fix(#20456): detect enum type used as value at semantic stage

Add hasValidType() checks after resolveProperties() in visitIf,
visitFor, and visitDo (statementsem.d) so using an enum type name
as a boolean condition (e.g. 'if (Flags)') is caught during
semantic analysis instead of being deferred to e2ir/codegen, which
was silently skipped when compiling with -o-.

Fixes #20456

Author: usefahmed07

compiler/src/dmd/statementsem.d

@@ -658,6 +658,8 @@ Statement statementSemanticVisit(Statement s, Scope* sc)
 
         ds.condition = ds.condition.expressionSemantic(sc);
         ds.condition = resolveProperties(sc, ds.condition);
+        if (!ds.condition.hasValidType())
+            ds.condition = ErrorExp.get();
         if (checkNonAssignmentArrayOp(ds.condition))
             ds.condition = ErrorExp.get();
         ds.condition = ds.condition.optimize(WANTvalue);
@@ -730,6 +732,8 @@ Statement statementSemanticVisit(Statement s, Scope* sc)
 
             fs.condition = fs.condition.expressionSemantic(sc);
             fs.condition = resolveProperties(sc, fs.condition);
+            if (!fs.condition.hasValidType())
+                fs.condition = ErrorExp.get();
             if (checkNonAssignmentArrayOp(fs.condition))
                 fs.condition = ErrorExp.get();
             fs.condition = fs.condition.optimize(WANTvalue);
@@ -1798,6 +1802,8 @@ Statement statementSemanticVisit(Statement s, Scope* sc)
             ifs.condition = resolveProperties(scd, ifs.condition);
             ifs.condition = ifs.condition.addDtorHook(scd);
         }
+        if (!ifs.condition.hasValidType())
+            ifs.condition = ErrorExp.get();
         if (checkNonAssignmentArrayOp(ifs.condition))
             ifs.condition = ErrorExp.get();
 

compiler/test/fail_compilation/fail20456.d

@@ -0,0 +1,25 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/fail20456.d(14): Error: type `Flags` is not an expression
+fail_compilation/fail20456.d(19): Error: type `Flags` is not an expression
+fail_compilation/fail20456.d(24): Error: type `Flags` is not an expression
+---
+*/
+
+enum Flags : ubyte { Foo = 1, }
+
+void testIf()
+{
+    if (Flags) {}
+}
+
+void testWhile()
+{
+    while (Flags) {}
+}
+
+void testDoWhile()
+{
+    do {} while (Flags);
+}