Change to TryFrom

clippy_lints/src/fallible_impl_from.rs

@@ -3,12 +3,11 @@ use rustc::hir;
 use rustc::ty;
 use syntax_pos::Span;
 use utils::{method_chain_args, match_def_path, span_lint_and_then, walk_ptrs_ty};
-use utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT, STRING};
+use utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT};
 
-/// **What it does:** Checks for impls of `From<&str>` and `From<String>` that contain `panic!()` or
-/// `unwrap()`
+/// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
 ///
-/// **Why is this bad?** `FromStr` should be used if there's a possibility of failure.
+/// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
 ///
 /// **Known problems:** None.
 ///
@@ -22,19 +21,19 @@ use utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT, STR
 /// }
 /// ```
 declare_lint! {
-    pub IMPL_FROM_STR, Warn,
-    "Warn on impls of `From<&str>` and `From<String>` that contain `panic!()` or `unwrap()`"
+    pub FALLIBLE_IMPL_FROM, Allow,
+    "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
 }
 
-pub struct ImplFromStr;
+pub struct FallibleImplFrom;
 
-impl LintPass for ImplFromStr {
+impl LintPass for FallibleImplFrom {
     fn get_lints(&self) -> LintArray {
-        lint_array!(IMPL_FROM_STR)
+        lint_array!(FALLIBLE_IMPL_FROM)
     }
 }
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplFromStr {
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
         // check for `impl From<???> for ..`
         let impl_def_id = cx.tcx.hir.local_def_id(item.id);
@@ -43,15 +42,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplFromStr {
             let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id),
             match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT),
         ], {
-            // check if the type parameter is `str` or `String`
-            let from_ty_param = impl_trait_ref.substs.type_at(1);
-            let base_from_ty_param =
-                walk_ptrs_ty(cx.tcx.normalize_associated_type(&from_ty_param));
-            if base_from_ty_param.sty == ty::TyStr ||
-                match_type(cx.tcx, base_from_ty_param, &STRING)
-            {
-                lint_impl_body(cx, item.span, impl_items);
-            }
+            lint_impl_body(cx, item.span, impl_items);
         }}
     }
 }
@@ -117,10 +108,13 @@ fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_it
             if !fpu.result.is_empty() {
                 span_lint_and_then(
                     cx,
-                    IMPL_FROM_STR,
+                    FALLIBLE_IMPL_FROM,
                     impl_span,
-                    "consider implementing `FromStr` instead",
+                    "consider implementing `TryFrom` instead",
                     move |db| {
+                        db.help(
+                            "`From` is intended for infallible conversions only. \
+                             Use `TryFrom` if there's a possibility for the conversion to fail.");
                         db.span_note(fpu.result, "potential failure(s)");
                     });
             }

clippy_lints/src/lib.rs

@@ -100,7 +100,7 @@ pub mod identity_conversion;
 pub mod identity_op;
 pub mod if_let_redundant_pattern_matching;
 pub mod if_not_else;
-pub mod impl_from_str;
+pub mod fallible_impl_from;
 pub mod infinite_iter;
 pub mod int_plus_one;
 pub mod invalid_ref;
@@ -342,7 +342,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_late_lint_pass(box identity_conversion::IdentityConversion::default());
     reg.register_late_lint_pass(box types::ImplicitHasher);
     reg.register_early_lint_pass(box const_static_lifetime::StaticConst);
-    reg.register_late_lint_pass(box impl_from_str::ImplFromStr);
+    reg.register_late_lint_pass(box fallible_impl_from::FallibleImplFrom);
 
     reg.register_lint_group("clippy_restrictions", vec![
         arithmetic::FLOAT_ARITHMETIC,
@@ -448,7 +448,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         identity_conversion::IDENTITY_CONVERSION,
         identity_op::IDENTITY_OP,
         if_let_redundant_pattern_matching::IF_LET_REDUNDANT_PATTERN_MATCHING,
-        impl_from_str::IMPL_FROM_STR,
+        fallible_impl_from::FALLIBLE_IMPL_FROM,
         infinite_iter::INFINITE_ITER,
         invalid_ref::INVALID_REF,
         is_unit_expr::UNIT_EXPR,

