compiletest: Add support for //@ check-run-stdout-is-json-lines

Author: Zalathar

src/tools/compiletest/src/header.rs

@@ -129,6 +129,11 @@ pub struct TestProps {
     pub check_stdout: bool,
     // Check stdout & stderr for output of run-pass test
     pub check_run_results: bool,
+    /// Check that stdout from running the binary is legal JSON Lines
+    /// (i.e. each line is well-formed JSON).
+    ///
+    /// Has no effect in tests that don't run the compiled binary.
+    pub check_run_stdout_is_json_lines: bool,
     // For UI tests, allows compiler to generate arbitrary output to stdout
     pub dont_check_compiler_stdout: bool,
     // For UI tests, allows compiler to generate arbitrary output to stderr
@@ -226,6 +231,7 @@ mod directives {
     pub const FORCE_HOST: &'static str = "force-host";
     pub const CHECK_STDOUT: &'static str = "check-stdout";
     pub const CHECK_RUN_RESULTS: &'static str = "check-run-results";
+    pub const CHECK_RUN_STDOUT_IS_JSON_LINES: &'static str = "check-run-stdout-is-json-lines";
     pub const DONT_CHECK_COMPILER_STDOUT: &'static str = "dont-check-compiler-stdout";
     pub const DONT_CHECK_COMPILER_STDERR: &'static str = "dont-check-compiler-stderr";
     pub const NO_PREFER_DYNAMIC: &'static str = "no-prefer-dynamic";
@@ -285,6 +291,7 @@ impl TestProps {
             force_host: false,
             check_stdout: false,
             check_run_results: false,
+            check_run_stdout_is_json_lines: false,
             dont_check_compiler_stdout: false,
             dont_check_compiler_stderr: false,
             compare_output_lines_by_subset: false,
@@ -423,6 +430,11 @@ impl TestProps {
                         DONT_CHECK_COMPILER_STDOUT,
                         &mut self.dont_check_compiler_stdout,
                     );
+                    config.set_name_directive(
+                        ln,
+                        CHECK_RUN_STDOUT_IS_JSON_LINES,
+                        &mut self.check_run_stdout_is_json_lines,
+                    );
                     config.set_name_directive(
                         ln,
                         DONT_CHECK_COMPILER_STDERR,
@@ -739,6 +751,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "check-fail",
     "check-pass",
     "check-run-results",
+    "check-run-stdout-is-json-lines",
     "check-stdout",
     "check-test-line-numbers-match",
     "compare-output-lines-by-subset",

src/tools/compiletest/src/runtest.rs

@@ -3940,6 +3940,17 @@ impl<'test> TestCx<'test> {
                 self.fatal_proc_rec("test run succeeded!", &proc_res);
             }
 
+            if self.props.check_run_stdout_is_json_lines {
+                for (line, n) in proc_res.stdout.lines().zip(1..) {
+                    if serde_json::Value::from_str(line).is_err() {
+                        self.fatal_proc_rec(
+                            &format!("invalid JSON on line {n} of stdout: {line:?}"),
+                            &proc_res,
+                        );
+                    }
+                }
+            }
+
             if !self.props.error_patterns.is_empty() || !self.props.regex_error_patterns.is_empty()
             {
                 // "// error-pattern" comments

tests/ui/meta/check-run-stdout-is-json-lines.rs

@@ -0,0 +1,34 @@
+//@ run-pass
+//@ ignore-pass (JSON checks don't run under --check=pass)
+//@ check-run-stdout-is-json-lines
+
+//@ revisions: good bad_list bad_obj bad_empty bad_ws
+//@ [bad_list] should-fail
+//@ [bad_obj] should-fail
+//@ [bad_empty] should-fail
+//@ [bad_ws] should-fail
+
+// Check that `//@ check-run-stdout-is-json-lines` allows valid JSON lines and
+// rejects invalid JSON lines, even without `//@ check-run-results`.
+
+fn main() {
+    println!("true");
+    println!(r#"[ "this is valid json" ]"#);
+    println!(r#"{{ "key": "this is valid json" }}"#);
+
+    if cfg!(bad_list) {
+        println!(r#"[ "this is invalid json", ]"#);
+    }
+    if cfg!(bad_obj) {
+        println!(r#"{{ "key": "this is invalid json", }}"#);
+    }
+
+    // Every line must be valid JSON, and a blank or whitespace-only string is
+    // not valid JSON.
+    if cfg!(bad_empty) {
+        println!();
+    }
+    if cfg!(bad_ws) {
+        println!(" \t \t ");
+    }
+}