Add base::get_absolute_path_from_relative() function

This addition is part of the solution for aseprite/aseprite#4851
which was a bug introduced in aseprite/asseprite#4389.

base/fs.cpp

@@ -216,6 +216,45 @@ std::string get_relative_path(const std::string& filename, const std::string& ba
   return relativePath;
 }
 
+std::string get_absolute_path_from_relative(const std::string& base_path,
+                                            const std::string& relative_filename)
+{
+  std::vector<std::string> absoluteParts;
+  split_string(base_path, absoluteParts, path_separators);
+
+  std::vector<std::string> relativeParts;
+  split_string(relative_filename, relativeParts, path_separators);
+
+  // If the first element is empty, it means that the relative
+  // file name starts with a separator and it also means that
+  // it's an absolute address.
+  if (relativeParts.size() >= 1 && relativeParts[0] == "")
+    return relative_filename;
+
+  bool relative_fn_browsable = false;
+  for (auto it = relativeParts.begin(); it != relativeParts.end(); ++it) {
+    if (*it == "..") {
+      relative_fn_browsable = true;
+      break;
+    }
+  }
+  if (!relative_fn_browsable)
+    return base::join_path(base_path, relative_filename);
+
+  for (auto it = relativeParts.begin(); it != relativeParts.end(); ++it) {
+    if (*it == "..")
+      absoluteParts.pop_back();
+    else
+      absoluteParts.push_back(*it);
+  }
+
+  std::string absolutePath = path_separators;
+  for (auto it = absoluteParts.begin(); it != absoluteParts.end(); ++it)
+    absolutePath = base::join_path(absolutePath, *it);
+
+  return absolutePath;
+}
+
 std::string join_path(const std::string& path, const std::string& file)
 {
   std::string result(path);

base/fs.h

@@ -87,49 +87,53 @@ inline constexpr bool is_path_separator(std::string::value_type chr)
     chr == '/');
 }
 
-// Returns only the path (without the last trailing slash).
-std::string get_file_path(const std::string& filename);
+  // Returns only the path (without the last trailing slash).
+  std::string get_file_path(const std::string& filename);
 
-// Returns the file name with its extension, removing the path.
-std::string get_file_name(const std::string& filename);
+  // Returns the file name with its extension, removing the path.
+  std::string get_file_name(const std::string& filename);
 
-// Returns the extension of the file name (without the dot).
-std::string get_file_extension(const std::string& filename);
+  // Returns the extension of the file name (without the dot).
+  std::string get_file_extension(const std::string& filename);
 
-// Returns the whole path with another extension.
-std::string replace_extension(const std::string& filename, const std::string& extension);
+  // Returns the whole path with another extension.
+  std::string replace_extension(const std::string& filename, const std::string& extension);
 
-// Returns the file name without path and without extension.
-std::string get_file_title(const std::string& filename);
-std::string get_file_title_with_path(const std::string& filename);
+  // Returns the file name without path and without extension.
+  std::string get_file_title(const std::string& filename);
+  std::string get_file_title_with_path(const std::string& filename);
 
-// Returns the relative path of the given filename from the base_path.
-std::string get_relative_path(const std::string& filename, const std::string& base_path);
+  // Returns the relative path of the given filename from the base_path.
+  std::string get_relative_path(const std::string& filename, const std::string& base_path);
 
-// Joins two paths or a path and a file name with a path-separator.
-std::string join_path(const std::string& path, const std::string& file);
+  // Returns the absolute path of a given relative filename referred to the base_path.
+  std::string get_absolute_path_from_relative(const std::string& base_path,
+                                              const std::string& relative_filename);
 
-// Removes the trailing separator from the given path.
-std::string remove_path_separator(const std::string& path);
+  // Joins two paths or a path and a file name with a path-separator.
+  std::string join_path(const std::string& path, const std::string& file);
 
-// Replaces all separators with the system separator.
-std::string fix_path_separators(const std::string& filename);
+  // Removes the trailing separator from the given path.
+  std::string remove_path_separator(const std::string& path);
 
-// Remove superfluous path elements ("/../" and "/./") and call
-// fix_path_separators() for the given path.
-std::string normalize_path(const std::string& path);
+  // Replaces all separators with the system separator.
+  std::string fix_path_separators(const std::string& filename);
 
-// Returns true if the filename contains one of the specified
-// extensions. The "extensions" parameter must be a set of possible
-// extensions.
-bool has_file_extension(const std::string& filename, const base::paths& extensions);
+  // Remove superfluous path elements ("/../" and "/./") and call
+  // fix_path_separators() for the given path.
+  std::string normalize_path(const std::string& path);
 
-int compare_filenames(const std::string& a, const std::string& b);
+  // Returns true if the filename contains one of the specified
+  // extensions. The "extensions" parameter must be a set of possible
+  // extensions.
+  bool has_file_extension(const std::string& filename, const base::paths& extensions);
+
+  int compare_filenames(const std::string& a, const std::string& b);
 
 #if LAF_WINDOWS
-class Version;
-Version get_file_version(const std::string& filename);
-Version get_file_version(const wchar_t* filename);
+  class Version;
+  Version get_file_version(const std::string& filename);
+  Version get_file_version(const wchar_t* filename);
 #endif
 
 } // namespace base

base/fs_tests.cpp

@@ -232,6 +232,25 @@ TEST(FS, GetRelativePath)
 #endif
 }
 
+TEST(FS, GetAbsolutePathFromRelativePath)
+{
+#if LAF_WINDOWS
+  EXPECT_EQ("C:\\foo\\bar\\test.file", get_absolute_path_from_relative("C:\\foo", "bar\\test.file"));
+  EXPECT_EQ("D:\\another\\disk\\foo\\bar\\test.file",
+                                       get_absolute_path_from_relative("D:\\another\\disk", "foo\\bar\\test.file"));
+  EXPECT_EQ("\\foo\\bar\\test.file",   get_absolute_path_from_relative("D:\\another\\disk", "\\foo\\bar\\test.file"));
+  EXPECT_EQ("C:\\foo\\bar\\test.file", get_absolute_path_from_relative("C:\\foo\\another", "..\\bar\\test.file"));
+  EXPECT_EQ("C:\\foo\\bar\\test.file", get_absolute_path_from_relative("C:\\foo\\a\\b", "..\\..\\bar\\test.file"));
+#else
+  EXPECT_EQ("C:/foo/bar/test.file",    get_absolute_path_from_relative("C:/foo", "bar/test.file"));
+  EXPECT_EQ("D:/another/disk/foo/bar/test.file",
+                                       get_absolute_path_from_relative("D:/another/disk", "foo/bar/test.file"));
+  EXPECT_EQ("/foo/bar/test.file",      get_absolute_path_from_relative("D:/another/disk", "/foo/bar/test.file"));
+  EXPECT_EQ("/foo/bar/test.file",      get_absolute_path_from_relative("/foo/another", "../bar/test.file"));
+  EXPECT_EQ("/foo/bar/test.file",      get_absolute_path_from_relative("/foo/a/b", "../../bar/test.file"));
+#endif
+}
+
 TEST(FS, GetAbsolutePath)
 {
   const auto cp = get_current_path();