Rollup merge of #55298 - estebank:macro-def, r=pnkfelix

Point at macro definition when no rules expect token

Fix #35150.

3 files changed, 39 insertions, 13 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 5bf1a7dd663..1701c8da2c5 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -247,8 +247,13 @@ impl<F> AttrProcMacro for F
 
 /// Represents a thing that maps token trees to Macro Results
 pub trait TTMacroExpander {
-    fn expand<'cx>(&self, ecx: &'cx mut ExtCtxt, span: Span, input: TokenStream)
-                   -> Box<dyn MacResult+'cx>;
+    fn expand<'cx>(
+        &self,
+        ecx: &'cx mut ExtCtxt,
+        span: Span,
+        input: TokenStream,
+        def_span: Option<Span>,
+    ) -> Box<dyn MacResult+'cx>;
 }
 
 pub type MacroExpanderFn =
@@ -259,8 +264,13 @@ impl<F> TTMacroExpander for F
     where F: for<'cx> Fn(&'cx mut ExtCtxt, Span, &[tokenstream::TokenTree])
     -> Box<dyn MacResult+'cx>
 {
-    fn expand<'cx>(&self, ecx: &'cx mut ExtCtxt, span: Span, input: TokenStream)
-                   -> Box<dyn MacResult+'cx> {
+    fn expand<'cx>(
+        &self,
+        ecx: &'cx mut ExtCtxt,
+        span: Span,
+        input: TokenStream,
+        _def_span: Option<Span>,
+    ) -> Box<dyn MacResult+'cx> {
         struct AvoidInterpolatedIdents;
 
         impl Folder for AvoidInterpolatedIdents {
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 4deeb4a43d9..33b651e1b38 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -764,7 +764,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                                                     edition) {
                     dummy_span
                 } else {
-                    kind.make_from(expander.expand(self.cx, span, mac.node.stream()))
+                    kind.make_from(expander.expand(self.cx, span, mac.node.stream(), None))
                 }
             }
 
@@ -785,7 +785,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                                                     edition) {
                     dummy_span
                 } else {
-                    kind.make_from(expander.expand(self.cx, span, mac.node.stream()))
+                    kind.make_from(expander.expand(
+                        self.cx,
+                        span,
+                        mac.node.stream(),
+                        def_info.map(|(_, s)| s),
+                    ))
                 }
             }
 
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 5e53b8b99c7..543dc478d7b 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -79,16 +79,19 @@ struct MacroRulesMacroExpander {
 }
 
 impl TTMacroExpander for MacroRulesMacroExpander {
-    fn expand<'cx>(&self,
-                   cx: &'cx mut ExtCtxt,
-                   sp: Span,
-                   input: TokenStream)
-                   -> Box<dyn MacResult+'cx> {
+    fn expand<'cx>(
+        &self,
+        cx: &'cx mut ExtCtxt,
+        sp: Span,
+        input: TokenStream,
+        def_span: Option<Span>,
+    ) -> Box<dyn MacResult+'cx> {
         if !self.valid {
             return DummyResult::any(sp);
         }
         generic_extension(cx,
                           sp,
+                          def_span,
                           self.name,
                           input,
                           &self.lhses,
@@ -104,6 +107,7 @@ fn trace_macros_note(cx: &mut ExtCtxt, sp: Span, message: String) {
 /// Given `lhses` and `rhses`, this is the new macro we create
 fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
                           sp: Span,
+                          def_span: Option<Span>,
                           name: ast::Ident,
                           arg: TokenStream,
                           lhses: &[quoted::TokenTree],
@@ -183,7 +187,14 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
     }
 
     let best_fail_msg = parse_failure_msg(best_fail_tok.expect("ran no matchers"));
-    let mut err = cx.struct_span_err(best_fail_spot.substitute_dummy(sp), &best_fail_msg);
+    let span = best_fail_spot.substitute_dummy(sp);
+    let mut err = cx.struct_span_err(span, &best_fail_msg);
+    err.span_label(span, best_fail_msg);
+    if let Some(sp) = def_span {
+        if cx.source_map().span_to_filename(sp).is_real() && !sp.is_dummy() {
+            err.span_label(cx.source_map().def_span(sp), "when calling this macro");
+        }
+    }
 
     // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
     if let Some((arg, comma_span)) = arg.add_comma() {
@@ -194,7 +205,7 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
             };
             match TokenTree::parse(cx, lhs_tt, arg.clone()) {
                 Success(_) => {
-                    if comma_span == DUMMY_SP {
+                    if comma_span.is_dummy() {
                         err.note("you might be missing a comma");
                     } else {
                         err.span_suggestion_short_with_applicability(