Fix wrong suggestion in TRANSMUTE_PTR_TO_REF with lts

clippy_lints/src/transmute.rs

@@ -2,7 +2,7 @@ use rustc::lint::*;
 use rustc::ty::TypeVariants::{TyRawPtr, TyRef};
 use rustc::ty;
 use rustc::hir::*;
-use utils::{match_def_path, paths, span_lint, span_lint_and_then};
+use utils::{match_def_path, paths, span_lint, span_lint_and_then, snippet};
 use utils::sugg;
 
 /// **What it does:** Checks for transmutes that can't ever be correct on any
@@ -87,7 +87,7 @@ impl LintPass for Transmute {
 impl LateLintPass for Transmute {
     fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
         if let ExprCall(ref path_expr, ref args) = e.node {
-            if let ExprPath(None, _) = path_expr.node {
+            if let ExprPath(None, ref path) = path_expr.node {
                 let def_id = cx.tcx.expect_def(path_expr.id).def_id();
 
                 if match_def_path(cx, def_id, &paths::TRANSMUTE) {
@@ -170,11 +170,10 @@ impl LateLintPass for Transmute {
                                     ("&*", "*const")
                                 };
 
-
                                 let arg = if from_pty.ty == to_rty.ty {
                                     arg
                                 } else {
-                                    arg.as_ty(&format!("{} {}", cast, to_rty.ty))
+                                    arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, path, to_rty.ty)))
                                 };
 
                                 db.span_suggestion(e.span, "try", sugg::make_unop(deref, arg).to_string());
@@ -187,3 +186,19 @@ impl LateLintPass for Transmute {
         }
     }
 }
+
+/// Get the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is not available , use
+/// the type's `ToString` implementation. In weird cases it could lead to types with invalid `'_`
+/// lifetime, but it should be rare.
+fn get_type_snippet(cx: &LateContext, path: &Path, to_rty: ty::Ty) -> String {
+    if_let_chain!{[
+        let Some(seg) = path.segments.last(),
+        let PathParameters::AngleBracketedParameters(ref ang) = seg.parameters,
+        let Some(to_ty) = ang.types.get(1),
+        let TyRptr(_, ref to_ty) = to_ty.node,
+    ], {
+        return snippet(cx, to_ty.ty.span, &to_rty.to_string()).to_string();
+    }}
+
+    to_rty.to_string()
+}

tests/compile-fail/transmute.rs

@@ -1,6 +1,8 @@
 #![feature(plugin)]
 #![plugin(clippy)]
 
+#![allow(dead_code)]
+
 extern crate core;
 
 use std::mem::transmute as my_transmute;
@@ -83,6 +85,31 @@ unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
     let _: &T = &*(om as *const T);
 }
 
+#[deny(transmute_ptr_to_ref)]
+fn issue1231() {
+    struct Foo<'a, T: 'a> {
+        bar: &'a T,
+    }
+
+    let raw = 0 as *const i32;
+    let _: &Foo<u8> = unsafe { std::mem::transmute::<_, &Foo<_>>(raw) };
+    //~^ ERROR transmute from a pointer type
+    //~| HELP try
+    //~| SUGGESTION unsafe { &*(raw as *const Foo<_>) };
+
+    let _: &Foo<&u8> = unsafe { std::mem::transmute::<_, &Foo<&_>>(raw) };
+    //~^ ERROR transmute from a pointer type
+    //~| HELP try
+    //~| SUGGESTION unsafe { &*(raw as *const Foo<&_>) };
+
+    type Bar<'a> = &'a u8;
+    let raw = 0 as *const i32;
+    unsafe { std::mem::transmute::<_, Bar>(raw) };
+    //~^ ERROR transmute from a pointer type
+    //~| HELP try
+    //~| SUGGESTION unsafe { &*(raw as *const u8) };
+}
+
 #[deny(useless_transmute)]
 fn useless() {
     unsafe {
@@ -144,7 +171,4 @@ fn crosspointer() {
     }
 }
 
-fn main() {
-    useless();
-    crosspointer();
-}
+fn main() { }