From f28b7064ee6785e26b8ac3097c3a11e56aa30df0 Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@ladybird.org>
Date: Fri, 1 Aug 2025 11:33:53 +0200
Subject: [PATCH] LibWeb: Add indentation to display list dumps

Output display list dumps with an indentation level to show balanced
commands. It makes it much easier to see what is happening between e.g.
PushStackingContext and PopStackingContext, or SaveLayer and Restore.
---
 Libraries/LibWeb/Painting/DisplayList.cpp     | 25 ++++++++++++++++---
 .../LibWeb/Painting/DisplayListCommand.h      | 16 ++++++++++++
 .../LibWeb/Painting/DisplayListRecorder.cpp   |  2 +-
 .../display_list/simple-overflow-hidden.txt   | 14 +++++------
 4 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/Libraries/LibWeb/Painting/DisplayList.cpp b/Libraries/LibWeb/Painting/DisplayList.cpp
index f0664151df0..254a3ee3563 100644
--- a/Libraries/LibWeb/Painting/DisplayList.cpp
+++ b/Libraries/LibWeb/Painting/DisplayList.cpp
@@ -18,9 +18,28 @@ void DisplayList::append(DisplayListCommand&& command, Optional<i32> scroll_fram
 String DisplayList::dump() const
 {
     StringBuilder builder;
-    for (auto const& command : m_commands) {
-        command.command.visit([&builder](auto const& cmd) { cmd.dump(builder); });
-        builder.appendff("\n");
+    int indentation = 0;
+    for (auto const& command_list_item : m_commands) {
+        auto const& command = command_list_item.command;
+
+        command.visit([&indentation](auto const& command) {
+            if constexpr (requires { command.nesting_level_change; }) {
+                if (command.nesting_level_change < 0 && indentation >= -command.nesting_level_change)
+                    indentation += command.nesting_level_change;
+            }
+        });
+
+        if (indentation > 0)
+            builder.append(MUST(String::repeated("  "_string, indentation)));
+        command.visit([&builder](auto const& cmd) { cmd.dump(builder); });
+        builder.append('\n');
+
+        command.visit([&indentation](auto const& command) {
+            if constexpr (requires { command.nesting_level_change; }) {
+                if (command.nesting_level_change > 0)
+                    indentation += command.nesting_level_change;
+            }
+        });
     }
     return builder.to_string_without_validation();
 }
diff --git a/Libraries/LibWeb/Painting/DisplayListCommand.h b/Libraries/LibWeb/Painting/DisplayListCommand.h
index ad0f925feea..29e85b96eee 100644
--- a/Libraries/LibWeb/Painting/DisplayListCommand.h
+++ b/Libraries/LibWeb/Painting/DisplayListCommand.h
@@ -99,14 +99,20 @@ struct DrawRepeatedImmutableBitmap {
 };
 
 struct Save {
+    static constexpr int nesting_level_change = 1;
+
     void dump(StringBuilder&) const;
 };
 
 struct SaveLayer {
+    static constexpr int nesting_level_change = 1;
+
     void dump(StringBuilder&) const;
 };
 
 struct Restore {
+    static constexpr int nesting_level_change = -1;
+
     void dump(StringBuilder&) const;
 };
 
@@ -127,6 +133,8 @@ struct AddClipRect {
 };
 
 struct PushStackingContext {
+    static constexpr int nesting_level_change = 1;
+
     float opacity;
     Gfx::CompositingAndBlendingOperator compositing_and_blending_operator;
     bool isolate;
@@ -145,6 +153,8 @@ struct PushStackingContext {
 };
 
 struct PopStackingContext {
+    static constexpr int nesting_level_change = -1;
+
     void dump(StringBuilder&) const;
 };
 
@@ -445,16 +455,22 @@ struct PaintScrollBar {
 };
 
 struct ApplyOpacity {
+    static constexpr int nesting_level_change = 1;
+
     float opacity;
     void dump(StringBuilder&) const;
 };
 
 struct ApplyCompositeAndBlendingOperator {
+    static constexpr int nesting_level_change = 1;
+
     Gfx::CompositingAndBlendingOperator compositing_and_blending_operator;
     void dump(StringBuilder&) const;
 };
 
 struct ApplyFilter {
+    static constexpr int nesting_level_change = 1;
+
     Gfx::Filter filter;
     void dump(StringBuilder&) const;
 };
diff --git a/Libraries/LibWeb/Painting/DisplayListRecorder.cpp b/Libraries/LibWeb/Painting/DisplayListRecorder.cpp
index 2e376dcb13d..859e9724f68 100644
--- a/Libraries/LibWeb/Painting/DisplayListRecorder.cpp
+++ b/Libraries/LibWeb/Painting/DisplayListRecorder.cpp
@@ -462,7 +462,7 @@ void DisplayListRecorder::apply_opacity(float opacity)
 void DisplayListRecorder::apply_compositing_and_blending_operator(Gfx::CompositingAndBlendingOperator compositing_and_blending_operator)
 {
     // Implementation of this item does saveLayer(), so we need to increment the nesting level.
-    m_save_nesting_level++;
+    ++m_save_nesting_level;
     APPEND(ApplyCompositeAndBlendingOperator { .compositing_and_blending_operator = compositing_and_blending_operator });
 }
 
diff --git a/Tests/LibWeb/Text/expected/display_list/simple-overflow-hidden.txt b/Tests/LibWeb/Text/expected/display_list/simple-overflow-hidden.txt
index e1ac6f5d6ee..a0182d2faff 100644
--- a/Tests/LibWeb/Text/expected/display_list/simple-overflow-hidden.txt
+++ b/Tests/LibWeb/Text/expected/display_list/simple-overflow-hidden.txt
@@ -1,10 +1,10 @@
 SaveLayer
-PushStackingContext opacity=1 isolate=false has_clip_path=false transform=[1 0 0 1 0 0]
-PushStackingContext opacity=1 isolate=false has_clip_path=false transform=[1 0 0 1 0 0]
-FillPathUsingColor
-FillRect rect=[10,10 300x150] color=rgb(240, 128, 128)
-DrawGlyphRun rect=[10,10 38x18] translation=[10,23.796875] color=rgb(0, 0, 0) scale=1
-PopStackingContext
-PopStackingContext
+  PushStackingContext opacity=1 isolate=false has_clip_path=false transform=[1 0 0 1 0 0]
+    PushStackingContext opacity=1 isolate=false has_clip_path=false transform=[1 0 0 1 0 0]
+      FillPathUsingColor
+      FillRect rect=[10,10 300x150] color=rgb(240, 128, 128)
+      DrawGlyphRun rect=[10,10 38x18] translation=[10,23.796875] color=rgb(0, 0, 0) scale=1
+    PopStackingContext
+  PopStackingContext
 Restore