Auto merge of #45944 - eddyb:provide, r=nikomatsakis

rustc_driver: expose a way to override query providers in CompileController.

This API has been a long-time coming and will probably become the main method for custom drivers (that is, binaries other than `rustc` itself that use `librustc_driver`) to adapt the compiler's behavior.

src/librustdoc/core.rs

@@ -154,9 +154,9 @@ pub fn run_core(search_paths: SearchPaths,
     target_features::add_configuration(&mut cfg, &sess);
     sess.parse_sess.config = cfg;
 
-    let krate = panictry!(driver::phase_1_parse_input(&driver::CompileController::basic(),
-                                                      &sess,
-                                                      &input));
+    let control = &driver::CompileController::basic();
+
+    let krate = panictry!(driver::phase_1_parse_input(control, &sess, &input));
     let krate = ReplaceBodyWithLoop::new().fold_crate(krate);
 
     let name = link::find_crate_name(Some(&sess), &krate.attrs, &input);
@@ -182,7 +182,8 @@ pub fn run_core(search_paths: SearchPaths,
                                                           &[],
                                                           &sess);
 
-    abort_on_err(driver::phase_3_run_analysis_passes(&sess,
+    abort_on_err(driver::phase_3_run_analysis_passes(control,
+                                                     &sess,
                                                      &*cstore,
                                                      hir_map,
                                                      analysis,