Sema: suggest using try/catch/if on method call on error union

src/Sema.zig

@@ -27888,6 +27888,9 @@ fn fieldCallBind(
             const decl = mod.declPtr(decl_idx);
             try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "'{}' is not a member function", .{field_name.fmt(ip)});
         }
+        if (concrete_ty.zigTypeTag(mod) == .ErrorUnion) {
+            try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
+        }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);

test/cases/compile_errors/method_call_on_error_union.zig

@@ -0,0 +1,21 @@
+const X = struct {
+    fn init() !X {
+        return error.a;
+    }
+
+    fn a(x: X) void {
+        _ = x;
+    }
+};
+
+export fn entry() void {
+    const x = X.init();
+    x.a();
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :13:6: error: no field or member function named 'a' in '@typeInfo(@typeInfo(@TypeOf(tmp.X.init)).Fn.return_type.?).ErrorUnion.error_set!tmp.X'
+// :13:6: note: consider using 'try', 'catch', or 'if'