Move most of InputAccessor into libutil

src/libutil/source-accessor.hh

@@ -0,0 +1,96 @@
+#pragma once
+
+#include "canon-path.hh"
+#include "hash.hh"
+
+namespace nix {
+
+/**
+ * A read-only filesystem abstraction. This is used by the Nix
+ * evaluator and elsewhere for accessing sources in various
+ * filesystem-like entities (such as the real filesystem, tarballs or
+ * Git repositories).
+ */
+struct SourceAccessor
+{
+    const size_t number;
+
+    SourceAccessor();
+
+    virtual ~SourceAccessor()
+    { }
+
+    virtual std::string readFile(const CanonPath & path) = 0;
+
+    virtual bool pathExists(const CanonPath & path) = 0;
+
+    enum Type {
+      tRegular, tSymlink, tDirectory,
+      /**
+        Any other node types that may be encountered on the file system, such as device nodes, sockets, named pipe, and possibly even more exotic things.
+
+        Responsible for `"unknown"` from `builtins.readFileType "/dev/null"`.
+
+        Unlike `DT_UNKNOWN`, this must not be used for deferring the lookup of types.
+      */
+      tMisc
+    };
+
+    struct Stat
+    {
+        Type type = tMisc;
+        //uint64_t fileSize = 0; // regular files only
+        bool isExecutable = false; // regular files only
+    };
+
+    virtual Stat lstat(const CanonPath & path) = 0;
+
+    std::optional<Stat> maybeLstat(const CanonPath & path);
+
+    typedef std::optional<Type> DirEntry;
+
+    typedef std::map<std::string, DirEntry> DirEntries;
+
+    virtual DirEntries readDirectory(const CanonPath & path) = 0;
+
+    virtual std::string readLink(const CanonPath & path) = 0;
+
+    virtual void dumpPath(
+        const CanonPath & path,
+        Sink & sink,
+        PathFilter & filter = defaultPathFilter);
+
+    Hash hashPath(
+        const CanonPath & path,
+        PathFilter & filter = defaultPathFilter,
+        HashType ht = htSHA256);
+
+    /* Return a corresponding path in the root filesystem, if
+       possible. This is only possible for filesystems that are
+       materialized in the root filesystem. */
+    virtual std::optional<CanonPath> getPhysicalPath(const CanonPath & path)
+    { return std::nullopt; }
+
+    bool operator == (const SourceAccessor & x) const
+    {
+        return number == x.number;
+    }
+
+    bool operator < (const SourceAccessor & x) const
+    {
+        return number < x.number;
+    }
+
+    void setPathDisplay(std::string displayPrefix, std::string displaySuffix = "");
+
+    virtual std::string showPath(const CanonPath & path);
+
+    /* Return the maximum last-modified time of the files in this
+       tree, if available. */
+    virtual std::optional<time_t> getLastModified()
+    {
+        return std::nullopt;
+    }
+};
+
+}