From b47e3d8fe4dc6c22157e9d458a3f619a3860b8f8 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Sat, 28 Sep 2019 12:04:06 -0700
Subject: [PATCH 1/8] Stabilize --extern flag without a path.

---
 src/doc/rustc/src/command-line-arguments.md               | 7 ++++++-
 src/librustc/session/config.rs                            | 7 -------
 src/librustdoc/config.rs                                  | 4 ----
 src/test/run-make-fulldeps/extern-flag-fun/Makefile       | 1 -
 src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile | 3 +--
 5 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/src/doc/rustc/src/command-line-arguments.md b/src/doc/rustc/src/command-line-arguments.md
index 79b4f7542f9b0..5887a0869e68c 100644
--- a/src/doc/rustc/src/command-line-arguments.md
+++ b/src/doc/rustc/src/command-line-arguments.md
@@ -264,7 +264,12 @@ This flag, when combined with other flags, makes them produce extra output.
 
 This flag allows you to pass the name and location of an external crate that
 will be linked into the crate you are building. This flag may be specified
-multiple times. The format of the value should be `CRATENAME=PATH`.
+multiple times. This flag takes an argument with either of the following
+formats:
+
+* `CRATENAME=PATH` — Indicates the given crate is found at the given path.
+* `CRATENAME` — Indicates the given crate may be found in the search path,
+  such as within the sysroot or via the `-L` flag.
 
 <a id="option-sysroot"></a>
 ## `--sysroot`: Override the system root
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 2bcddeaf1962d..1740d8fe96751 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -2392,13 +2392,6 @@ fn parse_externs(
         let name = parts.next().unwrap_or_else(||
             early_error(error_format, "--extern value must not be empty"));
         let location = parts.next().map(|s| s.to_string());
-        if location.is_none() && !is_unstable_enabled {
-            early_error(
-                error_format,
-                "the `-Z unstable-options` flag must also be passed to \
-                 enable `--extern crate_name` without `=path`",
-            );
-        };
 
         let entry = externs
             .entry(name.to_owned())
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 0b8d4d6c302f1..255d5f9f35dbf 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -615,10 +615,6 @@ fn parse_externs(matches: &getopts::Matches) -> Result<Externs, String> {
         let mut parts = arg.splitn(2, '=');
         let name = parts.next().ok_or("--extern value must not be empty".to_string())?;
         let location = parts.next().map(|s| s.to_string());
-        if location.is_none() && !nightly_options::is_unstable_enabled(matches) {
-            return Err("the `-Z unstable-options` flag must also be passed to \
-                        enable `--extern crate_name` without `=path`".to_string());
-        }
         let name = name.to_string();
         // For Rustdoc purposes, we can treat all externs as public
         externs.entry(name)
diff --git a/src/test/run-make-fulldeps/extern-flag-fun/Makefile b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
index a9f2585335003..7f54d6ea3bc6c 100644
--- a/src/test/run-make-fulldeps/extern-flag-fun/Makefile
+++ b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
@@ -4,7 +4,6 @@ all:
 	$(RUSTC) bar.rs --crate-type=rlib
 	$(RUSTC) bar.rs --crate-type=rlib -C extra-filename=-a
 	$(RUSTC) bar-alt.rs --crate-type=rlib
-	$(RUSTC) foo.rs --extern hello && exit 1 || exit 0
 	$(RUSTC) foo.rs --extern bar=no-exist && exit 1 || exit 0
 	$(RUSTC) foo.rs --extern bar=foo.rs && exit 1 || exit 0
 	$(RUSTC) foo.rs \
diff --git a/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile b/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
index bf98fcd10cfde..36288c4b870e7 100644
--- a/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
+++ b/src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile
@@ -1,8 +1,7 @@
 -include ../tools.mk
 
 all: extern_absolute_paths.rs krate2
-	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018 \
-		-Z unstable-options --extern krate2
+	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018 --extern krate2
 	cat $(TMPDIR)/save-analysis/extern_absolute_paths.json | "$(PYTHON)" validate_json.py
 
 krate2: krate2.rs

From e0058ce99408124f689177e895d753341a5fc9ee Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Sun, 29 Sep 2019 18:17:27 -0700
Subject: [PATCH 2/8] Add more --extern tests.

