Include scope names in diagnostics

So far, rustc has only printed about filenames and line numbers for
warnings and errors. I think it is rather missed, compared to `gcc`
and other compiler, that useful context information such as function
names and structs is not included.

The changes in this pull request introduce a new line emission in
diagnostics to implement this.

Author: da-x

src/librustc_driver/driver.rs

@@ -196,6 +196,11 @@ pub fn compile_input(
             )?
         };
 
+        // Let diagnostics access the AST for allowing to show function names in messages.
+        let expanded_crate = Lrc::new(expanded_crate);
+        sess.diagnostic().set_ast(
+            Box::new(syntax::diagnostics::ast::ContextResolver::new(expanded_crate.clone())));
+
         let output_paths = generated_output_paths(sess, &outputs, output.is_some(), &crate_name);
 
         // Ensure the source file isn't accidentally overwritten during compilation.
@@ -257,7 +262,7 @@ pub fn compile_input(
                     &hir_map,
                     &analysis,
                     &resolutions,
-                    &expanded_crate,
+                    &*expanded_crate,
                     &hir_map.krate(),
                     &outputs,
                     &crate_name
@@ -267,8 +272,10 @@ pub fn compile_input(
         }
 
         let opt_crate = if control.keep_ast {
-            Some(&expanded_crate)
+            Some(&*expanded_crate)
         } else {
+            // AST will be kept for scope naming in diagnostic, should
+            // depricate keep_ast?
             drop(expanded_crate);
             None
         };

src/librustc_errors/emitter.rs

@@ -26,6 +26,10 @@ use std::cmp::min;
 use termcolor::{StandardStream, ColorChoice, ColorSpec, BufferWriter};
 use termcolor::{WriteColor, Color, Buffer};
 use unicode_width;
+use SpanContextResolver;
+use SpanContextKind;
+use SpanContext;
+use std::cell::RefCell;
 
 const ANONYMIZED_LINE_NUM: &str = "LL";
 
@@ -81,6 +85,7 @@ impl Emitter for EmitterWriter {
         self.emit_messages_default(&db.level,
                                    &db.styled_message(),
                                    &db.code,
+                                   &db.handler.context_resolver,
                                    &primary_span,
                                    &children,
                                    &suggestions);
@@ -958,6 +963,7 @@ impl EmitterWriter {
                             msp: &MultiSpan,
                             msg: &Vec<(String, Style)>,
                             code: &Option<DiagnosticId>,
+                            cr: &RefCell<Option<Box<SpanContextResolver>>>,
                             level: &Level,
                             max_line_num_len: usize,
                             is_secondary: bool)
@@ -1042,6 +1048,18 @@ impl EmitterWriter {
                                            cm.doctest_offset_line(loc.line),
                                            loc.col.0 + 1),
                                   Style::LineAndColumn);
+                    if let Some(ref primary_span) = msp.primary_span().as_ref() {
+                        if primary_span != &&DUMMY_SP {
+                            if let &Some(ref rc) = &*cr.borrow() {
+                                let context = rc.span_to_context(**primary_span);
+                                if let Some(context) = context {
+                                    repr_styled_context(buffer_msg_line_offset,
+                                                        &mut buffer, context);
+                                }
+                            }
+                        }
+                    }
+
                     for _ in 0..max_line_num_len {
                         buffer.prepend(buffer_msg_line_offset, " ", Style::NoStyle);
                     }
@@ -1282,6 +1300,7 @@ impl EmitterWriter {
                              level: &Level,
                              message: &Vec<(String, Style)>,
                              code: &Option<DiagnosticId>,
+                             cr: &RefCell<Option<Box<SpanContextResolver>>>,
                              span: &MultiSpan,
                              children: &Vec<SubDiagnostic>,
                              suggestions: &[CodeSuggestion]) {
@@ -1294,6 +1313,7 @@ impl EmitterWriter {
         match self.emit_message_default(span,
                                         message,
                                         code,
+                                        cr,
                                         level,
                                         max_line_num_len,
                                         false) {
@@ -1315,6 +1335,7 @@ impl EmitterWriter {
                         match self.emit_message_default(&span,
                                                         &child.styled_message(),
                                                         &None,
+                                                        cr,
                                                         &child.level,
                                                         max_line_num_len,
                                                         true) {
@@ -1396,6 +1417,23 @@ fn overlaps(a1: &Annotation, a2: &Annotation, padding: usize) -> bool {
     num_overlap(a1.start_col, a1.end_col + padding, a2.start_col, a2.end_col, false)
 }
 
