Auto merge of #43352 - estebank:macro-span-replacement, r=petrochenkov

Use the macro structure spans instead of the invocation

Fix #42104, CC #2887.

5 files changed, 52 insertions, 7 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index d2e51c9cb48..dc0848176d6 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1046,6 +1046,7 @@ impl<'feat> ExpansionConfig<'feat> {
 }
 
 // A Marker adds the given mark to the syntax context.
+#[derive(Debug)]
 pub struct Marker(pub Mark);
 
 impl Folder for Marker {
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index f786b1abb8a..8e746676ecd 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -119,8 +119,22 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
                     quoted::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
                     _ => cx.span_bug(sp, "malformed macro rhs"),
                 };
+
+                let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
                 // rhs has holes ( `$id` and `$(...)` that need filled)
-                let tts = transcribe(cx, Some(named_matches), rhs);
+                let mut tts = transcribe(cx, Some(named_matches), rhs);
+
+                // Replace all the tokens for the corresponding positions in the macro, to maintain
+                // proper positions in error reporting, while maintaining the macro_backtrace.
+                if rhs_spans.len() == tts.len() {
+                    tts = tts.map_enumerated(|i, tt| {
+                        let mut tt = tt.clone();
+                        let mut sp = rhs_spans[i];
+                        sp.ctxt = tt.span().ctxt;
+                        tt.set_span(sp);
+                        tt
+                    });
+                }
 
                 if cx.trace_macros() {
                     trace_macros_note(cx, sp, format!("to `{}`", tts));
diff --git a/src/libsyntax/ext/tt/quoted.rs b/src/libsyntax/ext/tt/quoted.rs
index 74fa85d130b..6fdcadd1dde 100644
--- a/src/libsyntax/ext/tt/quoted.rs
+++ b/src/libsyntax/ext/tt/quoted.rs
@@ -128,7 +128,7 @@ impl TokenTree {
         }
     }
 
-    /// Retrieve the TokenTree's span.
+    /// Retrieve the `TokenTree`'s span.
     pub fn span(&self) -> Span {
         match *self {
             TokenTree::Token(sp, _) |
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index ae3edfcbf32..553cac80d82 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -150,7 +150,7 @@ fn maybe_append(mut lhs: Vec<Attribute>, rhs: Option<Vec<Attribute>>)
     lhs
 }
 
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 enum PrevTokenKind {
     DocComment,
     Comma,
@@ -6090,8 +6090,7 @@ impl<'a> Parser<'a> {
             let (delim, tts) = self.expect_delimited_token_tree()?;
             if delim != token::Brace {
                 if !self.eat(&token::Semi) {
-                    let prev_span = self.prev_span;
-                    self.span_err(prev_span,
+                    self.span_err(self.prev_span,
                                   "macros that expand to items must either \
                                    be surrounded with braces or followed by \
                                    a semicolon");
@@ -6108,8 +6107,7 @@ impl<'a> Parser<'a> {
         match visibility {
             Visibility::Inherited => {}
             _ => {
-                let prev_span = self.prev_span;
-                return Err(self.span_fatal(prev_span, "unmatched visibility `pub`"));
+                return Err(self.span_fatal(self.prev_span, "unmatched visibility `pub`"));
             }
         }
 
diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs
index 8eee25405df..747bc7b4385 100644
--- a/src/libsyntax/tokenstream.rs
+++ b/src/libsyntax/tokenstream.rs
@@ -131,6 +131,15 @@ impl TokenTree {
         }
     }
 
+    /// Modify the `TokenTree`'s span inplace.
+    pub fn set_span(&mut self, span: Span) {
+        match *self {
+            TokenTree::Token(ref mut sp, _) | TokenTree::Delimited(ref mut sp, _) => {
+                *sp = span;
+            }
+        }
+    }
+
     /// Indicates if the stream is a token that is equal to the provided token.
     pub fn eq_token(&self, t: Token) -> bool {
         match *self {
@@ -190,6 +199,14 @@ impl PartialEq<TokenStream> for TokenStream {
 }
 
 impl TokenStream {
+    pub fn len(&self) -> usize {
+        if let TokenStreamKind::Stream(ref slice) = self.kind {
+            slice.len()
+        } else {
+            0
+        }
+    }
+
     pub fn empty() -> TokenStream {
         TokenStream { kind: TokenStreamKind::Empty }
     }
@@ -241,6 +258,21 @@ impl TokenStream {
         }
     }
 
+    pub fn map_enumerated<F: FnMut(usize, TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
+        let mut trees = self.into_trees();
+        let mut result = Vec::new();
+        let mut i = 0;
+        while let Some(stream) = trees.next_as_stream() {
+            result.push(match stream.kind {
+                TokenStreamKind::Tree(tree) => f(i, tree).into(),
+                TokenStreamKind::JointTree(tree) => f(i, tree).joint(),
+                _ => unreachable!()
+            });
+            i += 1;
+        }
+        TokenStream::concat(result)
+    }
+
     pub fn map<F: FnMut(TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
         let mut trees = self.into_trees();
         let mut result = Vec::new();