Coerce 'case' expressions to the same type as 'condition'

Some WGSL compilers complain if e.g. case expression is signed while
condition expression is unsigned.
Insert logic to coerce the case expression to be of the same type as the condition
expression.

This addresses issue shader-slang#4921.

source/slang/slang-check-stmt.cpp

@@ -299,7 +299,6 @@ namespace Slang
         // coerce to type being switch on, and ensure that value is a compile-time constant
         // The Vals in the AST are pointer-unique, making them easy to check for duplicates
         // by addeing them to a HashSet.
-        auto exprVal = tryConstantFoldExpr(expr, ConstantFoldingKind::CompileTime, nullptr);
         auto switchStmt = FindOuterStmt<SwitchStmt>();
 
         if (!switchStmt)
@@ -308,9 +307,13 @@ namespace Slang
         }
         else
         {
-            // TODO: need to do some basic matching to ensure the type
-            // for the `case` is consistent with the type for the `switch`...
+            // Try to coerce the case expression to the same type as the condition
+            Expr* condition = switchStmt->condition;
+            expr = coerce(CoercionSite::General, condition->type, expr);
+            // Can't think of any cases where this would fail
+            SLANG_ASSERT(expr);
         }
+        auto exprVal = tryConstantFoldExpr(expr, ConstantFoldingKind::CompileTime, nullptr);
 
         stmt->expr = expr;
         stmt->exprVal = exprVal;