Use `std.fs.path.relative` for `@import` and `@embedFile` sub paths

Fixes edge cases where the `startsWith` that was used previously would return a false positive on a resolved path like `foo.zig` when the resolved root was `foo`. Before this commit, such a path would be treated as a sub path of 'foo' with a resolved sub file path of 'zig' (and the `.` would be assumed to be a path separator). After this commit, `foo.zig` will be correctly treated as outside of the root of `foo`.

Closes #18355

1 files changed, 10 insertions, 18 deletions

diff --git a/src/Module.zig b/src/Module.zig
index 9d3810f671..cac4543883 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -3939,15 +3939,11 @@ pub fn importFile(
     defer gpa.free(resolved_root_path);
 
     const sub_file_path = p: {
-        if (mem.startsWith(u8, resolved_path, resolved_root_path)) {
-            // +1 for the directory separator here.
-            break :p try gpa.dupe(u8, resolved_path[resolved_root_path.len + 1 ..]);
-        }
-        if (mem.eql(u8, resolved_root_path, ".") and
-            !isUpDir(resolved_path) and
-            !std.fs.path.isAbsolute(resolved_path))
-        {
-            break :p try gpa.dupe(u8, resolved_path);
+        const relative = try std.fs.path.relative(gpa, resolved_root_path, resolved_path);
+        errdefer gpa.free(relative);
+
+        if (!isUpDir(relative) and !std.fs.path.isAbsolute(relative)) {
+            break :p relative;
         }
         return error.ImportOutsideModulePath;
     };
@@ -4038,15 +4034,11 @@ pub fn embedFile(
     defer gpa.free(resolved_root_path);
 
     const sub_file_path = p: {
-        if (mem.startsWith(u8, resolved_path, resolved_root_path)) {
-            // +1 for the directory separator here.
-            break :p try gpa.dupe(u8, resolved_path[resolved_root_path.len + 1 ..]);
-        }
-        if (mem.eql(u8, resolved_root_path, ".") and
-            !isUpDir(resolved_path) and
-            !std.fs.path.isAbsolute(resolved_path))
-        {
-            break :p try gpa.dupe(u8, resolved_path);
+        const relative = try std.fs.path.relative(gpa, resolved_root_path, resolved_path);
+        errdefer gpa.free(relative);
+
+        if (!isUpDir(relative) and !std.fs.path.isAbsolute(relative)) {
+            break :p relative;
         }
         return error.ImportOutsideModulePath;
     };