implement dbg_macro rule (fixes rust-lang#3721)

Author: rhysd

clippy_lints/src/dbg_macro.rs

@@ -0,0 +1,51 @@
+use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
+use rustc::{declare_tool_lint, lint_array};
+use crate::utils::span_lint;
+use syntax::ast;
+
+/// **What it does:** Checks for usage of dbg!() macro not to have it in
+/// version control.
+///
+/// **Why is this bad?** `dbg!` macro is intended as a debugging tool.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust,ignore
+/// // Bad
+/// dbg!(true)
+///
+/// // Good
+/// true
+/// ```
+declare_clippy_lint! {
+    pub DBG_MACRO,
+    style,
+    "`dbg!` macro is intended as a debugging tool"
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct Pass;
+
+impl LintPass for Pass {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(DBG_MACRO)
+    }
+
+    fn name(&self) -> &'static str {
+        "DbgMacro"
+    }
+}
+
+impl EarlyLintPass for Pass {
+    fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
+        if mac.node.path == "dbg" {
+            span_lint(
+                cx,
+                DBG_MACRO,
+                mac.span,
+                "`dbg!` macro is intended as a debugging tool. ensure to avoid having uses of it in version control",
+            );
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -94,6 +94,7 @@ pub mod const_static_lifetime;
 pub mod copies;
 pub mod copy_iterator;
 pub mod cyclomatic_complexity;
+pub mod dbg_macro;
 pub mod default_trait_access;
 pub mod derive;
 pub mod doc;
@@ -231,6 +232,7 @@ pub fn register_pre_expansion_lints(
         },
     );
     store.register_pre_expansion_pass(Some(session), true, false, box attrs::CfgAttrPass);
+    store.register_pre_expansion_pass(Some(session), true, false, box dbg_macro::Pass);
 }
 
 pub fn read_conf(reg: &rustc_plugin::Registry<'_>) -> Conf {
@@ -589,6 +591,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         copies::IFS_SAME_COND,
         copies::IF_SAME_THEN_ELSE,
         cyclomatic_complexity::CYCLOMATIC_COMPLEXITY,
+        dbg_macro::DBG_MACRO,
         derive::DERIVE_HASH_XOR_EQ,
         double_comparison::DOUBLE_COMPARISONS,
         double_parens::DOUBLE_PARENS,
@@ -800,6 +803,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         block_in_if_condition::BLOCK_IN_IF_CONDITION_STMT,
         collapsible_if::COLLAPSIBLE_IF,
         const_static_lifetime::CONST_STATIC_LIFETIME,
+        dbg_macro::DBG_MACRO,
         enum_variants::ENUM_VARIANT_NAMES,
         enum_variants::MODULE_INCEPTION,
         eq_op::OP_REF,

tests/ui/dbg_macro.rs

@@ -0,0 +1,3 @@
+fn main() {
+    dbg!(42);
+}

tests/ui/dbg_macro.stderr

@@ -0,0 +1,10 @@
+error: `dbg!` macro is intended as a debugging tool. ensure to avoid having uses of it in version control
+  --> $DIR/dbg_macro.rs:2:5
+   |
+LL |     dbg!(42);
+   |     ^^^^^^^^
+   |
+   = note: `-D clippy::dbg-macro` implied by `-D warnings`
+
+error: aborting due to previous error
+