tests/ui/fallible_impl_from.rs

@@ -1,3 +1,5 @@
+#![deny(fallible_impl_from)]
+
 // docs example
 struct Foo(i32);
 impl From<String> for Foo {
@@ -14,16 +16,8 @@ impl<'a> From<&'a str> for Valid {
         Valid(s.to_owned().into_bytes())
     }
 }
-impl From<String> for Valid {
-    fn from(s: String) -> Valid {
-        Valid(s.into_bytes())
-    }
-}
 impl From<usize> for Valid {
     fn from(i: usize) -> Valid {
-        if i == 0 {
-            panic!();
-        }
         Valid(Vec::with_capacity(i))
     }
 }
@@ -31,17 +25,18 @@ impl From<usize> for Valid {
 
 struct Invalid;
 
-impl<'a> From<&'a str> for Invalid {
-    fn from(s: &'a str) -> Invalid {
-        if !s.is_empty() {
+impl From<usize> for Invalid {
+    fn from(i: usize) -> Invalid {
+        if i != 42 {
             panic!();
         }
         Invalid
     }
 }
 
-impl From<String> for Invalid {
-    fn from(s: String) -> Invalid {
+impl From<Option<String>> for Invalid {
+    fn from(s: Option<String>) -> Invalid {
+        let s = s.unwrap();
         if !s.is_empty() {
             panic!(42);
         } else if s.parse::<u32>().unwrap() != 42 {

tests/ui/fallible_impl_from.stderr

@@ -0,0 +1,91 @@
+error: consider implementing `TryFrom` instead
+ --> $DIR/fallible_impl_from.rs:5:1
+  |
+5 | / impl From<String> for Foo {
+6 | |     fn from(s: String) -> Self {
+7 | |         Foo(s.parse().unwrap())
+8 | |     }
+9 | | }
+  | |_^
+  |
+note: lint level defined here
+ --> $DIR/fallible_impl_from.rs:1:9
+  |
+1 | #![deny(fallible_impl_from)]
+  |         ^^^^^^^^^^^^^^^^^^
+  = help: `From` is intended for infallible conversions only. Use `TryFrom` if there's a possibility for the conversion to fail.
+note: potential failure(s)
+ --> $DIR/fallible_impl_from.rs:7:13
+  |
+7 |         Foo(s.parse().unwrap())
+  |             ^^^^^^^^^^^^^^^^^^
+
+error: consider implementing `TryFrom` instead
+  --> $DIR/fallible_impl_from.rs:28:1
+   |
+28 | / impl From<usize> for Invalid {
+29 | |     fn from(i: usize) -> Invalid {
+30 | |         if i != 42 {
+31 | |             panic!();
+...  |
+34 | |     }
+35 | | }
+   | |_^
+   |
+   = help: `From` is intended for infallible conversions only. Use `TryFrom` if there's a possibility for the conversion to fail.
+note: potential failure(s)
+  --> $DIR/fallible_impl_from.rs:31:13
+   |
+31 |             panic!();
+   |             ^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate
+
+error: consider implementing `TryFrom` instead
+  --> $DIR/fallible_impl_from.rs:37:1
+   |
+37 | / impl From<Option<String>> for Invalid {
+38 | |     fn from(s: Option<String>) -> Invalid {
+39 | |         let s = s.unwrap();
+40 | |         if !s.is_empty() {
+...  |
+46 | |     }
+47 | | }
+   | |_^
+   |
+   = help: `From` is intended for infallible conversions only. Use `TryFrom` if there's a possibility for the conversion to fail.
+note: potential failure(s)
+  --> $DIR/fallible_impl_from.rs:39:17
+   |
+39 |         let s = s.unwrap();
+   |                 ^^^^^^^^^^
+40 |         if !s.is_empty() {
+41 |             panic!(42);
+   |             ^^^^^^^^^^^
+42 |         } else if s.parse::<u32>().unwrap() != 42 {
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^
+43 |             panic!("{:?}", s);
+   |             ^^^^^^^^^^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate
+
+error: consider implementing `TryFrom` instead
+  --> $DIR/fallible_impl_from.rs:55:1
+   |
+55 | / impl<'a> From<&'a mut <Box<u32> as ProjStrTrait>::ProjString> for Invalid {
+56 | |     fn from(s: &'a mut <Box<u32> as ProjStrTrait>::ProjString) -> Invalid {
+57 | |         if s.parse::<u32>().ok().unwrap() != 42 {
+58 | |             panic!("{:?}", s);
+...  |
+61 | |     }
+62 | | }
+   | |_^
+   |
+   = help: `From` is intended for infallible conversions only. Use `TryFrom` if there's a possibility for the conversion to fail.
+note: potential failure(s)
+  --> $DIR/fallible_impl_from.rs:57:12
+   |
+57 |         if s.parse::<u32>().ok().unwrap() != 42 {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+58 |             panic!("{:?}", s);
+   |             ^^^^^^^^^^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate
+

