Fix parsing logic of for loops' initial statement. (#5813)

Author: csyonghe

source/slang/slang-parser.cpp

@@ -5953,22 +5953,25 @@ ForStmt* Parser::ParseForStatement()
     FillPosition(stmt);
     ReadToken("for");
     ReadToken(TokenType::LParent);
-    auto modifiers = ParseModifiers(this);
-    if (peekTypeName(this) || !modifiers.isEmpty())
-    {
-        stmt->initialStatement = parseVarDeclrStatement(modifiers);
-    }
-    else
+    if (!LookAheadToken(TokenType::Semicolon))
     {
-        if (!LookAheadToken(TokenType::Semicolon))
+        stmt->initialStatement = ParseStatement();
+        if (as<DeclStmt>(stmt->initialStatement) || as<ExpressionStmt>(stmt->initialStatement))
         {
-            stmt->initialStatement = ParseExpressionStatement();
+            // These are the only allowed form of initial statements of a for loop.
         }
         else
         {
-            ReadToken(TokenType::Semicolon);
+            sink->diagnose(
+                stmt->initialStatement->loc,
+                Diagnostics::unexpectedTokenExpectedTokenType,
+                "expression");
         }
     }
+    else
+    {
+        ReadToken(TokenType::Semicolon);
+    }
     if (!LookAheadToken(TokenType::Semicolon))
         stmt->predicateExpression = ParseExpression();
     ReadToken(TokenType::Semicolon);

tests/language-feature/modules/typealias/lib.slang

@@ -0,0 +1,3 @@
+//TEST_IGNORE_FILE:
+
+typealias i32 = int32_t;

tests/language-feature/modules/typealias/main.slang

@@ -0,0 +1,24 @@
+//TEST:COMPARE_COMPUTE(filecheck-buffer=CHECK): -output-using-type
+
+// Regression test for bug https://github.com/shader-slang/slang/issues/5808
+
+// Using a type defined from a different module
+// in a for loop should work.
+
+import lib;
+
+//TEST_INPUT:set output = out ubuffer(data=[0 0 0 0], stride=4)
+RWStructuredBuffer<i32> output;
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+    // CHECK: 0
+    // CHECK: 1
+    // CHECK: 2
+    // CHECK: 3
+    for (i32 i = 0; i < 4; i++)
+    {
+        output[i] = i;
+    }
+}