compiletest: Remove the libtest-based executor and its dependency

This patch has deliberately been kept small and simple, to make it easier to
revert if necessary. Further cleanup can take palce after we're confident that
it won't need to be reverted.

Author: Zalathar

src/bootstrap/src/core/build_steps/tool.rs

@@ -462,7 +462,7 @@ macro_rules! bootstrap_tool {
     }
 }
 
-pub(crate) const COMPILETEST_ALLOW_FEATURES: &str = "test,internal_output_capture";
+pub(crate) const COMPILETEST_ALLOW_FEATURES: &str = "internal_output_capture";
 
 bootstrap_tool!(
     // This is marked as an external tool because it includes dependencies

src/tools/compiletest/src/common.rs

@@ -413,14 +413,6 @@ pub struct Config {
     /// cross-compilation scenarios that do not otherwise want/need to `-Zbuild-std`. Used in e.g.
     /// ABI tests.
     pub minicore_path: Utf8PathBuf,
-
-    /// If true, disable the "new" executor, and use the older libtest-based
-    /// executor to run tests instead. This is a temporary fallback, to make
-    /// manual comparative testing easier if bugs are found in the new executor.
-    ///
-    /// FIXME(Zalathar): Eventually remove this flag and remove the libtest
-    /// dependency.
-    pub no_new_executor: bool,
 }
 
 impl Config {

src/tools/compiletest/src/executor.rs

@@ -12,7 +12,6 @@ use crate::common::{Config, TestPaths};
 
 mod deadline;
 mod json;
-pub(crate) mod libtest;
 
 pub(crate) fn run_tests(config: &Config, tests: Vec<CollectedTest>) -> bool {
     let tests_len = tests.len();

src/tools/compiletest/src/executor/libtest.rs

@@ -1,11 +1,10 @@
 #![crate_name = "compiletest"]
-// Needed by the libtest-based test executor.
-#![feature(test)]
 // Needed by the "new" test executor that does not depend on libtest.
+// FIXME(Zalathar): We should be able to get rid of `internal_output_capture`,
+// by having `runtest` manually capture all of its println-like output instead.
+// That would result in compiletest being written entirely in stable Rust!
 #![feature(internal_output_capture)]
 
-extern crate test;
-
 #[cfg(test)]
 mod tests;
 
@@ -448,8 +447,6 @@ pub fn parse_config(args: Vec<String>) -> Config {
         diff_command: matches.opt_str("compiletest-diff-tool"),
 
         minicore_path: opt_path(matches, "minicore-path"),
-
-        no_new_executor: matches.opt_present("no-new-executor"),
     }
 }
 
@@ -576,12 +573,10 @@ pub fn run_tests(config: Arc<Config>) {
     // Delegate to the executor to filter and run the big list of test structures
     // created during test discovery. When the executor decides to run a test,
     // it will return control to the rest of compiletest by calling `runtest::run`.
-    let res = if !config.no_new_executor {
-        Ok(executor::run_tests(&config, tests))
-    } else {
-        // FIXME(Zalathar): Eventually remove the libtest executor entirely.
-        crate::executor::libtest::execute_tests(&config, tests)
-    };
+    // FIXME(Zalathar): Once we're confident that we won't need to revert the
+    // removal of the libtest-based executor, remove this Result and other
+    // remnants of the old executor.
+    let res: io::Result<bool> = Ok(executor::run_tests(&config, tests));
 
     // Check the outcome reported by libtest.
     match res {