AWS S3 binary cache miss should not issue warning

src/vcpkg/binarycaching.cpp

@@ -1128,7 +1128,21 @@ namespace
                 cmd.string_arg("--no-sign-request");
             }
 
-            return flatten(cmd_execute_and_capture_output(cmd), Tools::AWSCLI).map(unit_to_cache_hit);
+            auto maybe_exit = cmd_execute_and_capture_output(cmd);
+            // When the file is not found, "aws s3 ls" prints nothing, and returns exit code 1.
+            // flatten() would treat this as an error, but we want to treat it as a (silent) cache miss instead.
+            // See https://github.com/aws/aws-cli/issues/5544 for the related aws-cli bug report.
+            if (auto exit = maybe_exit.get())
+            {
+                // We want to return CacheResult::miss even if aws-cli starts to return success
+                const bool success_or_exit_code_1 = exit->exit_code == 0 || exit->exit_code == 1;
+                const bool output_is_empty = Strings::trim(exit->output) == "";
+                if (success_or_exit_code_1 && output_is_empty)
+                {
+                    return CacheResult::miss;
+                }
+            }
+            return flatten(maybe_exit, Tools::AWSCLI).map(unit_to_cache_hit);
         }
 
         ExpectedL<CacheResult> download_file(StringView object, const Path& archive) const override