Add a missing fmt::Debug impl lint

Closes rust-lang#20855

Author: sfackler

src/libcore/fmt/mod.rs

@@ -245,6 +245,7 @@ pub trait Show {
 #[unstable = "I/O and core have yet to be reconciled"]
 #[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is defined in your \
  crate, add `#[derive(Debug)]` or manually implement it"]
+#[lang = "debug_trait"]
 pub trait Debug {
  /// Formats the value using the given formatter.
  fn fmt(&self, &mut Formatter) -> Result;

src/librustc/lint/builtin.rs

@@ -1627,6 +1627,69 @@ impl LintPass for MissingCopyImplementations {
  }
 }
 
+declare_lint! {
+ MISSING_DEBUG_IMPLEMENTATIONS,
+ Allow,
+ "detects missing implementations of fmt::Debug"
+}
+
+pub struct MissingDebugImplementations {
+ impling_types: Option<NodeSet>,
+}
+
+impl MissingDebugImplementations {
+ pub fn new() -> MissingDebugImplementations {
+ MissingDebugImplementations {
+ impling_types: None,
+ }
+ }
+}
+
+impl LintPass for MissingDebugImplementations {
+ fn get_lints(&self) -> LintArray {
+ lint_array!(MISSING_DEBUG_IMPLEMENTATIONS)
+ }
+
+ fn check_item(&mut self, cx: &Context, item: &ast::Item) {
+ if !cx.exported_items.contains(&item.id) {
+ return;
+ }
+
+ match item.node {
+ ast::ItemStruct(..) | ast::ItemEnum(..) => {},
+ _ => return,
+ }
+
+ let debug = match cx.tcx.lang_items.debug_trait() {
+ Some(debug) => debug,
+ None => return,
+ };
+
+ if self.impling_types.is_none() {
+ let impls = cx.tcx.trait_impls.borrow();
+ let impls = match impls.get(&debug) {
+ Some(impls) => {
+ impls.borrow().iter()
+ .filter(|d| d.krate == ast::LOCAL_CRATE)
+ .filter_map(|d| ty::ty_to_def_id(ty::node_id_to_type(cx.tcx, d.node)))
+ .map(|d| d.node)
+ .collect()
+ }
+ None => NodeSet(),
+ };
+ self.impling_types = Some(impls);
+ debug!("{:?}", self.impling_types);
+ }
+
+ if !self.impling_types.as_ref().unwrap().contains(&item.id) {
+ cx.span_lint(MISSING_DEBUG_IMPLEMENTATIONS,
+ item.span,
+ "type does not implement `fmt::Debug`; consider adding #[derive(Debug)] \
+ or a manual implementation")
+ }
+ }
+}
+
 declare_lint! {
  DEPRECATED,
  Warn,

src/librustc/lint/context.rs

@@ -219,6 +219,7 @@ impl LintStore {
  RawPointerDerive,
  MissingDoc,
  Stability,
+ MissingDebugImplementations,
  );
 
  add_lint_group!(sess, "bad_style",

src/librustc/middle/lang_items.rs

@@ -328,4 +328,6 @@ lets_do_this! {
  IteratorItem, "iterator", iterator;
 
  StackExhaustedLangItem, "stack_exhausted", stack_exhausted;
+
+ DebugTraitLangItem, "debug_trait", debug_trait;
 }

src/test/compile-fail/missing_debug_impls.rs

@@ -0,0 +1,48 @@
+// Copyright 2015 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.
+
+// compile-flags: --crate-type lib
+#![deny(missing_debug_implementations)]
+#![allow(unused, unstable, missing_copy_implementations)]
+
+use std::fmt;
+
+pub enum A {} //~ ERROR type does not implement `fmt::Debug`
+
+#[derive(Debug)]
+pub enum B {}
+
+pub enum C {}
+
+impl fmt::Debug for C {
+ fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+ Ok(())
+ }
+}
+
+pub struct Foo; //~ ERROR type does not implement `fmt::Debug`
+
+#[derive(Debug)]
+pub struct Bar;
+
+pub struct Baz;
+
+impl fmt::Debug for Baz {
+ fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+ Ok(())
+ }
+}
+
+struct PrivateStruct;
+
+enum PrivateEnum {}
+
+#[derive(Debug)]
+struct GenericType<T>(T);