From 2671cda98f36467cca2202ee1e1b7764ed7efcd4 Mon Sep 17 00:00:00 2001
From: Pierre Tachoire <pierre@lightpanda.io>
Date: Mon, 25 Mar 2024 11:43:32 +0100
Subject: [PATCH] css: implement :lang match

---
 src/css/match_test.zig | 20 ++++++++++++++++++++
 src/css/selector.zig   | 19 ++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/css/match_test.zig b/src/css/match_test.zig
index 8e659043..47fbdb78 100644
--- a/src/css/match_test.zig
+++ b/src/css/match_test.zig
@@ -215,6 +215,16 @@ test "matchFirst" {
             .n = .{ .child = &.{ .name = "p", .child = &.{ .name = "a" }, .sibling = &.{ .name = "strong" } } },
             .exp = 0,
         },
+        .{
+            .q = "p:lang(en)",
+            .n = .{ .child = &.{ .name = "p", .att = "en-US", .child = &.{ .name = "a" } } },
+            .exp = 1,
+        },
+        .{
+            .q = "a:lang(en)",
+            .n = .{ .child = &.{ .name = "p", .child = &.{ .name = "a", .par = &.{ .att = "en-US" } } } },
+            .exp = 1,
+        },
     };
 
     for (testcases) |tc| {
@@ -379,6 +389,16 @@ test "matchAll" {
             .n = .{ .child = &.{ .name = "p", .child = &.{ .name = "a" }, .sibling = &.{ .name = "strong" } } },
             .exp = 0,
         },
+        .{
+            .q = "p:lang(en)",
+            .n = .{ .child = &.{ .name = "p", .att = "en-US", .child = &.{ .name = "a" } } },
+            .exp = 1,
+        },
+        .{
+            .q = "a:lang(en)",
+            .n = .{ .child = &.{ .name = "p", .child = &.{ .name = "a", .par = &.{ .att = "en-US" } } } },
+            .exp = 1,
+        },
     };
 
     for (testcases) |tc| {
diff --git a/src/css/selector.zig b/src/css/selector.zig
index a0c5d4d0..72485cac 100644
--- a/src/css/selector.zig
+++ b/src/css/selector.zig
@@ -337,11 +337,28 @@ pub const Selector = union(enum) {
                 }
             },
             .pseudo_class_only_child => |v| onlyChildMatch(v, n),
-            .pseudo_class_lang => return false,
+            .pseudo_class_lang => |v| langMatch(v, n),
             .pseudo_element => return false,
         };
     }
 
+    fn langMatch(lang: []const u8, n: anytype) anyerror!bool {
+        if (try n.attr("lang")) |own| {
+            if (std.mem.eql(u8, own, lang)) return true;
+
+            // check if the lang attr starts with lang+'-'
+            if (std.mem.startsWith(u8, own, lang)) {
+                if (own.len > lang.len and own[lang.len] == '-') return true;
+            }
+        }
+
+        // if the tag doesn't match, try the parent.
+        const p = try n.parent();
+        if (p == null) return false;
+
+        return langMatch(lang, p.?);
+    }
+
     // onlyChildMatch implements :only-child
     //  If `ofType` is true, it implements :only-of-type instead.
     fn onlyChildMatch(of_type: bool, n: anytype) anyerror!bool {