From 25cfa6716aa2242c9744cbcac49c37e3f45e1eb8 Mon Sep 17 00:00:00 2001
From: Valentin Gagarin <valentin.gagarin@tweag.io>
Date: Wed, 27 Nov 2024 12:51:38 +0100
Subject: [PATCH] fix relative path computation

---
 website/lib.nix   | 22 +++++++++++-----------
 website/tests.nix | 18 ++++++++++++++----
 2 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/website/lib.nix b/website/lib.nix
index 6dcff3a0..9485d46b 100644
--- a/website/lib.nix
+++ b/website/lib.nix
@@ -99,22 +99,22 @@ rec {
   relativePath = path1': path2':
     let
       inherit (lib.path) subpath;
-      inherit (lib) lists;
+      inherit (lib) lists length take drop min max;
+      inherit (lists) replicate findFirstIndex zipLists;
 
       path1 = subpath.components path1';
-      prefix1 = with lib; take (length path1 - 1) path1;
       path2 = subpath.components path2';
-      prefix2 = with lib; take (length path2 - 1) path2;
+      prefix1 = take (length path1 - 1) path1;
 
-      commonPrefixLength = with lists;
-        findFirstIndex (i: i.fst != i.snd)
-          (length prefix1)
-          (zipLists prefix1 prefix2);
-
-      relativeComponents = with lists;
-        [ "." ] ++ (replicate (length prefix1 - commonPrefixLength) "..") ++ (drop commonPrefixLength path2);
+      common-prefix-length = findFirstIndex (i: i.fst != i.snd)
+        (min (length prefix1) (length path2 - 1))
+        (zipLists prefix1 path2);
+      parent-levels = max 0 (length prefix1 - common-prefix-length);
+      relative-components = [ "." ] ++
+        (replicate parent-levels "..") ++
+        (drop common-prefix-length path2);
     in
-    join "/" relativeComponents;
+    join "/" relative-components;
 
   /**
     Recursively list all Nix files from a directory, except the top-level `default.nix`
diff --git a/website/tests.nix b/website/tests.nix
index 5fe31b60..58184a78 100644
--- a/website/tests.nix
+++ b/website/tests.nix
@@ -4,8 +4,18 @@ let
   inherit (import ./. { }) lib;
 in
 {
-  test-relativePath = {
-    expr = with lib; relativePath "bar" "baz";
-    expected = "./baz";
-  };
+  test-relativePath = with lib;
+    let
+      testData = [
+        { from = "bar"; to = "baz"; expected = "./baz"; }
+        { from = "foo/bar"; to = "foo/baz"; expected = "./baz"; }
+        { from = "foo"; to = "bar/baz"; expected = "./bar/baz"; }
+        { from = "foo/bar"; to = "baz"; expected = "./../baz"; }
+        { from = "foo/bar/baz"; to = "foo"; expected = "./../../foo"; }
+      ];
+    in
+    {
+      expr = map (case: relativePath case.from case.to) testData;
+      expected = map (case: case.expected) testData;
+    };
 }