+fn repr_styled_context(line_offset: usize, buffer: &mut StyledBuffer, context: SpanContext)
+{
+    let kind_str = match context.kind {
+        SpanContextKind::Enum => "enum",
+        SpanContextKind::Module => "mod",
+        SpanContextKind::Function => "fn",
+        SpanContextKind::Impl => "impl",
+        SpanContextKind::Method => "fn",
+        SpanContextKind::Struct => "struct",
+        SpanContextKind::Trait => "trait",
+        SpanContextKind::Union => "union",
+    };
+
+    buffer.append(line_offset, &format!(": in {}", kind_str), Style::NoStyle);
+    buffer.append(line_offset, &format!(" {}", context.path), Style::HeaderMsg);
+}
+
 fn emit_to_destination(rendered_buffer: &Vec<Vec<StyledString>>,
                        lvl: &Level,
                        dst: &mut Destination,

src/librustc_errors/lib.rs

@@ -38,7 +38,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::stable_hasher::StableHasher;
 
 use std::borrow::Cow;
-use std::cell::Cell;
+use std::cell::{Cell, RefCell};
 use std::{error, fmt};
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering::SeqCst;
@@ -286,6 +286,9 @@ pub struct Handler {
     // this handler. These hashes is used to avoid emitting the same error
     // twice.
     emitted_diagnostics: Lock<FxHashSet<u128>>,
+
+    // Callback to the Span AST resolver
+    context_resolver: RefCell<Option<Box<SpanContextResolver>>>,
 }
 
 fn default_track_diagnostic(_: &Diagnostic) {}
@@ -300,6 +303,32 @@ pub struct HandlerFlags {
     pub external_macro_backtrace: bool,
 }
 
+pub enum SpanContextKind {
+    Enum,
+    Function,
+    Impl,
+    Method,
+    Struct,
+    Trait,
+    Union,
+    Module,
+}
+
+pub struct SpanContext {
+    kind: SpanContextKind,
+    path: String,
+}
+
+impl SpanContext {
+    pub fn new(kind: SpanContextKind, path: String) -> Self {
+        Self { kind, path }
+    }
+}
+
+pub trait SpanContextResolver {
+    fn span_to_context(&self, sp: Span) -> Option<SpanContext>;
+}
+
 impl Handler {
     pub fn with_tty_emitter(color_config: ColorConfig,
                             can_emit_warnings: bool,
@@ -347,9 +376,14 @@ impl Handler {
             taught_diagnostics: Lock::new(FxHashSet()),
             emitted_diagnostic_codes: Lock::new(FxHashSet()),
             emitted_diagnostics: Lock::new(FxHashSet()),
+            context_resolver: RefCell::new(None),
         }
     }
 
