Move 'normalize_path' into path.cpp

src/path.cpp

@@ -21,6 +21,49 @@
 
 namespace quickbook
 {
+    // Convert the path to its canonical representation if it exists.
+    // Or something close if it doesn't.
+    fs::path normalize_path(fs::path const& path)
+    {
+        fs::path p = fs::absolute(path); // The base of the path.
+        fs::path extra; // The non-existant part of the path.
+        int parent_count = 0; // Number of active '..' sections
+
+        // Invariant: path is equivalent to: p / ('..' * parent_count) / extra
+        // i.e. if parent_count == 0: p/extra
+        // if parent_count == 2: p/../../extra
+
+        // Pop path sections from path until we find an existing
+        // path, adjusting for any dot path sections.
+        while (!fs::exists(fs::status(p))) {
+            fs::path name = p.filename();
+            p = p.parent_path();
+            if (name == "..") {
+                ++parent_count;
+            }
+            else if (name == ".") {
+            }
+            else if (parent_count) {
+                --parent_count;
+            }
+            else {
+                extra = name / extra;
+            }
+        }
+
+        // If there are any left over ".." sections, then add them
+        // on to the end of the real path, and trust Boost.Filesystem
+        // to sort them out.
+        while (parent_count) {
+            p = p / "..";
+            --parent_count;
+        }
+
+        // Cannoicalize the existing part of the path, and add 'extra' back to
+        // the end.
+        return fs::canonical(p) / extra;
+    }
+
     // Not a general purpose normalization function, just
     // from paths from the root directory. It strips the excess
     // ".." parts from a path like: "x/../../y", leaving "y".