Fix ICE with continue/break/return in while condition,Fixes #3977

Author: Harishankar14

gcc/rust/typecheck/rust-hir-type-check-expr.cc

@@ -1550,18 +1550,46 @@ void
 TypeCheckExpr::visit (HIR::WhileLoopExpr &expr)
 {
   context->push_new_while_loop_context (expr.get_mappings ().get_hirid ());
-
-  TypeCheckExpr::Resolve (expr.get_predicate_expr ());
+  TyTy::BaseType *predicate_type
+    = TypeCheckExpr::Resolve (expr.get_predicate_expr ());
+  if (predicate_type->get_kind () == TyTy::TypeKind::ERROR)
+    {
+      infered = TyTy::TupleType::get_unit_type ();
+      context->pop_loop_context ();
+      return;
+    }
+  if (predicate_type->get_kind () == TyTy::TypeKind::NEVER)
+    {
+      rust_error_at (expr.get_predicate_expr ().get_locus (),
+		     "expected boolean expression in %<while%> condition");
+      infered = TyTy::TupleType::get_unit_type ();
+      context->pop_loop_context ();
+      return;
+    }
+  if (predicate_type->get_kind () != TyTy::TypeKind::BOOL)
+    {
+      rust_error_at (expr.get_predicate_expr ().get_locus (),
+		     "expected boolean expression in %<while%> condition");
+      infered = TyTy::TupleType::get_unit_type ();
+      context->pop_loop_context ();
+      return;
+    }
   TyTy::BaseType *block_expr = TypeCheckExpr::Resolve (expr.get_loop_block ());
-
   if (!block_expr->is_unit ())
     {
       rust_error_at (expr.get_loop_block ().get_locus (),
 		     "expected %<()%> got %s",
 		     block_expr->as_string ().c_str ());
+      infered = TyTy::TupleType::get_unit_type ();
+      context->pop_loop_context ();
+      return;
+    }
+  if (block_expr->get_kind () == TyTy::TypeKind::ERROR)
+    {
+      infered = TyTy::TupleType::get_unit_type ();
+      context->pop_loop_context ();
       return;
     }
-
   context->pop_loop_context ();
   infered = TyTy::TupleType::get_unit_type ();
 }

gcc/testsuite/rust/compile/issue-3977.rs

@@ -0,0 +1,72 @@
+// Test for issue #3977: ICE in fold_convert_loc with diverging expressions in while conditions
+// { dg-excess-errors "expected boolean expression" }
+
+fn test_continue() {
+    loop {
+        while continue {} // { dg-error "expected boolean expression in 'while' condition" }
+    }
+}
+
+fn test_break() {
+    loop {
+        while break {} // { dg-error "expected boolean expression in 'while' condition" }
+    }
+}
+
+fn test_return() {
+    while return {} // { dg-error "expected boolean expression in 'while' condition" }
+}
+
+fn test_return_with_value() {
+    while return 42 {} // { dg-error "expected boolean expression in 'while' condition" }
+}
+
+fn test_infinite_loop() {
+    while loop {} {} // { dg-error "expected boolean expression in 'while' condition" }
+}
+
+fn test_nested_continue() {
+    loop {
+        loop {
+            while continue {} // { dg-error "expected boolean expression in 'while' condition" }
+        }
+    }
+}
+
+fn test_labeled_break() {
+    'outer: loop {
+        while break 'outer {} // { dg-error "expected boolean expression in 'while' condition" }
+    }
+}
+
+fn test_labeled_continue() {
+    'outer: loop {
+        while continue 'outer {} // { dg-error "expected boolean expression in 'while' condition" }
+    }
+}
+
+// Valid cases that should NOT error
+fn test_valid_boolean() {
+    while true {}
+    while false {}
+}
+
+fn test_valid_expression() {
+    let x = 5;
+    while x > 0 {}
+}
+
+fn test_valid_function_call() -> bool {
+    fn condition() -> bool { true }
+    while condition() {}
+    true
+}
+
+fn main() {
+    test_valid_boolean();
+    test_valid_expression();
+    test_valid_function_call();
+    
+    // The error cases would cause compilation to fail
+    // so they're tested separately
+}