syntax_pos: Introduce a helper for checking whether a span comes from expansion

src/librustc/lint/internal.rs

@@ -108,7 +108,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TyTyKind {
                             .help("try using `Ty` instead")
                             .emit();
                         } else {
-                            if ty.span.ctxt().outer_expn_info().is_some() {
+                            if ty.span.from_expansion() {
                                 return;
                             }
                             if let Some(t) = is_ty_or_ty_ctxt(cx, ty) {

src/librustc_codegen_ssa/mir/mod.rs

@@ -8,7 +8,7 @@ use crate::base;
 use crate::debuginfo::{self, VariableAccess, VariableKind, FunctionDebugContext};
 use crate::traits::*;
 
-use syntax_pos::{DUMMY_SP, NO_EXPANSION, BytePos, Span};
+use syntax_pos::{DUMMY_SP, BytePos, Span};
 use syntax::symbol::kw;
 
 use std::iter;
@@ -120,7 +120,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // In order to have a good line stepping behavior in debugger, we overwrite debug
         // locations of macro expansions with that of the outermost expansion site
         // (unless the crate is being compiled with `-Z debug-macros`).
-        if source_info.span.ctxt() == NO_EXPANSION ||
+        if !source_info.span.from_expansion() ||
            self.cx.sess().opts.debugging_opts.debug_macros {
             let scope = self.scope_metadata_for_loc(source_info.scope, source_info.span.lo());
             (scope, source_info.span)

src/librustc_lint/builtin.rs

@@ -42,7 +42,7 @@ use syntax::source_map::Spanned;
 use syntax::edition::Edition;
 use syntax::feature_gate::{self, AttributeGate, AttributeType};
 use syntax::feature_gate::{Stability, deprecated_attributes};
-use syntax_pos::{BytePos, Span, SyntaxContext};
+use syntax_pos::{BytePos, Span};
 use syntax::symbol::{Symbol, kw, sym};
 use syntax::errors::{Applicability, DiagnosticBuilder};
 use syntax::print::pprust::expr_to_string;
@@ -78,7 +78,7 @@ impl EarlyLintPass for WhileTrue {
         if let ast::ExprKind::While(cond, ..) = &e.node {
             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).node {
                 if let ast::LitKind::Bool(true) = lit.node {
-                    if lit.span.ctxt() == SyntaxContext::empty() {
+                    if !lit.span.from_expansion() {
                         let msg = "denote infinite loops with `loop { ... }`";
                         let condition_span = cx.sess.source_map().def_span(e.span);
                         cx.struct_span_lint(WHILE_TRUE, condition_span, msg)
@@ -167,7 +167,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonShorthandFieldPatterns {
                 if fieldpat.is_shorthand {
                     continue;
                 }
-                if fieldpat.span.ctxt().outer_expn_info().is_some() {
+                if fieldpat.span.from_expansion() {
                     // Don't lint if this is a macro expansion: macro authors
                     // shouldn't have to worry about this kind of style issue
                     // (Issue #49588)
@@ -1012,7 +1012,7 @@ impl UnreachablePub {
         let mut applicability = Applicability::MachineApplicable;
         match vis.node {
             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
-                if span.ctxt().outer_expn_info().is_some() {
+                if span.from_expansion() {
                     applicability = Applicability::MaybeIncorrect;
                 }
                 let def_span = cx.tcx.sess.source_map().def_span(span);

src/librustc_lint/unused.rs

@@ -518,7 +518,7 @@ impl EarlyLintPass for UnusedParens {
                 // when a parenthesized token tree matched in one macro expansion is matched as
                 // an expression in another and used as a fn/method argument (Issue #47775)
                 if e.span.ctxt().outer_expn_info()
-                    .map_or(false, |info| info.call_site.ctxt().outer_expn_info().is_some()) {
+                    .map_or(false, |info| info.call_site.from_expansion()) {
                         return;
                 }
                 let msg = format!("{} argument", call_kind);

src/librustc_resolve/lib.rs

@@ -274,7 +274,7 @@ impl<'tcx> Visitor<'tcx> for UsePlacementFinder {
                 ItemKind::Use(..) => {
                     // don't suggest placing a use before the prelude
                     // import or other generated ones
-                    if item.span.ctxt().outer_expn_info().is_none() {
+                    if !item.span.from_expansion() {
                         self.span = Some(item.span.shrink_to_lo());
                         self.found_use = true;
                         return;
@@ -284,7 +284,7 @@ impl<'tcx> Visitor<'tcx> for UsePlacementFinder {
                 ItemKind::ExternCrate(_) => {}
                 // but place them before the first other item
                 _ => if self.span.map_or(true, |span| item.span < span ) {
-                    if item.span.ctxt().outer_expn_info().is_none() {
+                    if !item.span.from_expansion() {
                         // don't insert between attributes and an item
                         if item.attrs.is_empty() {
                             self.span = Some(item.span.shrink_to_lo());