---
 .../extern-flag-pathless/Makefile              | 18 ++++++++++++++++++
 .../extern-flag-pathless/bar-dynamic.rs        |  3 +++
 .../extern-flag-pathless/bar-static.rs         |  3 +++
 .../extern-flag-pathless/foo.rs                |  3 +++
 src/test/rustdoc/inline_cross/use_crate.rs     |  2 +-
 .../ui-fulldeps/pathless-extern-unstable.rs    | 10 ++++++++++
 .../pathless-extern-unstable.stderr            | 12 ++++++++++++
 src/test/ui/pathless-extern-ok.rs              |  9 +++++++++
 8 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 src/test/run-make-fulldeps/extern-flag-pathless/Makefile
 create mode 100644 src/test/run-make-fulldeps/extern-flag-pathless/bar-dynamic.rs
 create mode 100644 src/test/run-make-fulldeps/extern-flag-pathless/bar-static.rs
 create mode 100644 src/test/run-make-fulldeps/extern-flag-pathless/foo.rs
 create mode 100644 src/test/ui-fulldeps/pathless-extern-unstable.rs
 create mode 100644 src/test/ui-fulldeps/pathless-extern-unstable.stderr
 create mode 100644 src/test/ui/pathless-extern-ok.rs

diff --git a/src/test/run-make-fulldeps/extern-flag-pathless/Makefile b/src/test/run-make-fulldeps/extern-flag-pathless/Makefile
new file mode 100644
index 0000000000000..4849fc62f4a95
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-pathless/Makefile
@@ -0,0 +1,18 @@
+-include ../tools.mk
+
+# Test mixing pathless --extern with paths.
+
+all:
+	$(RUSTC) bar-static.rs --crate-name=bar --crate-type=rlib
+	$(RUSTC) bar-dynamic.rs --crate-name=bar --crate-type=dylib -C prefer-dynamic
+	# rlib preferred over dylib
+	$(RUSTC) foo.rs --extern bar
+	$(call RUN,foo) | $(CGREP) 'static'
+	$(RUSTC) foo.rs --extern bar=$(TMPDIR)/libbar.rlib --extern bar
+	$(call RUN,foo) | $(CGREP) 'static'
+	# explicit --extern overrides pathless
+	$(RUSTC) foo.rs --extern bar=$(call DYLIB,bar) --extern bar
+	$(call RUN,foo) | $(CGREP) 'dynamic'
+	# prefer-dynamic does what it says
+	$(RUSTC) foo.rs --extern bar -C prefer-dynamic
+	$(call RUN,foo) | $(CGREP) 'dynamic'
diff --git a/src/test/run-make-fulldeps/extern-flag-pathless/bar-dynamic.rs b/src/test/run-make-fulldeps/extern-flag-pathless/bar-dynamic.rs
new file mode 100644
index 0000000000000..e2d68d517ff97
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-pathless/bar-dynamic.rs
@@ -0,0 +1,3 @@
+pub fn f() {
+    println!("dynamic");
+}
diff --git a/src/test/run-make-fulldeps/extern-flag-pathless/bar-static.rs b/src/test/run-make-fulldeps/extern-flag-pathless/bar-static.rs
new file mode 100644
index 0000000000000..240d8bde4d186
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-pathless/bar-static.rs
@@ -0,0 +1,3 @@
+pub fn f() {
+    println!("static");
+}
diff --git a/src/test/run-make-fulldeps/extern-flag-pathless/foo.rs b/src/test/run-make-fulldeps/extern-flag-pathless/foo.rs
new file mode 100644
index 0000000000000..1ea64da7dad26
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-pathless/foo.rs
@@ -0,0 +1,3 @@
+fn main() {
+    bar::f();
+}
diff --git a/src/test/rustdoc/inline_cross/use_crate.rs b/src/test/rustdoc/inline_cross/use_crate.rs
index f678ba0a46c0d..00e0f041c56fe 100644
--- a/src/test/rustdoc/inline_cross/use_crate.rs
+++ b/src/test/rustdoc/inline_cross/use_crate.rs
@@ -2,7 +2,7 @@
 // aux-build:use_crate_2.rs
 // build-aux-docs
 // edition:2018
-// compile-flags:--extern use_crate --extern use_crate_2 -Z unstable-options
+// compile-flags:--extern use_crate --extern use_crate_2
 
