From 2bcc15188854ff184c85426b5aa60535ed1bd8a8 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Tue, 11 Aug 2015 20:53:50 +0200
Subject: [PATCH] new lint for Option.unwrap() and Result.unwrap()

The latter is set to Allow by default (fixes #24)
---
 src/lib.rs                    |  4 ++++
 src/methods.rs                | 39 +++++++++++++++++++++++++++++++++++
 tests/compile-fail/methods.rs | 11 ++++++++++
 3 files changed, 54 insertions(+)
 create mode 100644 src/methods.rs
 create mode 100755 tests/compile-fail/methods.rs

diff --git a/src/lib.rs b/src/lib.rs
index 80ba04031fa..4009aa1cf8d 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,6 +29,7 @@ pub mod collapsible_if;
 pub mod unicode;
 pub mod utils;
 pub mod strings;
+pub mod methods;
 
 #[plugin_registrar]
 pub fn plugin_registrar(reg: &mut Registry) {
@@ -55,6 +56,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_lint_pass(box unicode::Unicode as LintPassObject);
     reg.register_lint_pass(box strings::StringAdd as LintPassObject);
     reg.register_lint_pass(box misc::NeedlessReturn as LintPassObject);
+    reg.register_lint_pass(box methods::MethodsPass as LintPassObject);
 
     reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
                                            misc::SINGLE_MATCH, misc::STR_TO_STRING,
@@ -77,5 +79,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
                                            strings::STRING_ADD_ASSIGN,
                                            misc::NEEDLESS_RETURN,
                                            misc::MODULO_ONE,
+                                           methods::OPTION_UNWRAP_USED,
+                                           methods::RESULT_UNWRAP_USED,
                                            ]);
 }
diff --git a/src/methods.rs b/src/methods.rs
new file mode 100644
index 00000000000..3d9aa8c6ffc
--- /dev/null
+++ b/src/methods.rs
@@ -0,0 +1,39 @@
+use syntax::ast::*;
+use rustc::lint::{Context, LintPass, LintArray};
+use rustc::middle::ty;
+
+use utils::{span_lint, match_def_path, walk_ptrs_ty};
+
+#[derive(Copy,Clone)]
+pub struct MethodsPass;
+
+declare_lint!(pub OPTION_UNWRAP_USED, Warn,
+              "Warn on using unwrap() on an Option value");
+declare_lint!(pub RESULT_UNWRAP_USED, Allow,
+              "Warn on using unwrap() on a Result value");
+
+impl LintPass for MethodsPass {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(OPTION_UNWRAP_USED, RESULT_UNWRAP_USED)
+    }
+
+    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
+        if let ExprMethodCall(ref ident, _, ref args) = expr.node {
+            if ident.node.name == "unwrap" {
+                if let ty::TyEnum(did, _) = walk_ptrs_ty(cx.tcx.expr_ty(&*args[0])).sty {
+                    if match_def_path(cx, did.did, &["core", "option", "Option"]) {
+                        span_lint(cx, OPTION_UNWRAP_USED, expr.span,
+                                  "used unwrap() on an Option value. If you don't want \
+                                   to handle the None case gracefully, consider using
+                                   expect() to provide a better panic message.");
+                    }
+                    else if match_def_path(cx, did.did, &["core", "result", "Result"]) {
+                        span_lint(cx, RESULT_UNWRAP_USED, expr.span,
+                                  "used unwrap() on a Result value. Graceful handling \
+                                   of Err values is preferred.");
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/tests/compile-fail/methods.rs b/tests/compile-fail/methods.rs
new file mode 100755
index 00000000000..e989dffe5a7
--- /dev/null
+++ b/tests/compile-fail/methods.rs
@@ -0,0 +1,11 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+
+#[deny(option_unwrap_used, result_unwrap_used)]
+fn main() {
+    let opt = Some(0);
+    let _ = opt.unwrap();  //~ERROR
+
+    let res: Result<i32, ()> = Ok(0);
+    let _ = res.unwrap();  //~ERROR
+}