Fix base::get_absolute_path() fixing base::normalize_path() function

base::get_absolute_path() resulted in bugs when more than two or more
double dots were present in the input path.
The source of the error was the base::normalize_path() function
which has been fixed.
Also it was fixed a couple of tests from fs_tests.cpp, and added more.
This fiix is part of the solution of aseprite/aseprite#4851.

base/fs.cpp

@@ -281,66 +281,36 @@ std::string normalize_path(const std::string& _path)
   // Replace multiple slashes with a single path_separator.
   std::string path = fix_path_separators(_path);
 
-  std::string fn;
-  fn.reserve(path.size());
-
-  // Add the first separator for absolute paths.
-  if (!path.empty() && path[0] == path_separator) {
-    fn.push_back(path_separator);
-
-#if LAF_WINDOWS
-    // Add the second separator for network paths.
-    if (path.size() >= 2 && path[1] == path_separator) {
-      fn.push_back(path_separator);
-    }
-#endif
-  }
-
   std::vector<std::string> parts;
   split_string(path, parts, path_separators);
 
-  // Last element generates a final dot or slash in normalized path.
-  bool last_dot = false;
-
-  auto n = int(parts.size());
-  for (int i = 0; i < n; ++i) {
-    const auto& part = parts[i];
-
-    // Remove each dot part.
-    if (part == ".") {
-      last_dot = true;
+  std::vector<std::string> fn_parts;
+  bool has_root = (!_path.empty() && _path[0] == path_separator);
 
-      if (i + 1 == n)
-        break;
-
-      fn = join_path(fn, std::string());
+  for (const auto& part : parts) {
+    // Skip each dot part.
+    if (part.empty() || part == ".")
       continue;
-    }
-
-    if (!part.empty())
-      last_dot = false;
-
-    if (part != ".." && i + 1 < n && parts[i + 1] == "..") {
-      // Skip this "part/.."
-      ++i;
-      last_dot = true;
-    }
-    else if (!part.empty()) {
-      fn = join_path(fn, part);
+    else if (part == "..") {
+      if (has_root && fn_parts.empty())
+        continue;
+      if (!fn_parts.empty() && fn_parts.back() != "..")
+        fn_parts.pop_back();
+      else
+        fn_parts.push_back(part);
     }
     else
-      last_dot = true;
+      fn_parts.push_back(part);
   }
-  if (last_dot) {
-    if (fn.empty())
-      fn = ".";
-    else if (fn.back() != path_separator &&
-             // Don't include trailing slash for ".." filename
-             get_file_name(fn) != "..") {
-      fn.push_back(path_separator);
-    }
-  }
-  return fn;
+
+  // Reconstruct the filename 'fn' from 'fn_parts'
+  std::string fn;
+  if (has_root)
+    fn = join_path(fn, {path_separator});
+  for (const auto& part : fn_parts)
+    fn = join_path(fn, part);
+
+  return (fn.empty() ? "." : fn);
 }
 
 bool has_file_extension(const std::string& filename, const base::paths& extensions)

base/fs_tests.cpp

@@ -245,8 +245,14 @@ TEST(FS, GetAbsolutePath)
 
 #if LAF_WINDOWS
   EXPECT_EQ("C:\\file", get_absolute_path("C:/path/../file"));
+  EXPECT_EQ("C:\\user\\file", get_absolute_path("C:/user/name/path/../../file"));
+  EXPECT_EQ("C:\\file", get_absolute_path("C:/user/name/path/../../../file"));
+  EXPECT_EQ("C:\\path\\file", get_absolute_path("C:/user/name/..//.././path/tag/../file"));
 #else
   EXPECT_EQ("/file", get_absolute_path("/path/../file"));
+  EXPECT_EQ("/user/file", get_absolute_path("/user/name/path/../../file"));
+  EXPECT_EQ("/file", get_absolute_path("/user/name/path/../../../file"));
+  EXPECT_EQ("/path/file", get_absolute_path("/user/name/..//.././path/tag/../file"));
 #endif
 }
 
@@ -274,8 +280,8 @@ TEST(FS, NormalizePath)
   EXPECT_EQ(".", normalize_path(".///./."));
   EXPECT_EQ(".", normalize_path(".///./"));
 
-  EXPECT_EQ("a" + sep, normalize_path("a/."));
-  EXPECT_EQ("a" + sep, normalize_path("a/"));
+  EXPECT_EQ("a", normalize_path("a/."));
+  EXPECT_EQ("a", normalize_path("a/"));
   EXPECT_EQ("a", normalize_path("./a"));
   EXPECT_EQ("a" + sep + "b" + sep + "c", normalize_path("a///b/./c"));
 
@@ -288,6 +294,7 @@ TEST(FS, NormalizePath)
   EXPECT_EQ(".", normalize_path("a/.."));
   EXPECT_EQ("..", normalize_path("../a/.."));
   EXPECT_EQ(".." + sep + "..", normalize_path("../a/../.."));
+  EXPECT_EQ(".." + sep + "..", normalize_path("../a/../../"));
   EXPECT_EQ("..", normalize_path("a/../.."));
   EXPECT_EQ(sep + "b", normalize_path("/a/../b"));