use snippet for making a suggestion if possible

Author: rhysd

Diff for: clippy_lints/src/dbg_macro.rs

@@ -1,7 +1,10 @@
-use crate::utils::span_help_and_lint;
+use crate::utils::{span_help_and_lint, span_lint_and_sugg, snippet_opt};
 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
 use rustc::{declare_tool_lint, lint_array};
 use syntax::ast;
+use rustc_errors::Applicability;
+use syntax::tokenstream::TokenStream;
+use syntax::source_map::Span;
 
 /// **What it does:** Checks for usage of dbg!() macro.
 ///
@@ -40,13 +43,39 @@ impl LintPass for Pass {
 impl EarlyLintPass for Pass {
     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
         if mac.node.path == "dbg" {
-            span_help_and_lint(
-                cx,
-                DBG_MACRO,
-                mac.span,
-                "`dbg!` macro is intended as a debugging tool",
-                "ensure to avoid having uses of it in version control",
-            );
+            match tts_span(mac.node.tts.clone()).and_then(|span| snippet_opt(cx, span)) {
+                Some(sugg) => {
+                    span_lint_and_sugg(
+                        cx,
+                        DBG_MACRO,
+                        mac.span,
+                        "`dbg!` macro is intended as a debugging tool",
+                        "ensure to avoid having uses of it in version control",
+                        sugg,
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+                None => {
+                    span_help_and_lint(
+                        cx,
+                        DBG_MACRO,
+                        mac.span,
+                        "`dbg!` macro is intended as a debugging tool",
+                        "ensure to avoid having uses of it in version control",
+                    );
+                }
+            };
         }
     }
 }
+
+// Get span enclosing entire the token stream.
+fn tts_span(tts: TokenStream) -> Option<Span> {
+    let mut cursor = tts.into_trees();
+    let first = cursor.next()?.span();
+    let span = match cursor.last() {
+        Some(tree) => first.to(tree.span()),
+        None => first,
+    };
+    Some(span)
+}

Diff for: tests/ui/dbg_macro.stderr

@@ -5,55 +5,70 @@ LL |     if let Some(n) = dbg!(n.checked_sub(4)) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::dbg-macro` implied by `-D warnings`
-   = help: ensure to avoid having uses of it in version control
+help: ensure to avoid having uses of it in version control
+   |
+LL |     if let Some(n) = n.checked_sub(4) {
+   |                      ^^^^^^^^^^^^^^^^
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:12:8
    |
 LL |     if dbg!(n <= 1) {
    |        ^^^^^^^^^^^^
+help: ensure to avoid having uses of it in version control
    |
-   = help: ensure to avoid having uses of it in version control
+LL |     if n <= 1 {
+   |        ^^^^^^
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:13:9
    |
 LL |         dbg!(1)
    |         ^^^^^^^
+help: ensure to avoid having uses of it in version control
+   |
+LL |         1
    |
-   = help: ensure to avoid having uses of it in version control
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:15:9
    |
 LL |         dbg!(n * factorial(n - 1))
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: ensure to avoid having uses of it in version control
+   |
+LL |         n * factorial(n - 1)
    |
-   = help: ensure to avoid having uses of it in version control
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:20:5
    |
 LL |     dbg!(42);
    |     ^^^^^^^^
+help: ensure to avoid having uses of it in version control
    |
-   = help: ensure to avoid having uses of it in version control
+LL |     42;
+   |     ^^
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:21:5
    |
 LL |     dbg!(dbg!(dbg!(42)));
    |     ^^^^^^^^^^^^^^^^^^^^
+help: ensure to avoid having uses of it in version control
    |
-   = help: ensure to avoid having uses of it in version control
+LL |     dbg!(dbg!(42));
+   |     ^^^^^^^^^^^^^^
 
 error: `dbg!` macro is intended as a debugging tool
   --> $DIR/dbg_macro.rs:22:14
    |
 LL |     foo(3) + dbg!(factorial(4));
    |              ^^^^^^^^^^^^^^^^^^
+help: ensure to avoid having uses of it in version control
    |
-   = help: ensure to avoid having uses of it in version control
+LL |     foo(3) + factorial(4);
+   |              ^^^^^^^^^^^^
 
 error: aborting due to 7 previous errors