From 85ea60b7f1121a95ffc2429d367ec211692cef16 Mon Sep 17 00:00:00 2001
From: Itamar <itamar8910@gmail.com>
Date: Fri, 26 Feb 2021 21:39:47 +0200
Subject: [PATCH] LibCpp: Don't fail when encountering #elif statements

However, we currently always treat the expression in #elif as true.
---
 Userland/Libraries/LibCpp/Preprocessor.cpp | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibCpp/Preprocessor.cpp b/Userland/Libraries/LibCpp/Preprocessor.cpp
index 3094d2b97c..99bef96ea3 100644
--- a/Userland/Libraries/LibCpp/Preprocessor.cpp
+++ b/Userland/Libraries/LibCpp/Preprocessor.cpp
@@ -81,7 +81,6 @@ void Preprocessor::handle_preprocessor_line(const StringView& line)
             m_state = State::Normal;
         }
         if (m_depths_of_taken_branches.contains_slow(m_current_depth - 1)) {
-            m_depths_of_taken_branches.contains_slow(m_current_depth - 1);
             m_state = State::SkipElseBranch;
         }
         return;
@@ -94,7 +93,7 @@ void Preprocessor::handle_preprocessor_line(const StringView& line)
             m_depths_of_not_taken_branches.remove_all_matching([this](auto x) { return x == m_current_depth; });
         }
         if (m_depths_of_taken_branches.contains_slow(m_current_depth)) {
-            m_depths_of_taken_branches.contains_slow(m_current_depth);
+            m_depths_of_taken_branches.remove_all_matching([this](auto x) { return x == m_current_depth; });
         }
         m_state = State::Normal;
         return;
@@ -159,6 +158,20 @@ void Preprocessor::handle_preprocessor_line(const StringView& line)
         }
         return;
     }
+
+    if (keyword == "elif") {
+        VERIFY(m_current_depth > 0);
+        // FIXME: Evaluate the elif expression
+        // We currently always treat the expression in #elif as true.
+        if (m_depths_of_not_taken_branches.contains_slow(m_current_depth - 1) /* && should_take*/) {
+            m_depths_of_not_taken_branches.remove_all_matching([this](auto x) { return x == m_current_depth - 1; });
+            m_state = State::Normal;
+        }
+        if (m_depths_of_taken_branches.contains_slow(m_current_depth - 1)) {
+            m_state = State::SkipElseBranch;
+        }
+        return;
+    }
     if (keyword == "pragma") {
         lexer.consume_all();
         return;