 // During the buildup to Rust 2018, rustdoc would eagerly inline `pub use some_crate;` as if it
 // were a module, so we changed it to make `pub use`ing crate roots remain as a `pub use` statement
diff --git a/src/test/ui-fulldeps/pathless-extern-unstable.rs b/src/test/ui-fulldeps/pathless-extern-unstable.rs
new file mode 100644
index 0000000000000..a5a31816c9572
--- /dev/null
+++ b/src/test/ui-fulldeps/pathless-extern-unstable.rs
@@ -0,0 +1,10 @@
+// ignore-stage1
+// edition:2018
+// compile-flags:--extern rustc
+
+// Test that `--extern rustc` fails with `rustc_private`.
+
+pub use rustc;
+//~^ use of unstable library feature 'rustc_private'
+
+fn main() {}
diff --git a/src/test/ui-fulldeps/pathless-extern-unstable.stderr b/src/test/ui-fulldeps/pathless-extern-unstable.stderr
new file mode 100644
index 0000000000000..edc3b1c58be22
--- /dev/null
+++ b/src/test/ui-fulldeps/pathless-extern-unstable.stderr
@@ -0,0 +1,12 @@
+error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+  --> $DIR/pathless-extern-unstable.rs:7:9
+   |
+LL | pub use rustc;
+   |         ^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/27812
+   = help: add `#![feature(rustc_private)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/pathless-extern-ok.rs b/src/test/ui/pathless-extern-ok.rs
new file mode 100644
index 0000000000000..0ffa5eb894040
--- /dev/null
+++ b/src/test/ui/pathless-extern-ok.rs
@@ -0,0 +1,9 @@
+// edition:2018
+// compile-flags:--extern alloc
+// build-pass
+
+// Test that `--extern alloc` will load from the sysroot without error.
+
+fn main() {
+    let _: Vec<i32> = alloc::vec::Vec::new();
+}

From 4bf411ea6d8e348accfa66b86e18395af2038fe9 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Sun, 29 Sep 2019 18:17:48 -0700
Subject: [PATCH 3/8] Update built-in help for --extern.

---
 src/librustc/session/config.rs | 2 +-
 src/librustdoc/lib.rs          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 1740d8fe96751..b1284280f8791 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1800,7 +1800,7 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
             "",
             "extern",
             "Specify where an external rust library is located",
-            "NAME=PATH",
+            "NAME[=PATH]",
         ),
         opt::multi_s(
             "",
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 8cd32a3d1b508..13b8809e23e40 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -140,7 +140,7 @@ fn opts() -> Vec<RustcOptGroup> {
         }),
         stable("cfg", |o| o.optmulti("", "cfg", "pass a --cfg to rustc", "")),
         stable("extern", |o| {
-            o.optmulti("", "extern", "pass an --extern to rustc", "NAME=PATH")
+            o.optmulti("", "extern", "pass an --extern to rustc", "NAME[=PATH]")
         }),
         unstable("extern-html-root-url", |o| {
             o.optmulti("", "extern-html-root-url",

From b54e8ecc2e0eec9ab9d0b1c1d9cb55f7602800c4 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Sun, 29 Sep 2019 18:20:03 -0700
Subject: [PATCH 4/8] Update extern linking documentation.

---
 src/doc/rustc/src/codegen-options/index.md  |  6 ++++-
 src/doc/rustc/src/command-line-arguments.md | 28 ++++++++++++++++-----
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/src/doc/rustc/src/codegen-options/index.md b/src/doc/rustc/src/codegen-options/index.md
index 70c7acccd3638..0dc81378e05b2 100644
--- a/src/doc/rustc/src/codegen-options/index.md
+++ b/src/doc/rustc/src/codegen-options/index.md
@@ -197,7 +197,11 @@ in software.
 ## prefer-dynamic
 
 By default, `rustc` prefers to statically link dependencies. This option will
-make it use dynamic linking instead.
+indicate that dynamic linking should be used if possible if both a static and
+dynamic versions of a library are available. There is an internal algorithm
+for determining whether or not it is possible to statically or dynamically
+link with a dependency. For example, `cdylib` crate types may only use static
+linkage.
 
 ## no-integrated-as
 
diff --git a/src/doc/rustc/src/command-line-arguments.md b/src/doc/rustc/src/command-line-arguments.md
index 5887a0869e68c..561856db54b0d 100644
--- a/src/doc/rustc/src/command-line-arguments.md
+++ b/src/doc/rustc/src/command-line-arguments.md
@@ -21,8 +21,7 @@ to `#[cfg(verbose)]` and `#[cfg(feature = "serde")]` respectively.
 <a id="option-l-search-path"></a>
 ## `-L`: add a directory to the library search path
 
-When looking for external crates or libraries, a directory passed to this flag
-will be searched.
+The `-L` flag adds a path to search for external crates and libraries.
 
