Support relative and `~/` paths in config settings

Change-Id: I5566a9858ba255f4ac5051d1368c7dfb24460f0a

3 files changed, 35 insertions, 4 deletions

diff --git a/src/libutil/config.cc b/src/libutil/config.cc
index 333deb388..778da1413 100644
--- a/src/libutil/config.cc
+++ b/src/libutil/config.cc
@@ -126,7 +126,7 @@ static void applyConfigInner(const std::string & contents, const ApplyConfigOpti
             if (!options.path) {
                 throw UsageError("can only include configuration '%1%' from files", tokens[1]);
             }
-            auto pathToInclude = absPath(tokens[1], dirOf(*options.path));
+            auto pathToInclude = absPath(tildePath(tokens[1], options.home), dirOf(*options.path));
             if (pathExists(pathToInclude)) {
                 auto includeOptions = ApplyConfigOptions {
                     .path = pathToInclude,
@@ -437,10 +437,16 @@ template class BaseSetting<DeprecatedFeatures>;
 
 static Path parsePath(const AbstractSetting & s, const std::string & str, const ApplyConfigOptions & options)
 {
-    if (str == "")
+    if (str == "") {
         throw UsageError("setting '%s' is a path and paths cannot be empty", s.name);
-    else
-        return canonPath(str);
+    } else {
+        auto tildeResolvedPath = tildePath(str, options.home);
+        if (options.path) {
+            return absPath(tildeResolvedPath, dirOf(*options.path));
+        } else {
+            return canonPath(tildeResolvedPath);
+        }
+    }
 }
 
 template<> Path PathsSetting<Path>::parse(const std::string & str, const ApplyConfigOptions & options) const
diff --git a/src/libutil/file-system.cc b/src/libutil/file-system.cc
index 631cf076b..234c73163 100644
--- a/src/libutil/file-system.cc
+++ b/src/libutil/file-system.cc
@@ -117,6 +117,21 @@ Path realPath(Path const & path)
     return ret;
 }
 
+Path tildePath(Path const & path, const std::optional<Path> & home)
+{
+    if (path.starts_with("~/")) {
+        if (home) {
+            return *home + "/" + path.substr(2);
+        } else {
+            throw UsageError("`~` path not allowed: %1%", path);
+        }
+    } else if (path.starts_with('~')) {
+        throw UsageError("`~` paths must start with `~/`: %1%", path);
+    } else {
+        return path;
+    }
+}
+
 void chmodPath(const Path & path, mode_t mode)
 {
     if (chmod(path.c_str(), mode) == -1)
diff --git a/src/libutil/file-system.hh b/src/libutil/file-system.hh
index e49323e84..0a54d1a3b 100644
--- a/src/libutil/file-system.hh
+++ b/src/libutil/file-system.hh
@@ -63,6 +63,16 @@ Path canonPath(PathView path, bool resolveSymlinks = false);
 Path realPath(Path const & path);
 
 /**
+ * Resolve a tilde path like `~/puppy.nix` into an absolute path.
+ *
+ * If `home` is given, it's substituted for `~/` at the start of the input
+ * `path`. Otherwise, an error is thrown.
+ *
+ * If the path starts with `~` but not `~/`, an error is thrown.
+ */
+Path tildePath(Path const & path, const std::optional<Path> & home = std::nullopt);
+
+/**
  * Change the permissions of a path
  * Not called `chmod` as it shadows and could be confused with
  * `int chmod(char *, mode_t)`, which does not handle errors