src/librustc_save_analysis/lib.rs

@@ -1156,7 +1156,7 @@ fn escape(s: String) -> String {
 // Helper function to determine if a span came from a
 // macro expansion or syntax extension.
 fn generated_code(span: Span) -> bool {
-    span.ctxt() != NO_EXPANSION || span.is_dummy()
+    span.from_expansion() || span.is_dummy()
 }
 
 // DefId::index is a newtype and so the JSON serialisation is ugly. Therefore

src/librustc_typeck/check/demand.rs

@@ -347,9 +347,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             sp,
         );
 
-        // Check the `expn_info()` to see if this is a macro; if so, it's hard to
-        // extract the text and make a good suggestion, so don't bother.
-        let is_macro = sp.ctxt().outer_expn_info().is_some();
+        // If the span is from a macro, then it's hard to extract the text
+        // and make a good suggestion, so don't bother.
+        let is_macro = sp.from_expansion();
 
         match (&expr.node, &expected.sty, &checked_ty.sty) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.sty, &check.sty) {

src/librustc_typeck/check/method/suggest.rs

@@ -985,7 +985,7 @@ impl hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
                 hir::ItemKind::Use(..) => {
                     // Don't suggest placing a `use` before the prelude
                     // import or other generated ones.
-                    if item.span.ctxt().outer_expn_info().is_none() {
+                    if !item.span.from_expansion() {
                         self.span = Some(item.span.shrink_to_lo());
                         self.found_use = true;
                         return;
@@ -995,7 +995,7 @@ impl hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
                 hir::ItemKind::ExternCrate(_) => {}
                 // ...but do place them before the first other item.
                 _ => if self.span.map_or(true, |span| item.span < span ) {
-                    if item.span.ctxt().outer_expn_info().is_none() {
+                    if !item.span.from_expansion() {
                         // Don't insert between attributes and an item.
                         if item.attrs.is_empty() {
                             self.span = Some(item.span.shrink_to_lo());

src/libsyntax/parse/parser.rs

@@ -1101,7 +1101,7 @@ impl<'a> Parser<'a> {
 
     crate fn process_potential_macro_variable(&mut self) {
         self.token = match self.token.kind {
-            token::Dollar if self.token.span.ctxt() != SyntaxContext::empty() &&
+            token::Dollar if self.token.span.from_expansion() &&
                              self.look_ahead(1, |t| t.is_ident()) => {
                 self.bump();
                 let name = match self.token.kind {

src/libsyntax_pos/hygiene.rs

@@ -255,7 +255,7 @@ impl HygieneData {
     }
 
     fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
-        while span.ctxt() != crate::NO_EXPANSION && span.ctxt() != to {
+        while span.from_expansion() && span.ctxt() != to {
             if let Some(info) = self.expn_info(self.outer_expn(span.ctxt())) {
                 span = info.call_site;
             } else {

src/libsyntax_pos/lib.rs

@@ -288,6 +288,12 @@ impl Span {
         span.lo.0 == 0 && span.hi.0 == 0
     }
 
+    /// Returns `true` if this span comes from a macro or desugaring.
+    #[inline]
+    pub fn from_expansion(self) -> bool {
+        self.ctxt() != SyntaxContext::empty()
+    }
+
     /// Returns a new span representing an empty span at the beginning of this span
     #[inline]
     pub fn shrink_to_lo(self) -> Span {

src/libsyntax_pos/symbol.rs

@@ -14,7 +14,6 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::str;
 
-use crate::hygiene::SyntaxContext;
 use crate::{Span, DUMMY_SP, GLOBALS};
 
 #[cfg(test)]
@@ -851,7 +850,7 @@ impl fmt::Display for Ident {
 
 impl Encodable for Ident {
     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
-        if self.span.ctxt().modern() == SyntaxContext::empty() {
+        if !self.span.modern().from_expansion() {
             s.emit_str(&self.as_str())
         } else { // FIXME(jseyfried): intercrate hygiene
             let mut string = "#".to_owned();