 The kind of search path can optionally be specified with the form `-L
 KIND=PATH` where `KIND` may be one of:
@@ -262,15 +261,32 @@ This flag, when combined with other flags, makes them produce extra output.
 <a id="option-extern"></a>
 ## `--extern`: specify where an external library is located
 
-This flag allows you to pass the name and location of an external crate that
-will be linked into the crate you are building. This flag may be specified
-multiple times. This flag takes an argument with either of the following
-formats:
+This flag allows you to pass the name and location for an external crate of a
+direct dependency. Indirect dependencies (dependencies of dependencies) are
+located using the [`-L` flag](#option-l-search-path). The given crate name is
+added to the [extern prelude], which is the same as specifying `extern crate`
+within the root module. The given crate name does not need to match the name
+the library was built with.
+
+This flag may be specified multiple times. This flag takes an argument with
+either of the following formats:
 
 * `CRATENAME=PATH` — Indicates the given crate is found at the given path.
 * `CRATENAME` — Indicates the given crate may be found in the search path,
   such as within the sysroot or via the `-L` flag.
 
+The same crate name may be specified multiple times for different crate types.
+For loading metadata, `rlib` takes precedence over `rmeta`, which takes
+precedence over `dylib`. If both an `rlib` and `dylib` are found, an internal
+algorithm is used to decide which to use for linking. The [`-C prefer-dynamic`
+flag][prefer-dynamic] may be used to influence which is used.
+
+If the same crate name is specified with and without a path, the one with the
+path is used and the pathless flag has no effect.
+
+[extern prelude]: ../reference/items/extern-crates.html#extern-prelude
+[prefer-dynamic]: codegen-options/index.md#prefer-dynamic
+
 <a id="option-sysroot"></a>
 ## `--sysroot`: Override the system root
 

From 41e051dfcceb18ae6a50ca02800444545360873a Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Mon, 7 Oct 2019 07:58:28 -0700
Subject: [PATCH 5/8] Update src/test/ui-fulldeps/pathless-extern-unstable.rs

Add ERROR

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>
---
 src/test/ui-fulldeps/pathless-extern-unstable.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/test/ui-fulldeps/pathless-extern-unstable.rs b/src/test/ui-fulldeps/pathless-extern-unstable.rs
index a5a31816c9572..00b3ec5409ff0 100644
--- a/src/test/ui-fulldeps/pathless-extern-unstable.rs
+++ b/src/test/ui-fulldeps/pathless-extern-unstable.rs
@@ -5,6 +5,6 @@
 // Test that `--extern rustc` fails with `rustc_private`.
 
 pub use rustc;
-//~^ use of unstable library feature 'rustc_private'
+//~^ ERROR use of unstable library feature 'rustc_private'
 
 fn main() {}

From f9e4f0f4946c81efb847238012a403d079a596ee Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Tue, 8 Oct 2019 09:45:24 -0700
Subject: [PATCH 6/8] Add test for --extern alloc=librustc.rlib

---
 src/test/run-make-fulldeps/extern-flag-fun/Makefile          | 3 +++
 src/test/run-make-fulldeps/extern-flag-fun/gated_unstable.rs | 3 +++
 src/test/run-make-fulldeps/extern-flag-fun/rustc.rs          | 1 +
 3 files changed, 7 insertions(+)
 create mode 100644 src/test/run-make-fulldeps/extern-flag-fun/gated_unstable.rs
 create mode 100644 src/test/run-make-fulldeps/extern-flag-fun/rustc.rs

