
+    }
+    return res;
+}
+
+StorePath SourcePath::fetchToStore(
+    ref<Store> store,
+    std::string_view name,
+    PathFilter * filter,
+    RepairFlag repair) const
+{
+    return
+        settings.readOnlyMode
+        ? store->computeStorePathForPath(name, path.abs(), FileIngestionMethod::Recursive, htSHA256, filter ? *filter : defaultPathFilter).first
+        : store->addToStore(name, path.abs(), FileIngestionMethod::Recursive, htSHA256, filter ? *filter : defaultPathFilter, repair);
+}
+
+SourcePath SourcePath::resolveSymlinks() const
+{
+    SourcePath res(CanonPath::root);
+
+    int linksAllowed = 1024;
+
+    for (auto & component : path) {
+        res.path.push(component);
+        while (true) {
+            if (auto st = res.maybeLstat()) {
+                if (!linksAllowed--)
+                    throw Error("infinite symlink recursion in path '%s'", path);
+                if (st->type != InputAccessor::tSymlink) break;
+                auto target = res.readLink();
+                if (hasPrefix(target, "/"))
+                    res = CanonPath(target);
+                else {
+                    res.path.pop();
+                    res.path.extend(CanonPath(target));
+                }
+            } else
+                break;
+        }
+    }
+
+    return res;
+}
+
+}
diff --git a/src/libfetchers/input-accessor.hh b/src/libfetchers/input-accessor.hh
new file mode 100644
index 000000000..23c510d4d
--- /dev/null
+++ b/src/libfetchers/input-accessor.hh
@@ -0,0 +1,149 @@
+#pragma once
+
+#include "ref.hh"
+#include "types.hh"
+#include "archive.hh"
+#include "canon-path.hh"
+#include "repair-flag.hh"
+
+namespace nix {
+
+class StorePath;
+class Store;
+
+struct InputAccessor
+{
+    enum Type { tRegular, tSymlink, tDirectory, tMisc };
+
+    struct Stat
+    {
+        Type type = tMisc;
+        //uint64_t fileSize = 0; // regular files only
+        bool isExecutable = false; // regular files only
+    };
+
+    typedef std::optional<Type> DirEntry;
+
+    typedef std::map<std::string, DirEntry> DirEntries;
+};
+
+/**
+ * An abstraction for accessing source files during
+ * evaluation. Currently, it's just a wrapper around `CanonPath` that
+ * accesses files in the regular filesystem, but in the future it will
+ * support fetching files in other ways.
+ */
+struct SourcePath
+{
+    CanonPath path;
+
+    SourcePath(CanonPath path)
+        : path(std::move(path))
+    { }
+
+    std::string_view baseName() const;
+
+    /**
+     * Construct the parent of this `SourcePath`. Aborts if `this`
+     * denotes the root.
+     */
+    SourcePath parent() const;
+
+    /**
+     * If this `SourcePath` denotes a regular file (not a symlink),
+     * return its contents; otherwise throw an error.
+     */
+    std::string readFile() const
+    { return nix::readFile(path.abs()); }
+
+    /**
+     * Return whether this `SourcePath` denotes a file (of any type)
+     * that exists
+    */
+    bool pathExists() const
+    { return nix::pathExists(path.abs()); }
+
+    /**
+     * Return stats about this `SourcePath`, or throw an exception if
+     * it doesn't exist.
+     */
+    InputAccessor::Stat lstat() const;
+
+    /**
+     * Return stats about this `SourcePath`, or std::nullopt if it
+     * doesn't exist.
+     */
+    std::optional<InputAccessor::Stat> maybeLstat() const;
+
+    /**
+     * If this `SourcePath` denotes a directory (not a symlink),
+     * return its directory entries; otherwise throw an error.
+     */
+    InputAccessor::DirEntries readDirectory() const;
+
+    /**
+     * If this `SourcePath` denotes a symlink, return its target;
+     * otherwise throw an error.
+     */
+    std::string readLink() const
+    { return nix::readLink(path.abs()); }
+
+    /**
+     * Dump this `SourcePath` to `sink` as a NAR archive.
+     */
+    void dumpPath(
+        Sink & sink,
+        PathFilter & filter = defaultPathFilter) const
+    { return nix::dumpPath(path.abs(), sink, filter); }
+
+    /**
+     * Copy this `SourcePath` to the Nix store.
+     */
+    StorePath fetchToStore(
+        ref<Store> store,
+        std::string_view name = "source",
+        PathFilter * filter = nullptr,
+        RepairFlag repair = NoRepair) const;
+
+    /**
+     * Return the location of this path in the "real" filesystem, if
+     * it has a physical location.
+     */
+    std::optional<CanonPath> getPhysicalPath() const
+    { return path; }
+
+    std::string to_string() const
+    { return path.abs(); }
+
+    SourcePath operator + (const CanonPath & x) const
+    { return {path + x}; }
+
+    SourcePath operator + (std::string_view c) const
+    {  return {path + c}; }
+
+    bool operator == (const SourcePath & x) const
+    {
+        return path == x.path;
+    }
+
+    bool operator != (const SourcePath & x) const
+    {
+        return path != x.path;
+    }
+
+    bool operator < (const SourcePath & x) const
+    {
+        return path < x.path;
+    }
+
+    /**
+     * Resolve any symlinks in this `SourcePath` (including its
+     * parents). The result is a `SourcePath` in which no element is a
+     * symlink.
+     */
+    SourcePath resolveSymlinks() const;
+};
+
+std::ostream & operator << (std::ostream & str, const SourcePath & path);
+
+}