Extend ParseSess to support buffering lints

src/librustc/lint/builtin.rs

@@ -331,6 +331,15 @@
      via the module system"
 }
 
+/// Some lints that are buffered from `libsyntax`. See `syntax::early_buffered_lints`.
+pub mod parser {
+    declare_lint! {
+        pub QUESTION_MARK_MACRO_SEP,
+        Warn,
+        "detects the use of `?` as a macro separator"
+    }
+}
+
 /// Does nothing as a lint pass, but registers some `Lint`s
 /// which are used by other parts of the compiler.
 #[derive(Copy, Clone)]
@@ -389,6 +398,7 @@ fn get_lints(&self) -> LintArray {
             WHERE_CLAUSES_OBJECT_SAFETY,
             PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
             MACRO_USE_EXTERN_CRATE,
+            parser::QUESTION_MARK_MACRO_SEP,
         )
     }
 }

src/librustc/lint/mod.rs

@@ -38,10 +38,12 @@
 use hir::intravisit;
 use hir;
 use lint::builtin::BuiltinLintDiagnostics;
+use lint::builtin::parser::QUESTION_MARK_MACRO_SEP;
 use session::{Session, DiagnosticMessageId};
 use std::{hash, ptr};
 use syntax::ast;
 use syntax::codemap::{MultiSpan, ExpnFormat};
+use syntax::early_buffered_lints::BufferedEarlyLintId;
 use syntax::edition::Edition;
 use syntax::symbol::Symbol;
 use syntax::visit as ast_visit;
@@ -86,6 +88,13 @@ pub struct Lint {
 }
 
 impl Lint {
+    /// Returns the `rust::lint::Lint` for a `syntax::early_buffered_lints::BufferedEarlyLintId`.
+    pub fn from_parser_lint_id(lint_id: BufferedEarlyLintId) -> &'static Self {
+        match lint_id {
+            BufferedEarlyLintId::QuestionMarkMacroSep => QUESTION_MARK_MACRO_SEP,
+        }
+    }
+
     /// Get the lint's name, with ASCII letters converted to lowercase.
     pub fn name_lower(&self) -> String {
         self.name.to_ascii_lowercase()

src/librustc_driver/driver.rs

@@ -52,6 +52,7 @@
 use rustc_data_structures::sync::{self, Lrc, Lock};
 use std::sync::mpsc;
 use syntax::{self, ast, attr, diagnostics, visit};
+use syntax::early_buffered_lints::BufferedEarlyLint;
 use syntax::ext::base::ExtCtxt;
 use syntax::fold::Folder;
 use syntax::parse::{self, PResult};
@@ -696,6 +697,13 @@ pub fn phase_1_parse_input<'a>(
         hir_stats::print_ast_stats(&krate, "PRE EXPANSION AST STATS");
     }
 
+    // Add all buffered lints from the `ParseSess` to the `Session`.
+    let mut parse_sess_buffered = sess.parse_sess.buffered_lints.borrow_mut();
+    for BufferedEarlyLint{id, span, msg, lint_id} in parse_sess_buffered.drain(..) {
+        let lint = lint::Lint::from_parser_lint_id(lint_id);
+        sess.buffer_lint(lint, id, span, &msg);
+    }
+
     Ok(krate)
 }
 

src/libsyntax/early_buffered_lints.rs

@@ -0,0 +1,29 @@
+//! Allows the buffering of lints for later.
+//!
+//! Since we cannot have a dependency on `librustc`, we implement some types here that are somewhat
+//! redundant. Later, these types can be converted to types for use by the rest of the compiler.
+
+use syntax::ast::NodeId;
+use syntax_pos::MultiSpan;
+
+/// Since we cannot import `LintId`s from `rustc::lint`, we define some Ids here which can later be
+/// passed to `rustc::lint::Lint::from_parser_lint_id` to get a `rustc::lint::Lint`.
+pub enum BufferedEarlyLintId {
+    /// Usage of `?` as a macro separator is deprecated.
+    QuestionMarkMacroSep,
+}
+
+/// Stores buffered lint info which can later be passed to `librustc`.
+pub struct BufferedEarlyLint {
+    /// The span of code that we are linting on.
+   pub span: MultiSpan,
+
+   /// The lint message.
+   pub msg: String,
+
+   /// The `NodeId` of the AST node that generated the lint.
+   pub id: NodeId,
+
+   /// A lint Id that can be passed to `rustc::lint::Lint::from_parser_lint_id`.
+   pub lint_id: BufferedEarlyLintId,
+}

src/libsyntax/lib.rs

@@ -181,6 +181,8 @@ pub mod tt {
     }
 }
 
+pub mod early_buffered_lints;
+
 #[cfg(test)]
 mod test_snippet;
 

src/libsyntax/parse/mod.rs

@@ -11,9 +11,10 @@
 //! The main parser interface
 
 use rustc_data_structures::sync::{Lrc, Lock};
-use ast::{self, CrateConfig};
+use ast::{self, CrateConfig, NodeId};
+use early_buffered_lints::{BufferedEarlyLint, BufferedEarlyLintId};
 use codemap::{CodeMap, FilePathMapping};
-use syntax_pos::{Span, FileMap, FileName};
+use syntax_pos::{Span, FileMap, FileName, MultiSpan};
 use errors::{Handler, ColorConfig, DiagnosticBuilder};
 use feature_gate::UnstableFeatures;
 use parse::parser::Parser;
@@ -57,6 +58,7 @@ pub struct ParseSess {
     /// Used to determine and report recursive mod inclusions
     included_mod_stack: Lock<Vec<PathBuf>>,
     code_map: Lrc<CodeMap>,
+    pub buffered_lints: Lock<Vec<BufferedEarlyLint>>,
 }
 
 impl ParseSess {
@@ -80,12 +82,29 @@ pub fn with_span_handler(handler: Handler, code_map: Lrc<CodeMap>) -> ParseSess
             included_mod_stack: Lock::new(vec![]),
             code_map,
             non_modrs_mods: Lock::new(vec![]),
+            buffered_lints: Lock::new(vec![]),
         }
     }
 
     pub fn codemap(&self) -> &CodeMap {
         &self.code_map
     }
+
+    pub fn buffer_lint<S: Into<MultiSpan>>(&self,
+        lint_id: BufferedEarlyLintId,
+        span: S,
+        id: NodeId,
+        msg: &str,
+    ) {
+        self.buffered_lints
+            .borrow_mut()
+            .push(BufferedEarlyLint{
+                span: span.into(),
+                id,
+                msg: msg.into(),
+                lint_id,
+            });
+    }
 }
 
 #[derive(Clone)]