From 5078a63084121fa31d6d763dfa30ba5b0f99f040 Mon Sep 17 00:00:00 2001
From: Jordan Woyak <jordan.woyak@gmail.com>
Date: Wed, 6 Nov 2024 19:13:33 -0600
Subject: [PATCH] InputCommon: Add ternary conditional operator to input
 expressions.

---
 .../DolphinQt/Config/Mapping/IOWindow.cpp     |  3 +
 .../ControlReference/ExpressionParser.cpp     | 60 +++++++++++++++----
 .../ControlReference/ExpressionParser.h       |  2 +
 3 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp b/Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp
index 9c9dc3e3b6..a43d91df09 100644
--- a/Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp
+++ b/Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp
@@ -160,6 +160,8 @@ void ControlExpressionSyntaxHighlighter::highlightBlock(const QString&)
     case TokenType::TOK_LPAREN:
     case TokenType::TOK_RPAREN:
     case TokenType::TOK_COMMA:
+    case TokenType::TOK_QUESTION:
+    case TokenType::TOK_COLON:
       char_format = GetSpecialCharFormat();
       break;
     case TokenType::TOK_LITERAL:
@@ -290,6 +292,7 @@ void IOWindow::CreateMainLayout()
     m_operators_combo->addItem(tr("< Less-than"));
     m_operators_combo->addItem(tr("& And"));
     m_operators_combo->addItem(tr("^ Xor"));
+    m_operators_combo->addItem(tr("? Conditional"));
   }
   m_operators_combo->addItem(tr("| Or"));
   m_operators_combo->addItem(tr("$ User Variable"));
diff --git a/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp b/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
index b558d6b78f..e256eeeff5 100644
--- a/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
+++ b/Source/Core/InputCommon/ControlReference/ExpressionParser.cpp
@@ -168,6 +168,10 @@ Token Lexer::NextToken()
     return Token(TOK_RPAREN);
   case '@':
     return Token(TOK_HOTKEY);
+  case '?':
+    return Token(TOK_QUESTION);
+  case ':':
+    return Token(TOK_COLON);
   case '&':
     return Token(TOK_AND);
   case '|':
@@ -745,7 +749,7 @@ private:
         {
           // Read one argument.
           // Grab an expression, but stop at comma.
-          auto arg = ParseBinary(BinaryOperatorPrecedence(TOK_COMMA));
+          auto arg = ParseInfixOperations(OperatorPrecedence(TOK_COMMA));
           if (ParseStatus::Successful != arg.status)
             return arg;
 
@@ -844,7 +848,7 @@ private:
     }
   }
 
-  static int BinaryOperatorPrecedence(TokenType type)
+  static constexpr int OperatorPrecedence(TokenType type = TOK_EOF)
   {
     switch (type)
     {
@@ -865,16 +869,16 @@ private:
     case TOK_OR:
       return 6;
     case TOK_ASSIGN:
+    case TOK_QUESTION:
       return 7;
     case TOK_COMMA:
       return 8;
     default:
-      ASSERT(false);
-      return 0;
+      return 999;
     }
   }
 
-  ParseResult ParseBinary(int precedence = 999)
+  ParseResult ParseInfixOperations(int precedence = OperatorPrecedence())
   {
     ParseResult lhs = ParseAtom(Chew());
 
@@ -884,18 +888,48 @@ private:
     std::unique_ptr<Expression> expr = std::move(lhs.expr);
 
     // TODO: handle LTR/RTL associativity?
-    while (Peek().IsBinaryOperator() && BinaryOperatorPrecedence(Peek().type) < precedence)
+    while (true)
     {
-      const Token tok = Chew();
-      ParseResult rhs = ParseBinary(BinaryOperatorPrecedence(tok.type));
-      if (rhs.status == ParseStatus::SyntaxError)
+      const Token op = Peek();
+      if (op.IsBinaryOperator() && OperatorPrecedence(op.type) < precedence)
       {
-        return rhs;
+        Chew();
+        ParseResult rhs = ParseInfixOperations(OperatorPrecedence(op.type));
+        if (rhs.status == ParseStatus::SyntaxError)
+          return rhs;
+
+        expr = std::make_unique<BinaryExpression>(op.type, std::move(expr), std::move(rhs.expr));
       }
+      else if (op.type == TOK_QUESTION && OperatorPrecedence(TOK_QUESTION) <= precedence)
+      {
+        // Handle conditional operator: (a ? b : c)
+        Chew();
+        auto true_result = ParseInfixOperations(OperatorPrecedence(op.type));
+        if (true_result.status != ParseStatus::Successful)
+          return true_result;
 
-      expr = std::make_unique<BinaryExpression>(tok.type, std::move(expr), std::move(rhs.expr));
+        const Token should_be_colon = Chew();
+        if (should_be_colon.type != TOK_COLON)
+          return ParseResult::MakeErrorResult(should_be_colon,
+                                              Common::GetStringT("Expected colon."));
+
+        auto false_result = ParseInfixOperations(OperatorPrecedence(op.type));
+        if (false_result.status != ParseStatus::Successful)
+          return false_result;
+
+        auto conditional = MakeFunctionExpression("if");
+        std::vector<std::unique_ptr<Expression>> args;
+        args.emplace_back(std::move(expr));
+        args.emplace_back(std::move(true_result.expr));
+        args.emplace_back(std::move(false_result.expr));
+        conditional->SetArguments(std::move(args));
+        expr = std::move(conditional);
+      }
+      else
+      {
+        break;
+      }
     }
-
     return ParseResult::MakeSuccessfulResult(std::move(expr));
   }
 
@@ -948,7 +982,7 @@ private:
     return ParseResult::MakeSuccessfulResult(std::make_unique<HotkeyExpression>(std::move(inputs)));
   }
 
-  ParseResult ParseToplevel() { return ParseBinary(); }
+  ParseResult ParseToplevel() { return ParseInfixOperations(); }
 };  // namespace ExpressionParser
 
 ParseResult ParseTokens(const std::vector<Token>& tokens)
diff --git a/Source/Core/InputCommon/ControlReference/ExpressionParser.h b/Source/Core/InputCommon/ControlReference/ExpressionParser.h
index bc39762127..4952915ced 100644
--- a/Source/Core/InputCommon/ControlReference/ExpressionParser.h
+++ b/Source/Core/InputCommon/ControlReference/ExpressionParser.h
@@ -26,6 +26,8 @@ enum TokenType
   TOK_BAREWORD,
   TOK_COMMENT,
   TOK_HOTKEY,
+  TOK_QUESTION,
+  TOK_COLON,
   // Binary Ops:
   TOK_BINARY_OPS_BEGIN,
   TOK_AND = TOK_BINARY_OPS_BEGIN,