fix: Solve bug when changing permissions with no modification right

libmamba/include/mamba/core/util.hpp

@@ -54,10 +54,12 @@ namespace mamba
 
     inline void make_executable(const fs::u8path& p)
     {
-        fs::permissions(
-            p,
-            fs::perms::owner_all | fs::perms::group_all | fs::perms::others_read | fs::perms::others_exec
-        );
+        const auto permissions = fs::perms::owner_all | fs::perms::group_all
+                                 | fs::perms::others_read | fs::perms::others_exec;
+        if (!fs::has_permissions(p, permissions))
+        {
+            fs::permissions(p, permissions);
+        }
     }
 
     // @return `true` if `TemporaryFile` will not delete files once destroy.

libmamba/include/mamba/fs/filesystem.hpp

@@ -1139,6 +1139,14 @@ namespace mamba::fs
         return std::filesystem::last_write_time(path, new_time, std::forward<OtherArgs>(args)...);
     }
 
+    /* Check if we have modification rights on a path.
+     * This function is not a wrapping on a of std::filesystem function, but it
+     * uses std::filesystem::status().
+     * Exceptions may be thrown by std::filesystem::status() if the path is not
+     * valid.
+     */
+    bool has_permissions(const u8path&, const fs::perms&);
+
     // void permissions(const path& p, perms prms, perm_options opts = perm_options::replace);
     // void permissions(const path& p, perms prms, error_code& ec) noexcept;
     // void permissions(const path& p, perms prms, perm_options opts, error_code& ec);

libmamba/src/core/subdir_index.cpp

@@ -1043,7 +1043,10 @@ namespace mamba
     auto create_cache_dir(const fs::u8path& cache_path) -> std::string
     {
         const auto cache_dir = cache_path / "cache";
-        fs::create_directories(cache_dir);
+        if (!std::filesystem::is_directory(cache_dir))
+        {
+            fs::create_directories(cache_dir);
+        }
 
         // Some filesystems don't support special permissions such as setgid on directories (e.g.
         // NFS). and fail if we try to set the setgid bit on the cache directory.
@@ -1056,20 +1059,27 @@ namespace mamba
 
         const auto permissions = fs::perms::owner_all | fs::perms::group_all
                                  | fs::perms::others_read | fs::perms::others_exec;
-        fs::permissions(cache_dir, permissions, fs::perm_options::replace);
-        LOG_TRACE << "Set permissions on cache directory " << cache_dir << " to 'rwxrwxr-x'";
-
-        std::error_code ec;
-        fs::permissions(cache_dir, fs::perms::set_gid, fs::perm_options::add, ec);
-
-        if (!ec)
+        if (!fs::has_permissions(cache_dir, permissions))
         {
-            LOG_TRACE << "Set setgid bit on cache directory " << cache_dir;
+            fs::permissions(cache_dir, permissions, fs::perm_options::replace);
+            LOG_TRACE << "Set permissions on cache directory " << cache_dir << " to 'rwxrwxr-x'";
         }
-        else
+
+        const auto setgid_perms = fs::perms::set_gid;
+        if (!fs::has_permissions(cache_dir, setgid_perms))
         {
-            LOG_TRACE << "Could not set setgid bit on cache directory " << cache_dir
-                      << "\nReason:" << ec.message() << "; ignoring and continuing";
+            std::error_code ec;
+            fs::permissions(cache_dir, setgid_perms, fs::perm_options::add, ec);
+
+            if (!ec)
+            {
+                LOG_TRACE << "Set setgid bit on cache directory " << cache_dir;
+            }
+            else
+            {
+                LOG_TRACE << "Could not set setgid bit on cache directory " << cache_dir
+                          << "\nReason:" << ec.message() << "; ignoring and continuing";
+            }
         }
 
         return cache_dir.string();

libmamba/src/fs/filesystem.cpp

@@ -12,7 +12,9 @@
 
 #ifndef _WIN32
 #include <fcntl.h>
+#include <pwd.h>
 #include <sys/stat.h>
+#include <unistd.h>
 // We can use the presence of UTIME_OMIT to detect platforms that provide
 // utimensat.
 #if defined(UTIME_OMIT)
@@ -79,4 +81,13 @@ namespace mamba::fs
         std::filesystem::last_write_time(path, new_time, ec);
 #endif
     }
+
+    bool has_permissions(const u8path& path, const fs::perms& perm)
+    {
+        // Get path permissions
+        auto p = std::filesystem::status(path).permissions();
+
+        // Path perms must include wanted perms
+        return perm == (p & perm);
+    }
 }

