Auto merge of #46106 - est31:master, r=nikomatsakis

Add a MIR-borrowck-only output mode

Removes the `-Z borrowck-mir` flag in favour of a `-Z borrowck=mode` flag where mode can be `mir`, `ast`, or `compare`.

* The `ast` mode represents the current default, passing `-Z borrowck=ast` is equivalent to not passing it at all.
* The `compare` mode outputs both the output of the MIR borrow checker and the AST borrow checker, each error with `(Ast)` and `(Mir)` appended. This mode has the same behaviour as `-Z borrowck-mir` had before this commit.
* The `mir` mode only outputs the results of the MIR borrow checker, while suppressing the errors of the ast borrow checker

The PR also updates the tests to use the new flags.

closes  #46097

src/librustc/session/config.rs

@@ -362,6 +362,9 @@ top_level_options!(
 
         debugging_opts: DebuggingOptions [TRACKED],
         prints: Vec<PrintRequest> [UNTRACKED],
+        // Determines which borrow checker(s) to run. This is the parsed, sanitized
+        // version of `debugging_opts.borrowck`, which is just a plain string.
+        borrowck_mode: BorrowckMode [UNTRACKED],
         cg: CodegenOptions [TRACKED],
         // FIXME(mw): We track this for now but it actually doesn't make too
         //            much sense: The value of this option can stay the same
@@ -401,6 +404,32 @@ pub enum PrintRequest {
     NativeStaticLibs,
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum BorrowckMode {
+    Ast,
+    Mir,
+    Compare,
+}
+
+impl BorrowckMode {
+    /// Should we emit the AST-based borrow checker errors?
+    pub fn use_ast(self) -> bool {
+        match self {
+            BorrowckMode::Ast => true,
+            BorrowckMode::Compare => true,
+            BorrowckMode::Mir => false,
+        }
+    }
+    /// Should we emit the MIR-based borrow checker errors?
+    pub fn use_mir(self) -> bool {
+        match self {
+            BorrowckMode::Ast => false,
+            BorrowckMode::Compare => true,
+            BorrowckMode::Mir => true,
+        }
+    }
+}
+
 pub enum Input {
     /// Load source from file
     File(PathBuf),
@@ -526,6 +555,7 @@ pub fn basic_options() -> Options {
         incremental: None,
         debugging_opts: basic_debugging_options(),
         prints: Vec::new(),
+        borrowck_mode: BorrowckMode::Ast,
         cg: basic_codegen_options(),
         error_format: ErrorOutputType::default(),
         externs: Externs(BTreeMap::new()),
@@ -973,8 +1003,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "make unnamed regions display as '# (where # is some non-ident unique id)"),
     emit_end_regions: bool = (false, parse_bool, [UNTRACKED],
         "emit EndRegion as part of MIR; enable transforms that solely process EndRegion"),
-    borrowck_mir: bool = (false, parse_bool, [UNTRACKED],
-        "implicitly treat functions as if they have `#[rustc_mir_borrowck]` attribute"),
+    borrowck: Option<String> = (None, parse_opt_string, [UNTRACKED],
+        "select which borrowck is used (`ast`, `mir`, or `compare`)"),
     time_passes: bool = (false, parse_bool, [UNTRACKED],
         "measure time of each rustc pass"),
     count_llvm_insns: bool = (false, parse_bool,
@@ -1743,6 +1773,15 @@ pub fn build_session_options_and_crate_config(matches: &getopts::Matches)
         }
     }));
 
+    let borrowck_mode = match debugging_opts.borrowck.as_ref().map(|s| &s[..]) {
+        None | Some("ast") => BorrowckMode::Ast,
+        Some("mir") => BorrowckMode::Mir,
+        Some("compare") => BorrowckMode::Compare,
+        Some(m) => {
+            early_error(error_format, &format!("unknown borrowck mode `{}`", m))
+        },
+    };
+
     if !cg.remark.is_empty() && debuginfo == NoDebugInfo {
         early_warn(error_format, "-C remark will not show source locations without \
                                 --debuginfo");
@@ -1784,6 +1823,7 @@ pub fn build_session_options_and_crate_config(matches: &getopts::Matches)
         incremental,
         debugging_opts,
         prints,
+        borrowck_mode,
         cg,
         error_format,
         externs: Externs(externs),

src/librustc/session/mod.rs

@@ -416,7 +416,7 @@ impl Session {
     pub fn emit_end_regions(&self) -> bool {
         self.opts.debugging_opts.emit_end_regions ||
             (self.opts.debugging_opts.mir_emit_validate > 0) ||
-            self.opts.debugging_opts.borrowck_mir
+            self.opts.borrowck_mode.use_mir()
     }
     pub fn lto(&self) -> bool {
         self.opts.cg.lto || self.target.target.options.requires_lto

src/librustc_borrowck/borrowck/mod.rs

@@ -269,6 +269,17 @@ impl<'b, 'tcx: 'b> BorrowckErrors for BorrowckCtxt<'b, 'tcx> {
     {
         self.tcx.sess.struct_span_err(sp, msg)
     }
+
+    fn cancel_if_wrong_origin<'a>(&'a self,
+                                mut diag: DiagnosticBuilder<'a>,
+                                o: Origin)
+                                -> DiagnosticBuilder<'a>
+    {
+        if !o.should_emit_errors(self.tcx.sess.opts.borrowck_mode) {
+            self.tcx.sess.diagnostic().cancel(&mut diag);
+        }
+        diag
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////

src/librustc_mir/borrow_check.rs

@@ -54,7 +54,7 @@ fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 
     if {
         !tcx.has_attr(def_id, "rustc_mir_borrowck") &&
-            !tcx.sess.opts.debugging_opts.borrowck_mir &&
+            !tcx.sess.opts.borrowck_mode.use_mir() &&
             !tcx.sess.opts.debugging_opts.nll
     } {
         return;