Provide way for ui tests to opt out of having their output checked.

Namely, this adds support for:

 * `// dont-check-compiler-stdout`, and
 * `// dont-check-compiler-stderr`.

Obviously almost all ui tests wont want to opt into these, since the whole point
of a ui test is to check the compiler ui. However, since this PR is converting
run-pass into (another set of) ui tests, these header options make sense in that
context.

(Also this puts us into a better position for eventually turning
*every* test suite into a ui test suite, by making ui-ness the default
and forcing tests to opt out explicitly.)

src/tools/compiletest/src/header.rs

@@ -199,6 +199,10 @@ pub struct TestProps {
     pub force_host: bool,
     // Check stdout for error-pattern output as well as stderr
     pub check_stdout: 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
+    pub dont_check_compiler_stderr: bool,
     // Don't force a --crate-type=dylib flag on the command line
     pub no_prefer_dynamic: bool,
     // Run --pretty expanded when running pretty printing tests
@@ -249,6 +253,8 @@ pub fn new() -> Self {
             build_aux_docs: false,
             force_host: false,
             check_stdout: false,
+            dont_check_compiler_stdout: false,
+            dont_check_compiler_stderr: false,
             no_prefer_dynamic: false,
             pretty_expanded: false,
             pretty_mode: "normal".to_string(),
@@ -327,6 +333,14 @@ fn load_from(&mut self, testfile: &Path, cfg: Option<&str>, config: &Config) {
                 self.check_stdout = config.parse_check_stdout(ln);
             }
 
+            if !self.dont_check_compiler_stdout {
+                self.dont_check_compiler_stdout = config.parse_dont_check_compiler_stdout(ln);
+            }
+
+            if !self.dont_check_compiler_stderr {
+                self.dont_check_compiler_stderr = config.parse_dont_check_compiler_stderr(ln);
+            }
+
             if !self.no_prefer_dynamic {
                 self.no_prefer_dynamic = config.parse_no_prefer_dynamic(ln);
             }
@@ -510,6 +524,14 @@ fn parse_check_stdout(&self, line: &str) -> bool {
         self.parse_name_directive(line, "check-stdout")
     }
 
+    fn parse_dont_check_compiler_stdout(&self, line: &str) -> bool {
+        self.parse_name_directive(line, "dont-check-compiler-stdout")
+    }
+
+    fn parse_dont_check_compiler_stderr(&self, line: &str) -> bool {
+        self.parse_name_directive(line, "dont-check-compiler-stderr")
+    }
+
     fn parse_no_prefer_dynamic(&self, line: &str) -> bool {
         self.parse_name_directive(line, "no-prefer-dynamic")
     }

src/tools/compiletest/src/runtest.rs

@@ -2654,8 +2654,12 @@ fn run_ui_test(&self) {
         let normalized_stderr = self.normalize_output(&stderr, &self.props.normalize_stderr);
 
         let mut errors = 0;
-        errors += self.compare_output("stdout", &normalized_stdout, &expected_stdout);
-        errors += self.compare_output("stderr", &normalized_stderr, &expected_stderr);
+        if !self.props.dont_check_compiler_stdout {
+            errors += self.compare_output("stdout", &normalized_stdout, &expected_stdout);
+        }
+        if !self.props.dont_check_compiler_stderr {
+            errors += self.compare_output("stderr", &normalized_stderr, &expected_stderr);
+        }
 
         let modes_to_prune = vec![CompareMode::Nll];
         self.prune_duplicate_outputs(&modes_to_prune);