libmamba/tests/src/core/test_filesystem.cpp

@@ -452,4 +452,117 @@ namespace mamba
 
     }
 
+    namespace
+    {
+        TEST_CASE("has_permissions()")
+        {
+            // Create temp folder
+            const auto tmp_dir = fs::temp_directory_path() / "mamba-fs-has_permissions";
+            mamba::on_scope_exit _([&] { fs::remove_all(tmp_dir); });
+            fs::create_directories(tmp_dir);
+
+            // Create file
+            const auto some_file = tmp_dir / "some_file";
+            {
+                std::ofstream ofs{ some_file.std_path(),
+                                   std::ofstream::binary | std::ofstream::trunc };
+                ofs << "ABC" << std::endl;
+            }
+
+            // Set permissions
+            const auto perms = fs::perms::owner_read | fs::perms::owner_write | fs::perms::group_read;
+            fs::permissions(some_file, perms, fs::perm_options::replace);
+
+            // Check permissions
+            REQUIRE(fs::has_permissions(some_file, perms));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::owner_read));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::owner_write));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::group_read));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::owner_read | fs::perms::owner_write));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::owner_read | fs::perms::group_read));
+            REQUIRE(fs::has_permissions(some_file, fs::perms::owner_write | fs::perms::group_read));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::owner_exec));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::group_write));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::group_exec));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::others_read));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::others_write));
+            REQUIRE_FALSE(fs::has_permissions(some_file, fs::perms::others_exec));
+            REQUIRE_FALSE(
+                fs::has_permissions(some_file, fs::perms::owner_read | fs::perms::owner_exec)
+            );
+        }
+
+        // 2025-11-27 make_executable() bug
+        TEST_CASE(
+            "Bug: failure when calling make_executable()"
+            " on already executable file inside non-writable folder."
+        )
+        {
+            // Create temp folder
+            const auto tmp_dir = fs::temp_directory_path()
+                                 / "mamba-fs-make_executable-2025-11-27-bug";
+            mamba::on_scope_exit _([&] { fs::remove_all(tmp_dir); });
+            const auto folder = tmp_dir / "some_folder";
+            fs::create_directories(folder);
+
+            // Create file
+            const auto some_file = tmp_dir / "some_file";
+            {
+                std::ofstream ofs{ some_file.std_path(),
+                                   std::ofstream::binary | std::ofstream::trunc };
+                ofs << "ABC" << std::endl;
+            }
+
+            // Make executable
+            make_executable(some_file);
+
+            // Remove write permissions on parent folder
+            const auto perms = fs::perms::owner_read | fs::perms::owner_exec | fs::perms::group_read
+                               | fs::perms::group_exec | fs::perms::others_read
+                               | fs::perms::others_exec;
+            fs::permissions(folder, perms, fs::perm_options::replace);
+
+            // Make executable (again!)
+            // This should not fail
+            make_executable(some_file);
+
+            // Reset writing permission
+            const auto write_perms = fs::perms::owner_all;
+            fs::permissions(folder, write_perms, fs::perm_options::replace);
+        }
+
+        // 2025-11-27 create_cache_dir() bug
+        TEST_CASE(
+            "Bug: failure when calling create_cache_dir()"
+            " on already existing cache directory inside"
+            " non-writable folder."
+        )
+        {
+            // Create temp folder
+            const auto tmp_dir = fs::temp_directory_path()
+                                 / "mamba-fs-create_cache_dir-2025-11-27-bug";
+            mamba::on_scope_exit _([&] { fs::remove_all(tmp_dir); });
+            const auto folder = tmp_dir / "some_folder";
+            fs::create_directories(folder);
+
+            // Create cache folder
+            auto cache_dir = folder / "cache_dir";
+            create_cache_dir(cache_dir);
+
+            // Remove write permissions on parent folder
+            const auto perms = fs::perms::owner_read | fs::perms::owner_exec | fs::perms::group_read
+                               | fs::perms::group_exec | fs::perms::others_read
+                               | fs::perms::others_exec;
+            fs::permissions(folder, perms, fs::perm_options::replace);
+
+            // Create cache folder (again!)
+            // This should not fail
+            create_cache_dir(cache_dir);
+
+            // Reset writing permission
+            const auto write_perms = fs::perms::owner_all;
+            fs::permissions(folder, write_perms, fs::perm_options::replace);
+        }
+    }
+
 }