1 files changed, 38 insertions, 32 deletions

diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index 162da2ac54c..44df8a6d3da 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -243,6 +243,10 @@ pub struct NameAndSpan {
     pub name: String,
     /// The format with which the macro was invoked.
     pub format: MacroFormat,
+    /// Whether the macro is allowed to use #[unstable]/feature-gated
+    /// features internally without forcing the whole crate to opt-in
+    /// to them.
+    pub allow_internal_unstable: bool,
     /// The span of the macro definition itself. The macro may not
     /// have a sensible definition span (e.g. something defined
     /// completely inside libsyntax) in which case this is None.
@@ -830,41 +834,43 @@ impl CodeMap {
         }
     }
 
-    /// Check if a span is "internal" to a macro. This means that it is entirely generated by a
-    /// macro expansion and contains no code that was passed in as an argument.
-    pub fn span_is_internal(&self, span: Span) -> bool {
-        // first, check if the given expression was generated by a macro or not
-        // we need to go back the expn_info tree to check only the arguments
-        // of the initial macro call, not the nested ones.
-        let mut is_internal = false;
-        let mut expnid = span.expn_id;
-        while self.with_expn_info(expnid, |expninfo| {
-            match expninfo {
-                Some(ref info) => {
-                    // save the parent expn_id for next loop iteration
-                    expnid = info.call_site.expn_id;
-                    if info.callee.name == "format_args" {
-                        // This is a hack because the format_args builtin calls unstable APIs.
-                        // I spent like 6 hours trying to solve this more generally but am stupid.
-                        is_internal = true;
-                        false
-                    } else if info.callee.span.is_none() {
-                        // it's a compiler built-in, we *really* don't want to mess with it
-                        // so we skip it, unless it was called by a regular macro, in which case
-                        // we will handle the caller macro next turn
-                        is_internal = true;
-                        true // continue looping
+    /// Check if a span is "internal" to a macro in which #[unstable]
+    /// items can be used (that is, a macro marked with
+    /// `#[allow_internal_unstable]`).
+    pub fn span_allows_unstable(&self, span: Span) -> bool {
+        debug!("span_allows_unstable(span = {:?})", span);
+        let mut allows_unstable = false;
+        let mut expn_id = span.expn_id;
+        loop {
+            let quit = self.with_expn_info(expn_id, |expninfo| {
+                debug!("span_allows_unstable: expninfo = {:?}", expninfo);
+                expninfo.map_or(/* hit the top level */ true, |info| {
+
+                    let span_comes_from_this_expansion =
+                        info.callee.span.map_or(span == info.call_site, |mac_span| {
+                            mac_span.lo <= span.lo && span.hi < mac_span.hi
+                        });
+
+                    debug!("span_allows_unstable: from this expansion? {}, allows unstable? {}",
+                           span_comes_from_this_expansion,
+                           info.callee.allow_internal_unstable);
+                    if span_comes_from_this_expansion {
+                        allows_unstable = info.callee.allow_internal_unstable;
+                        // we've found the right place, stop looking
+                        true
                     } else {
-                        // was this expression from the current macro arguments ?
-                        is_internal = !( span.lo > info.call_site.lo &&
-                                         span.hi < info.call_site.hi );
-                        true // continue looping
+                        // not the right place, keep looking
+                        expn_id = info.call_site.expn_id;
+                        false
                     }
-                },
-                _ => false // stop looping
+                })
+            });
+            if quit {
+                break
             }
-        }) { /* empty while loop body */ }
-        return is_internal;
+        }
+        debug!("span_allows_unstable? {}", allows_unstable);
+        allows_unstable
     }
 }