Allow special characters in flake paths

Support using nix flakes in paths with spaces or abitrary unicode characters.
This introduces the convention that the path part of the URL should be
percent-encoded when dealing with `path:` urls and not when using
filepaths (following the convention of firefox).

Co-authored-by: Rendal <rasmus@rend.al>

src/libexpr/flake/flakeref.cc

@@ -77,14 +77,6 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
 {
     using namespace fetchers;
 
-    static std::string fnRegex = "[0-9a-zA-Z-._~!$&'\"()*+,;=]+";
-
-    static std::regex pathUrlRegex(
-        "(/?" + fnRegex + "(?:/" + fnRegex + ")*/?)"
-        + "(?:\\?(" + queryRegex + "))?"
-        + "(?:#(" + queryRegex + "))?",
-        std::regex::ECMAScript);
-
     static std::regex flakeRegex(
         "((" + flakeIdRegexS + ")(?:/(?:" + refAndOrRevRegex + "))?)"
         + "(?:#(" + queryRegex + "))?",
@@ -92,26 +84,23 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
 
     std::smatch match;
 
-    /* Check if 'url' is a flake ID. This is an abbreviated syntax for
-       'flake:<flake-id>?ref=<ref>&rev=<rev>'. */
-
-    if (std::regex_match(url, match, flakeRegex)) {
-        auto parsedURL = ParsedURL{
-            .url = url,
-            .base = "flake:" + match.str(1),
-            .scheme = "flake",
-            .authority = "",
-            .path = match[1],
-        };
-
-        return std::make_pair(
-            FlakeRef(Input::fromURL(parsedURL, isFlake), ""),
-            percentDecode(match.str(6)));
-    }
-
-    else if (std::regex_match(url, match, pathUrlRegex)) {
-        std::string path = match[1];
-        std::string fragment = percentDecode(match.str(3));
+    auto parsePathFlakeRef = [&]() {
+        std::string path = url;
+        std::string fragment = "";
+        std::map<std::string, std::string> query = {};
+        auto pathEnd = url.find_first_of("#?");
+        auto fragmentStart = pathEnd;
+        if (pathEnd != std::string::npos && url[pathEnd] == '?')
+            fragmentStart = url.find("#");
+        if (pathEnd != std::string::npos) {
+            path = url.substr(0, pathEnd);
+        }
+        if (fragmentStart != std::string::npos) {
+            fragment = percentDecode(url.substr(fragmentStart+1));
+        }
+        if (fragmentStart != std::string::npos && pathEnd != std::string::npos) {
+            query = decodeQuery(url.substr(pathEnd+1, fragmentStart));
+        }
 
         if (baseDir) {
             /* Check if 'url' is a path (either absolute or relative
@@ -163,7 +152,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                             .scheme = "git+file",
                             .authority = "",
                             .path = flakeRoot,
-                            .query = decodeQuery(match[2]),
+                            .query = query,
                         };
 
                         if (subdir != "") {
@@ -188,7 +177,6 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         } else {
             if (!hasPrefix(path, "/"))
                 throw BadURL("flake reference '%s' is not an absolute path", url);
-            auto query = decodeQuery(match[2]);
             path = canonPath(path + "/" + getOr(query, "dir", ""));
         }
 
@@ -197,19 +185,40 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         attrs.insert_or_assign("path", path);
 
         return std::make_pair(FlakeRef(Input::fromAttrs(std::move(attrs)), ""), fragment);
+    };
+
+    /* Check if 'url' is a flake ID. This is an abbreviated syntax for
+       'flake:<flake-id>?ref=<ref>&rev=<rev>'. */
+
+    if (std::regex_match(url, match, flakeRegex)) {
+        auto parsedURL = ParsedURL{
+            .url = url,
+            .base = "flake:" + match.str(1),
+            .scheme = "flake",
+            .authority = "",
+            .path = match[1],
+        };
+
+        return std::make_pair(
+            FlakeRef(Input::fromURL(parsedURL), ""),
+            percentDecode(match.str(6)));
     }
 
     else {
-        auto parsedURL = parseURL(url);
-        std::string fragment;
-        std::swap(fragment, parsedURL.fragment);
+        try {
+            auto parsedURL = parseURL(url);
+            std::string fragment;
+            std::swap(fragment, parsedURL.fragment);
 
-        auto input = Input::fromURL(parsedURL, isFlake);
-        input.parent = baseDir;
+            auto input = Input::fromURL(parsedURL, isFlake);
+            input.parent = baseDir;
 
-        return std::make_pair(
-            FlakeRef(std::move(input), getOr(parsedURL.query, "dir", "")),
-            fragment);
+            return std::make_pair(
+                FlakeRef(std::move(input), getOr(parsedURL.query, "dir", "")),
+                fragment);
+        } catch (BadURL &) {
+            return parsePathFlakeRef();
+        }
     }
 }
 

src/libutil/tests/url.cc

@@ -335,4 +335,13 @@ namespace nix {
         ASSERT_EQ(d, s);
     }
 
+    TEST(percentEncode, yen) {
+        // https://en.wikipedia.org/wiki/Percent-encoding#Character_data
+        std::string s = reinterpret_cast<const char*>(u8"円");
+        std::string e = "%E5%86%86";
+
+        ASSERT_EQ(percentEncode(s), e);
+        ASSERT_EQ(percentDecode(e), s);
+    }
+
 }

src/libutil/url.cc

@@ -103,7 +103,7 @@ std::string percentEncode(std::string_view s, std::string_view keep)
             || keep.find(c) != std::string::npos)
             res += c;
         else
-            res += fmt("%%%02X", (unsigned int) c);
+            res += fmt("%%%02X", c & 0xFF);
     return res;
 }