From a678e3191197f145451c97c6cc884e15cae38186 Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Sat, 14 Sep 2019 16:17:57 -0400
Subject: [PATCH] Hide diagnostics emitted during --cfg parsing

The early error is more than sufficient for fixing the problem.
---
 src/librustc/session/config.rs                      | 13 ++++++++++++-
 .../ui/conditional-compilation/cfg-arg-invalid-6.rs |  3 +++
 .../cfg-arg-invalid-6.stderr                        |  2 ++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/conditional-compilation/cfg-arg-invalid-6.rs
 create mode 100644 src/test/ui/conditional-compilation/cfg-arg-invalid-6.stderr

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index c74b2fee41d6c..723855c7c29cf 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -7,6 +7,7 @@ use crate::session::{early_error, early_warn, Session};
 use crate::session::search_paths::SearchPath;
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::sync::Lrc;
 
 use rustc_target::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, RelroLevel};
 use rustc_target::spec::{Target, TargetTriple};
@@ -19,6 +20,7 @@ use syntax::parse::{ParseSess, new_parser_from_source_str};
 use syntax::parse::token;
 use syntax::symbol::{sym, Symbol};
 use syntax::feature_gate::UnstableFeatures;
+use syntax::source_map::SourceMap;
 
 use errors::emitter::HumanReadableErrorType;
 use errors::{ColorConfig, FatalError, Handler};
@@ -1850,11 +1852,20 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
     opts
 }
 
+struct NullEmitter;
+
+impl errors::emitter::Emitter for NullEmitter {
+    fn emit_diagnostic(&mut self, _: &errors::DiagnosticBuilder<'_>) {}
+}
+
 // Converts strings provided as `--cfg [cfgspec]` into a `crate_cfg`.
 pub fn parse_cfgspecs(cfgspecs: Vec<String>) -> FxHashSet<(String, Option<String>)> {
     syntax::with_default_globals(move || {
         let cfg = cfgspecs.into_iter().map(|s| {
-            let sess = ParseSess::new(FilePathMapping::empty());
+
+            let cm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+            let handler = Handler::with_emitter(false, None, Box::new(NullEmitter));
+            let sess = ParseSess::with_span_handler(handler, cm);
             let filename = FileName::cfg_spec_source_code(&s);
             let mut parser = new_parser_from_source_str(&sess, filename, s.to_string());
 
diff --git a/src/test/ui/conditional-compilation/cfg-arg-invalid-6.rs b/src/test/ui/conditional-compilation/cfg-arg-invalid-6.rs
new file mode 100644
index 0000000000000..9fa726f93e3ea
--- /dev/null
+++ b/src/test/ui/conditional-compilation/cfg-arg-invalid-6.rs
@@ -0,0 +1,3 @@
+// compile-flags: --cfg a{
+// error-pattern: invalid `--cfg` argument: `a{` (expected `key` or `key="value"`)
+fn main() {}
diff --git a/src/test/ui/conditional-compilation/cfg-arg-invalid-6.stderr b/src/test/ui/conditional-compilation/cfg-arg-invalid-6.stderr
new file mode 100644
index 0000000000000..7d2087b4b71f7
--- /dev/null
+++ b/src/test/ui/conditional-compilation/cfg-arg-invalid-6.stderr
@@ -0,0 +1,2 @@
+error: invalid `--cfg` argument: `a{` (expected `key` or `key="value"`)
+