Auto merge of #41907 - est31:macro_unused, r=jseyfried

Add lint for unused macros

Addresses parts of #34938, to add a lint for unused macros.

We now output warnings by default when we encounter a macro that we didn't use for expansion.

Issues to be resolved before this PR is ready for merge:

- [x] fix the NodeId issue described above
- [x] remove all unused macros from rustc and the libraries or set `#[allow(unused_macros)]` next to them if they should be kept for some reason. This is needed for successful boostrap and bors to accept the PR. -> #41934
- [x] ~~implement the full extent of #34938, that means the macro match arm checking as well.~~ *let's not do this for now*

3 files changed, 11 insertions, 3 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index f731c5abdd6..86202f77dbf 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -535,7 +535,7 @@ pub enum SyntaxExtension {
     ///
     /// The `bool` dictates whether the contents of the macro can
     /// directly use `#[unstable]` things (true == yes).
-    NormalTT(Box<TTMacroExpander>, Option<Span>, bool),
+    NormalTT(Box<TTMacroExpander>, Option<(ast::NodeId, Span)>, bool),
 
     /// A function-like syntax extension that has an extra ident before
     /// the block.
@@ -589,6 +589,7 @@ pub trait Resolver {
                      -> Result<Option<Rc<SyntaxExtension>>, Determinacy>;
     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy>;
+    fn check_unused_macros(&self);
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -618,6 +619,7 @@ impl Resolver for DummyResolver {
                      _force: bool) -> Result<Rc<SyntaxExtension>, Determinacy> {
         Err(Determinacy::Determined)
     }
+    fn check_unused_macros(&self) {}
 }
 
 #[derive(Clone)]
@@ -800,6 +802,10 @@ impl<'a> ExtCtxt<'a> {
     pub fn name_of(&self, st: &str) -> ast::Name {
         Symbol::intern(st)
     }
+
+    pub fn check_unused_macros(&self) {
+        self.resolver.check_unused_macros();
+    }
 }
 
 /// Extract a string literal from the macro expanded version of `expr`,
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index a8aa103f80a..75dd09f2311 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -469,7 +469,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     call_site: span,
                     callee: NameAndSpan {
                         format: MacroBang(Symbol::intern(&format!("{}", path))),
-                        span: exp_span,
+                        span: exp_span.map(|(_, s)| s),
                         allow_internal_unstable: allow_internal_unstable,
                     },
                 });
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index f959ccc989e..39a60e5c080 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -252,7 +252,9 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
         valid: valid,
     });
 
-    NormalTT(exp, Some(def.span), attr::contains_name(&def.attrs, "allow_internal_unstable"))
+    NormalTT(exp,
+             Some((def.id, def.span)),
+             attr::contains_name(&def.attrs, "allow_internal_unstable"))
 }
 
 fn check_lhs_nt_follows(sess: &ParseSess,