Add suggestion to lint

src/librustc/lint/builtin.rs

@@ -332,7 +332,8 @@ impl LintPass for HardwiredLints {
 #[derive(PartialEq, RustcEncodable, RustcDecodable, Debug)]
 pub enum BuiltinLintDiagnostics {
     Normal,
-    BareTraitObject(Span, /* is_global */ bool)
+    BareTraitObject(Span, /* is_global */ bool),
+    AbsPathWithModule(Span),
 }
 
 impl BuiltinLintDiagnostics {
@@ -347,6 +348,23 @@ impl BuiltinLintDiagnostics {
                 };
                 db.span_suggestion(span, "use `dyn`", sugg);
             }
+            BuiltinLintDiagnostics::AbsPathWithModule(span) => {
+                let sugg = match sess.codemap().span_to_snippet(span) {
+                    Ok(ref s) => {
+                        // FIXME(Manishearth) ideally the emitting code
+                        // can tell us whether or not this is global
+                        let opt_colon = if s.trim_left().starts_with("::") {
+                            ""
+                        } else {
+                            "::"
+                        };
+
+                        format!("crate{}{}", opt_colon, s)
+                    }
+                    Err(_) => format!("crate::<path>")
+                };
+                db.span_suggestion(span, "use `crate`", sugg);
+            }
         }
     }
 }

src/librustc_resolve/lib.rs

@@ -3344,11 +3344,14 @@ impl<'a> Resolver<'a> {
                                 }
 
                                 if !is_crate {
-                                    self.session.buffer_lint(
+                                    let diag = lint::builtin::BuiltinLintDiagnostics
+                                                   ::AbsPathWithModule(path_span);
+                                    self.session.buffer_lint_with_diagnostic(
                                         lint::builtin::ABSOLUTE_PATH_STARTING_WITH_MODULE,
                                         id, path_span,
-                                        "Fully-qualified paths must start with `self`, `super`,
-                                        `crate`, or an external crate name in the 2018 edition");
+                                        "Absolute paths must start with `self`, `super`, \
+                                        `crate`, or an external crate name in the 2018 edition",
+                                        diag);
                                 }
                             }
                         }