+    pub fn set_ast(&self, scr: Box<SpanContextResolver>) {
+        *self.context_resolver.borrow_mut() = Some(scr);
+    }
+
     pub fn set_continue_after_error(&self, continue_after_error: bool) {
         self.continue_after_error.set(continue_after_error);
     }

src/libsyntax/diagnostics/ast.rs

@@ -0,0 +1,109 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use ast::*;
+use errors::{SpanContextResolver, SpanContextKind, SpanContext};
+use rustc_data_structures::sync::Lrc;
+use syntax_pos::Span;
+use visit::{self, Visitor, FnKind};
+
+pub struct ContextResolver {
+    krate: Lrc<Crate>
+}
+
+impl ContextResolver {
+    pub fn new(krate: Lrc<Crate>) -> Self {
+        Self { krate }
+    }
+}
+
+struct SpanResolver {
+    idents: Vec<Ident>,
+    kind: Option<SpanContextKind>,
+    span: Span,
+}
+
+impl<'ast> Visitor<'ast> for SpanResolver {
+    fn visit_trait_item(&mut self, ti: &'ast TraitItem) {
+        if ti.span.proper_contains(self.span) {
+            self.idents.push(ti.ident);
+            self.kind = Some(SpanContextKind::Trait);
+            visit::walk_trait_item(self, ti)
+        }
+    }
+
+    fn visit_impl_item(&mut self, ii: &'ast ImplItem) {
+        if ii.span.proper_contains(self.span) {
+            self.idents.push(ii.ident);
+            self.kind = Some(SpanContextKind::Impl);
+            visit::walk_impl_item(self, ii)
+        }
+    }
+
+    fn visit_item(&mut self, i: &'ast Item) {
+        if i.span.proper_contains(self.span) {
+            let kind = match i.node {
+                ItemKind::Enum(..) => Some(SpanContextKind::Enum),
+                ItemKind::Struct(..) => Some(SpanContextKind::Struct),
+                ItemKind::Union(..) => Some(SpanContextKind::Union),
+                ItemKind::Trait(..) => Some(SpanContextKind::Trait),
+                ItemKind::Mod(..) => Some(SpanContextKind::Module),
+                _ => None,
+            };
+
+            if kind.is_some() {
+                self.idents.push(i.ident);
+                self.kind = kind;
+            }
+
+            visit::walk_item(self, i);
+        }
+    }
+
+    fn visit_fn(&mut self, fk: FnKind<'ast>, fd: &'ast FnDecl, s: Span, _: NodeId) {
+        if s.proper_contains(self.span) {
+            match fk {
+                FnKind::ItemFn(ref ident, ..) => {
+                    self.idents.push(*ident);
+                    self.kind = Some(SpanContextKind::Function);
+                }
+                FnKind::Method(ref ident, ..) => {
+                    self.idents.push(*ident);
+                    self.kind = Some(SpanContextKind::Method);
+                }
+                _ => {}
+            }
+
+            visit::walk_fn(self, fk, fd, s)
+        }
+    }
+}
+
+impl SpanContextResolver for ContextResolver {
+    fn span_to_context(&self, sp: Span) -> Option<SpanContext> {
+        let mut sr = SpanResolver {
+            idents: Vec::new(),
+            span: sp,
+            kind: None,
+        };
+        visit::walk_crate(&mut sr, &*self.krate);
+
+        let SpanResolver { kind, idents, .. } = sr;
+
+        match kind {
+            None => None,
+            Some(kind) => {
+                let path = idents.iter().map(
+                    |x| x.to_string()).collect::<Vec<String>>().join("::");
+                Some(SpanContext::new(kind, path))
+            }
+        }
+    }
+}

src/libsyntax/lib.rs

@@ -106,6 +106,7 @@ pub mod diagnostics {
     pub mod macros;
     pub mod plugin;
     pub mod metadata;
+    pub mod ast;
 }
 
 // NB: This module needs to be declared first so diagnostics are

src/libsyntax_pos/lib.rs

@@ -265,6 +265,12 @@ impl Span {
         span.lo <= other.lo && other.hi <= span.hi
     }
 
+    pub fn proper_contains(self, other: Span) -> bool {
+        let span = self.data();
+        let other = other.data();
+        span.lo < other.lo && other.hi < span.hi
+    }
+
     /// Return true if the spans are equal with regards to the source text.
     ///
     /// Use this instead of `==` when either span could be generated code,