tests/ui/impl_from_str.stderr

@@ -1,80 +0,0 @@
-error: consider implementing `FromStr` instead
- --> $DIR/impl_from_str.rs:3:1
-  |
-3 | / impl From<String> for Foo {
-4 | |     fn from(s: String) -> Self {
-5 | |         Foo(s.parse().unwrap())
-6 | |     }
-7 | | }
-  | |_^
-  |
-  = note: `-D impl-from-str` implied by `-D warnings`
-note: potential failure(s)
- --> $DIR/impl_from_str.rs:5:13
-  |
-5 |         Foo(s.parse().unwrap())
-  |             ^^^^^^^^^^^^^^^^^^
-
-error: consider implementing `FromStr` instead
-  --> $DIR/impl_from_str.rs:34:1
-   |
-34 | / impl<'a> From<&'a str> for Invalid {
-35 | |     fn from(s: &'a str) -> Invalid {
-36 | |         if !s.is_empty() {
-37 | |             panic!();
-...  |
-40 | |     }
-41 | | }
-   | |_^
-   |
-note: potential failure(s)
-  --> $DIR/impl_from_str.rs:37:13
-   |
-37 |             panic!();
-   |             ^^^^^^^^^
-   = note: this error originates in a macro outside of the current crate
-
-error: consider implementing `FromStr` instead
-  --> $DIR/impl_from_str.rs:43:1
-   |
-43 | / impl From<String> for Invalid {
-44 | |     fn from(s: String) -> Invalid {
-45 | |         if !s.is_empty() {
-46 | |             panic!(42);
-...  |
-51 | |     }
-52 | | }
-   | |_^
-   |
-note: potential failure(s)
-  --> $DIR/impl_from_str.rs:46:13
-   |
-46 |             panic!(42);
-   |             ^^^^^^^^^^^
-47 |         } else if s.parse::<u32>().unwrap() != 42 {
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^
-48 |             panic!("{:?}", s);
-   |             ^^^^^^^^^^^^^^^^^^
-   = note: this error originates in a macro outside of the current crate
-
-error: consider implementing `FromStr` instead
-  --> $DIR/impl_from_str.rs:60:1
-   |
-60 | / impl<'a> From<&'a mut <Box<u32> as ProjStrTrait>::ProjString> for Invalid {
-61 | |     fn from(s: &'a mut <Box<u32> as ProjStrTrait>::ProjString) -> Invalid {
-62 | |         if s.parse::<u32>().ok().unwrap() != 42 {
-63 | |             panic!("{:?}", s);
-...  |
-66 | |     }
-67 | | }
-   | |_^
-   |
-note: potential failure(s)
-  --> $DIR/impl_from_str.rs:62:12
-   |
-62 |         if s.parse::<u32>().ok().unwrap() != 42 {
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-63 |             panic!("{:?}", s);
-   |             ^^^^^^^^^^^^^^^^^^
-   = note: this error originates in a macro outside of the current crate
-