Propagate errors in for loop bodies

Closes #3819

src/ir.cpp

@@ -7456,6 +7456,8 @@ static IrInstruction *ir_gen_for_expr(IrBuilder *irb, Scope *parent_scope, AstNo
     // it's actually in break statements, handled similarly to return statements.
     // That is why we set those values in loop_scope above and not in this ir_gen_node call.
     IrInstruction *body_result = ir_gen_node(irb, body_node, &loop_scope->base);
+    if (body_result == irb->codegen->invalid_instruction)
+        return irb->codegen->invalid_instruction;
 
     if (!instr_is_unreachable(body_result)) {
         ir_mark_gen(ir_build_check_statement_is_void(irb, child_scope, node->data.for_expr.body, body_result));

test/compile_errors.zig

@@ -2,6 +2,15 @@ const tests = @import("tests.zig");
 const builtin = @import("builtin");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.addTest("errors in for loop bodies are propagated",
+        \\pub export fn entry() void {
+        \\    var arr: [100]u8 = undefined;
+        \\    for (arr) |bits| _ = @popCount(bits);
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:3:26: error: expected 2 arguments, found 1",
+    });
+
     cases.addTest("error in struct initializer doesn't crash the compiler",
         \\pub export fn entry() void {
         \\    const bitfield = struct {