libutil: fix isInDir rejecting paths starting with dot

src/libutil-tests/file-system.cc

@@ -196,20 +196,42 @@ TEST(baseNameOf, absoluteNothingSlashNothing)
 
 TEST(isInDir, trivialCase)
 {
-    auto p1 = isInDir("/foo/bar", "/foo");
-    ASSERT_EQ(p1, true);
+    EXPECT_TRUE(isInDir("/foo/bar", "/foo"));
 }
 
 TEST(isInDir, notInDir)
 {
-    auto p1 = isInDir("/zes/foo/bar", "/foo");
-    ASSERT_EQ(p1, false);
+    EXPECT_FALSE(isInDir("/zes/foo/bar", "/foo"));
 }
 
 TEST(isInDir, emptyDir)
 {
-    auto p1 = isInDir("/zes/foo/bar", "");
-    ASSERT_EQ(p1, false);
+    EXPECT_FALSE(isInDir("/zes/foo/bar", ""));
+}
+
+TEST(isInDir, hiddenSubdirectory)
+{
+    EXPECT_TRUE(isInDir("/foo/.ssh", "/foo"));
+}
+
+TEST(isInDir, ellipsisEntry)
+{
+    EXPECT_TRUE(isInDir("/foo/...", "/foo"));
+}
+
+TEST(isInDir, sameDir)
+{
+    EXPECT_FALSE(isInDir("/foo", "/foo"));
+}
+
+TEST(isInDir, sameDirDot)
+{
+    EXPECT_FALSE(isInDir("/foo/.", "/foo"));
+}
+
+TEST(isInDir, dotDotPrefix)
+{
+    EXPECT_FALSE(isInDir("/foo/../bar", "/foo"));
 }
 
 /* ----------------------------------------------------------------------------

src/libutil/file-system.cc

@@ -183,9 +183,11 @@ bool isInDir(const std::filesystem::path & path, const std::filesystem::path & d
     /* Note that while the standard doesn't guarantee this, the
       `lexically_*` functions should do no IO and not throw. */
     auto rel = path.lexically_relative(dir);
-    /* Method from
-       https://stackoverflow.com/questions/62503197/check-if-path-contains-another-in-c++ */
-    return !rel.empty() && rel.native()[0] != OS_STR('.');
+    if (rel.empty())
+        return false;
+
+    auto first = *rel.begin();
+    return first != "." && first != "..";
 }
 
 bool isDirOrInDir(const std::filesystem::path & path, const std::filesystem::path & dir)