diff --git a/src/test/run-make-fulldeps/extern-flag-fun/Makefile b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
index 7f54d6ea3bc6c..38d1d5bb8488a 100644
--- a/src/test/run-make-fulldeps/extern-flag-fun/Makefile
+++ b/src/test/run-make-fulldeps/extern-flag-fun/Makefile
@@ -14,3 +14,6 @@ all:
 		--extern bar=$(TMPDIR)/libbar.rlib \
 		--extern bar=$(TMPDIR)/libbar-a.rlib
 	$(RUSTC) foo.rs --extern bar=$(TMPDIR)/libbar.rlib
+	# Try to be sneaky and load a private crate from with a non-private name.
+	$(RUSTC) rustc.rs -Zforce-unstable-if-unmarked --crate-type=rlib
+	$(RUSTC) gated_unstable.rs --extern alloc=$(TMPDIR)/librustc.rlib 2>&1 | $(CGREP) 'rustc_private'
diff --git a/src/test/run-make-fulldeps/extern-flag-fun/gated_unstable.rs b/src/test/run-make-fulldeps/extern-flag-fun/gated_unstable.rs
new file mode 100644
index 0000000000000..03600c830fff6
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-fun/gated_unstable.rs
@@ -0,0 +1,3 @@
+extern crate alloc;
+
+fn main() {}
diff --git a/src/test/run-make-fulldeps/extern-flag-fun/rustc.rs b/src/test/run-make-fulldeps/extern-flag-fun/rustc.rs
new file mode 100644
index 0000000000000..b76b4321d62aa
--- /dev/null
+++ b/src/test/run-make-fulldeps/extern-flag-fun/rustc.rs
@@ -0,0 +1 @@
+pub fn foo() {}

From 845ec5df7af7fa9cc0d4c52ff61b38160e9dcc37 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Wed, 16 Oct 2019 07:37:53 -0700
Subject: [PATCH 7/8] Remove docs on --extern metadata precedence.

---
 src/doc/rustc/src/command-line-arguments.md | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/doc/rustc/src/command-line-arguments.md b/src/doc/rustc/src/command-line-arguments.md
index 561856db54b0d..577d03d1038f8 100644
--- a/src/doc/rustc/src/command-line-arguments.md
+++ b/src/doc/rustc/src/command-line-arguments.md
@@ -276,9 +276,8 @@ either of the following formats:
   such as within the sysroot or via the `-L` flag.
 
 The same crate name may be specified multiple times for different crate types.
-For loading metadata, `rlib` takes precedence over `rmeta`, which takes
-precedence over `dylib`. If both an `rlib` and `dylib` are found, an internal
-algorithm is used to decide which to use for linking. The [`-C prefer-dynamic`
+If both an `rlib` and `dylib` are found, an internal algorithm is used to
+decide which to use for linking. The [`-C prefer-dynamic`
 flag][prefer-dynamic] may be used to influence which is used.
 
 If the same crate name is specified with and without a path, the one with the

From ee459c6200c6384ac83ffd7f33de12f123134c30 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Wed, 16 Oct 2019 09:55:40 -0700
Subject: [PATCH 8/8] Update for unstable option refactoring.

---
 src/librustc/session/config.rs | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index b1284280f8791..eb5654e80a82c 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -2164,7 +2164,6 @@ fn collect_print_requests(
     cg: &mut CodegenOptions,
     dopts: &mut DebuggingOptions,
     matches: &getopts::Matches,
-    is_unstable_enabled: bool,
     error_format: ErrorOutputType,
 ) -> Vec<PrintRequest> {
     let mut prints = Vec::<PrintRequest>::new();
@@ -2206,7 +2205,7 @@ fn collect_print_requests(
         "tls-models" => PrintRequest::TlsModels,
         "native-static-libs" => PrintRequest::NativeStaticLibs,
         "target-spec-json" => {
-            if is_unstable_enabled {
+            if dopts.unstable_options {
                 PrintRequest::TargetSpec
             } else {
                 early_error(
@@ -2370,7 +2369,6 @@ fn parse_externs(
     matches: &getopts::Matches,
     debugging_opts: &DebuggingOptions,
     error_format: ErrorOutputType,
-    is_unstable_enabled: bool,
 ) -> Externs {
     if matches.opt_present("extern-private") && !debugging_opts.unstable_options {
         early_error(
@@ -2476,12 +2474,10 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         );
     }
 
-    let is_unstable_enabled = nightly_options::is_unstable_enabled(matches);
     let prints = collect_print_requests(
         &mut cg,
         &mut debugging_opts,
         matches,
-        is_unstable_enabled,
         error_format,
     );
 
@@ -2514,7 +2510,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         );
     }
 
-    let externs = parse_externs(matches, &debugging_opts, error_format, is_unstable_enabled);
+    let externs = parse_externs(matches, &debugging_opts, error_format);
 
     let crate_name = matches.opt_str("crate-name");