found the stack overflow culprit

hackeryarn · hackeryarn · commit ba90718bb44f · 2017-04-28T22:42:05.000-05:00
diff --git a/src/librustc/ty/maps.rs b/src/librustc/ty/maps.rs
@@ -346,8 +346,8 @@ macro_rules! define_maps {
                 }
 
                 // FIXME(eddyb) Get more valid Span's on queries.
-                if span == DUMMY_SP {
-                    span = key.default_span(tcx);
+                if span == DUMMY_SP && stringify!($name) != "def_span" {
+                    span = key.default_span(tcx)
                 }
 
                 let _task = tcx.dep_graph.in_task(Self::to_dep_node(&key));

Original file line number	Diff line number	Diff line change
`@@ -346,8 +346,8 @@ macro_rules! define_maps {`
`346`	`346`	`}`
`347`	`347`
`348`	`348`	`// FIXME(eddyb) Get more valid Span's on queries.`
`349`		`- if span == DUMMY_SP {`
`350`		`- span = key.default_span(tcx);`
	`349`	`+ if span == DUMMY_SP && stringify!($name) != "def_span" {`
	`350`	`+ span = key.default_span(tcx)`
`351`	`351`	`}`
`352`	`352`
`353`	`353`	`let _task = tcx.dep_graph.in_task(Self::to_dep_node(&key));`