Rollup merge of #129837 - aDotInTheVoid:test-better-json, r=jieyouxu

Actually parse stdout json, instead of using hacky contains logic.

Fixes up the test added in #128963, to actually parse the stdout to JSON, instead of just checking that it contains `{"`.

CC ``@GuillaumeGomez``

r? ``@jieyouxu``

tests/run-make/rustdoc-output-stdout/rmake.rs

@@ -4,17 +4,28 @@
 use std::path::PathBuf;
 
 use run_make_support::path_helpers::{cwd, has_extension, read_dir_entries_recursive};
-use run_make_support::rustdoc;
+use run_make_support::{rustdoc, serde_json};
 
 fn main() {
- // First we check that we generate the JSON in the stdout.
- rustdoc()
+ let json_string = rustdoc()
  .input("foo.rs")
  .out_dir("-")
  .arg("-Zunstable-options")
  .output_format("json")
  .run()
- .assert_stdout_contains("{\"");
+ .stdout_utf8();
+
+ // First we check that we generate the JSON in the stdout.
+ let json_value: serde_json::Value =
+ serde_json::from_str(&json_string).expect("stdout should be valid json");
+
+ // We don't care to test the specifics of the JSON, as that's done
+ // elsewhere, just check that it has a format_version (as all JSON output
+ // should).
+ let format_version = json_value["format_version"]
+ .as_i64()
+ .expect("json output should contain format_version field");
+ assert!(format_version > 30);
 
  // Then we check it didn't generate any JSON file.
  read_dir_entries_recursive(cwd(), |path| {