Bug 1682031 - Add PathUtils.appendRelative r=emalysz

Differential Revision: https://phabricator.services.mozilla.com/D99505

dom/chrome-webidl/PathUtils.webidl

@@ -41,6 +41,15 @@ namespace PathUtils {
   [Throws]
   DOMString join(DOMString... components);
 
+  /**
+   * Join the given relative path to the base path.
+   *
+   * @param base The base path. This must be an absolute path.
+   * @param relativePath A relative path to join to the base path.
+   */
+  [Throws]
+  DOMString joinRelative(DOMString base, DOMString relativePath);
+
   /**
    * Normalize a path by removing multiple separators and `..` and `.`
    * directories.

dom/system/PathUtils.cpp

@@ -35,6 +35,7 @@ static constexpr auto ERROR_EMPTY_PATH =
     "PathUtils does not support empty paths"_ns;
 static constexpr auto ERROR_INITIALIZE_PATH = "Could not initialize path"_ns;
 static constexpr auto ERROR_GET_PARENT = "Could not get parent path"_ns;
+static constexpr auto ERROR_JOIN = "Could not append to path"_ns;
 
 static void ThrowError(ErrorResult& aErr, const nsresult aResult,
                        const nsCString& aMessage) {
@@ -163,7 +164,7 @@ void PathUtils::Join(const GlobalObject&, const Sequence<nsString>& aComponents,
   const auto components = Span<const nsString>(aComponents).Subspan(1);
   for (const auto& component : components) {
     if (nsresult rv = path->Append(component); NS_FAILED(rv)) {
-      ThrowError(aErr, rv, "Could not append to path"_ns);
+      ThrowError(aErr, rv, ERROR_JOIN);
       return;
     }
   }
@@ -171,6 +172,28 @@ void PathUtils::Join(const GlobalObject&, const Sequence<nsString>& aComponents,
   MOZ_ALWAYS_SUCCEEDS(path->GetPath(aResult));
 }
 
+void PathUtils::JoinRelative(const GlobalObject&, const nsAString& aBasePath,
+                             const nsAString& aRelativePath, nsString& aResult,
+                             ErrorResult& aErr) {
+  if (aRelativePath.IsEmpty()) {
+    aResult = aBasePath;
+    return;
+  }
+
+  nsCOMPtr<nsIFile> path = new nsLocalFile();
+  if (nsresult rv = path->InitWithPath(aBasePath); NS_FAILED(rv)) {
+    ThrowError(aErr, rv, ERROR_INITIALIZE_PATH);
+    return;
+  }
+
+  if (nsresult rv = path->AppendRelativePath(aRelativePath); NS_FAILED(rv)) {
+    ThrowError(aErr, rv, ERROR_JOIN);
+    return;
+  }
+
+  MOZ_ALWAYS_SUCCEEDS(path->GetPath(aResult));
+}
+
 void PathUtils::Normalize(const GlobalObject&, const nsAString& aPath,
                           nsString& aResult, ErrorResult& aErr) {
   if (aPath.IsEmpty()) {

dom/system/PathUtils.h

@@ -32,6 +32,10 @@ class PathUtils final {
   static void Join(const GlobalObject&, const Sequence<nsString>& aComponents,
                    nsString& aResult, ErrorResult& aErr);
 
+  static void JoinRelative(const GlobalObject&, const nsAString& aBasePath,
+                           const nsAString& aRelativePath, nsString& aResult,
+                           ErrorResult& aErr);
+
   static void Normalize(const GlobalObject&, const nsAString& aPath,
                         nsString& aResult, ErrorResult& aErr);
 

dom/system/tests/test_pathutils.html

@@ -22,6 +22,7 @@
 
   const UNRECOGNIZED_PATH = /Could not initialize path: NS_ERROR_FILE_UNRECOGNIZED_PATH/;
   const EMPTY_PATH = /PathUtils does not support empty paths/;
+  const JOIN = /Could not append to path/;
 
   add_task(function test_filename() {
     Assert.throws(
@@ -199,6 +200,34 @@
     }
   });
 
+  add_task(function test_join_relative() {
+    if (Services.appinfo.OS === "WINNT") {
+      is(
+        PathUtils.joinRelative("C:", ""),
+        "C:",
+        "PathUtils.joinRelative() with an empty relative path"
+      );
+
+      is(
+        PathUtils.joinRelative("C:", "foo\\bar\\baz"),
+        "C:\\foo\\bar\\baz",
+        "PathUtils.joinRelative() with a relative path containing path separators"
+      );
+    } else {
+      is(
+        PathUtils.joinRelative("/", ""),
+        "/",
+        "PathUtils.joinRelative() with an empty relative path"
+      );
+
+      is(
+        PathUtils.joinRelative("/", "foo/bar/baz"),
+        "/foo/bar/baz",
+        "PathUtils.joinRelative() with a relative path containing path separators"
+      );
+    }
+  });
+
   add_task(async function test_normalize() {
     Assert.throws(
       () => PathUtils.normalize(""),