From 1bfa2483d587cbb41fb335e18459127394242ec1 Mon Sep 17 00:00:00 2001
From: Mazdak Farrokhzad <twingoow@gmail.com>
Date: Tue, 17 Mar 2020 12:54:57 +0100
Subject: [PATCH] defatalize `compile_declarative_macro`

---
 src/librustc_expand/mbe/macro_rules.rs        | 48 ++++++++++++-------
 ...ocal-ambiguity-multiple-parsing-options.rs |  8 ++++
 ...-ambiguity-multiple-parsing-options.stderr | 14 ++++++
 3 files changed, 54 insertions(+), 16 deletions(-)
 create mode 100644 src/test/ui/macros/local-ambiguity-multiple-parsing-options.rs
 create mode 100644 src/test/ui/macros/local-ambiguity-multiple-parsing-options.stderr

diff --git a/src/librustc_expand/mbe/macro_rules.rs b/src/librustc_expand/mbe/macro_rules.rs
index d4fe382b84b..6377347585c 100644
--- a/src/librustc_expand/mbe/macro_rules.rs
+++ b/src/librustc_expand/mbe/macro_rules.rs
@@ -15,7 +15,7 @@ use rustc_ast_pretty::pprust;
 use rustc_attr::{self as attr, TransparencyError};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Applicability, DiagnosticBuilder, FatalError};
+use rustc_errors::{Applicability, DiagnosticBuilder};
 use rustc_feature::Features;
 use rustc_parse::parser::Parser;
 use rustc_session::parse::ParseSess;
@@ -180,6 +180,19 @@ impl TTMacroExpander for MacroRulesMacroExpander {
     }
 }
 
+struct MacroRulesDummyExpander;
+
+impl TTMacroExpander for MacroRulesDummyExpander {
+    fn expand<'cx>(
+        &self,
+        _: &'cx mut ExtCtxt<'_>,
+        sp: Span,
+        _: TokenStream,
+    ) -> Box<dyn MacResult + 'cx> {
+        DummyResult::any(sp)
+    }
+}
+
 fn trace_macros_note(cx_expansions: &mut FxHashMap<Span, Vec<String>>, sp: Span, message: String) {
     let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
     cx_expansions.entry(sp).or_default().push(message);
@@ -362,6 +375,18 @@ pub fn compile_declarative_macro(
     def: &ast::Item,
     edition: Edition,
 ) -> SyntaxExtension {
+    let mk_syn_ext = |expander| {
+        SyntaxExtension::new(
+            sess,
+            SyntaxExtensionKind::LegacyBang(expander),
+            def.span,
+            Vec::new(),
+            edition,
+            def.ident.name,
+            &def.attrs,
+        )
+    };
+
     let diag = &sess.span_diagnostic;
     let lhs_nm = ast::Ident::new(sym::lhs, def.span);
     let rhs_nm = ast::Ident::new(sym::rhs, def.span);
@@ -416,13 +441,12 @@ pub fn compile_declarative_macro(
         Failure(token, msg) => {
             let s = parse_failure_msg(&token);
             let sp = token.span.substitute_dummy(def.span);
-            let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
-            err.span_label(sp, msg);
-            err.emit();
-            FatalError.raise();
+            sess.span_diagnostic.struct_span_err(sp, &s).span_label(sp, msg).emit();
+            return mk_syn_ext(Box::new(MacroRulesDummyExpander));
         }
-        Error(sp, s) => {
-            sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
+        Error(sp, msg) => {
+            sess.span_diagnostic.struct_span_err(sp.substitute_dummy(def.span), &msg).emit();
+            return mk_syn_ext(Box::new(MacroRulesDummyExpander));
         }
     };
 
@@ -494,15 +518,7 @@ pub fn compile_declarative_macro(
         valid,
     });
 
-    SyntaxExtension::new(
-        sess,
-        SyntaxExtensionKind::LegacyBang(expander),
-        def.span,
-        Vec::new(),
-        edition,
-        def.ident.name,
-        &def.attrs,
-    )
+    mk_syn_ext(expander)
 }
 
 fn check_lhs_nt_follows(
diff --git a/src/test/ui/macros/local-ambiguity-multiple-parsing-options.rs b/src/test/ui/macros/local-ambiguity-multiple-parsing-options.rs
new file mode 100644
index 00000000000..3967481098c
--- /dev/null
+++ b/src/test/ui/macros/local-ambiguity-multiple-parsing-options.rs
@@ -0,0 +1,8 @@
+fn main() {}
+
+macro_rules! ambiguity {
+    ($($i:ident)* $j:ident) => {};
+}
+
+ambiguity!(error); //~ ERROR local ambiguity
+ambiguity!(error); //~ ERROR local ambiguity
diff --git a/src/test/ui/macros/local-ambiguity-multiple-parsing-options.stderr b/src/test/ui/macros/local-ambiguity-multiple-parsing-options.stderr
new file mode 100644
index 00000000000..0ae56c42221
--- /dev/null
+++ b/src/test/ui/macros/local-ambiguity-multiple-parsing-options.stderr
@@ -0,0 +1,14 @@
+error: local ambiguity: multiple parsing options: built-in NTs ident ('i') or ident ('j').
+  --> $DIR/local-ambiguity-multiple-parsing-options.rs:7:12
+   |
+LL | ambiguity!(error);
+   |            ^^^^^
+
+error: local ambiguity: multiple parsing options: built-in NTs ident ('i') or ident ('j').
+  --> $DIR/local-ambiguity-multiple-parsing-options.rs:8:12
+   |
+LL | ambiguity!(error);
+   |            ^^^^^
+
+error: aborting due to 2 previous errors
+