Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libutil/url.hh

@@ -0,0 +1,69 @@
+#pragma once
+///@file
+
+#include "error.hh"
+
+namespace nix {
+
+struct ParsedURL
+{
+    std::string url;
+    /// URL without query/fragment
+    std::string base;
+    std::string scheme;
+    std::optional<std::string> authority;
+    std::string path;
+    std::map<std::string, std::string> query;
+    std::string fragment;
+
+    std::string to_string() const;
+
+    bool operator ==(const ParsedURL & other) const noexcept;
+
+    /**
+     * Remove `.` and `..` path elements.
+     */
+    ParsedURL canonicalise();
+};
+
+MakeError(BadURL, Error);
+
+std::string percentDecode(std::string_view in);
+std::string percentEncode(std::string_view s, std::string_view keep="");
+
+std::map<std::string, std::string> decodeQuery(const std::string & query);
+
+std::string encodeQuery(const std::map<std::string, std::string> & query);
+
+ParsedURL parseURL(const std::string & url);
+
+/**
+ * Although that’s not really standardized anywhere, an number of tools
+ * use a scheme of the form 'x+y' in urls, where y is the “transport layer”
+ * scheme, and x is the “application layer” scheme.
+ *
+ * For example git uses `git+https` to designate remotes using a Git
+ * protocol over http.
+ */
+struct ParsedUrlScheme {
+    std::optional<std::string_view> application;
+    std::string_view transport;
+};
+
+ParsedUrlScheme parseUrlScheme(std::string_view scheme);
+
+/* Detects scp-style uris (e.g. git@github.com:NixOS/nix) and fixes
+   them by removing the `:` and assuming a scheme of `ssh://`. Also
+   changes absolute paths into file:// URLs. */
+std::string fixGitURL(const std::string & url);
+
+/**
+ * Whether a string is valid as RFC 3986 scheme name.
+ * Colon `:` is part of the URI; not the scheme name, and therefore rejected.
+ * See https://www.rfc-editor.org/rfc/rfc3986#section-3.1
+ *
+ * Does not check whether the scheme is understood, as that's context-dependent.
+ */
+bool isValidSchemeName(std::string_view scheme);
+
+}