From dccc9091c8f8f0911c79f7f6662c70c627249997 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Thu, 29 Jun 2023 13:11:49 -0700
Subject: Warn on semicolon after `if`. (#2948)

* Warn on semicolon after `if`.

* add test result

---------

Co-authored-by: Yong He <yhe@nvidia.com>
---
 source/slang/slang-parser.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

(limited to 'source/slang/slang-parser.cpp')

diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index d606698a1..dcf835234 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -184,7 +184,7 @@ namespace Slang
         void parseSourceFile(ModuleDecl* program);
         Decl* ParseStruct();
         ClassDecl* ParseClass();
-        Stmt* ParseStatement();
+        Stmt* ParseStatement(Stmt* parentStmt = nullptr);
         Stmt* parseBlockStatement();
         Stmt* parseLabelStatement();
         DeclStmt* parseVarDeclrStatement(Modifiers modifiers);
@@ -4438,7 +4438,7 @@ namespace Slang
         }
     }
 
-    Stmt* Parser::ParseStatement()
+    Stmt* Parser::ParseStatement(Stmt* parentStmt)
     {
         auto modifiers = ParseModifiers(this);
 
@@ -4575,6 +4575,13 @@ namespace Slang
         }
         else if (LookAheadToken(TokenType::Semicolon))
         {
+            if (as<IfStmt>(parentStmt))
+            {
+                // An empty statement after an `if` is probably a mistake,
+                // so we will diagnose it as such.
+                //
+                sink->diagnose(tokenReader.peekLoc(), Diagnostics::unintendedEmptyStatement);
+            }
             statement = astBuilder->create<EmptyStmt>();
             FillPosition(statement);
             ReadToken(TokenType::Semicolon);
@@ -4690,11 +4697,11 @@ namespace Slang
         ReadToken(TokenType::LParent);
         ifStatement->predicate = ParseExpression();
         ReadToken(TokenType::RParent);
-        ifStatement->positiveStatement = ParseStatement();
+        ifStatement->positiveStatement = ParseStatement(ifStatement);
         if (LookAheadToken("else"))
         {
             ReadToken("else");
-            ifStatement->negativeStatement = ParseStatement();
+            ifStatement->negativeStatement = ParseStatement(ifStatement);
         }
         return ifStatement;
     }
-- 
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