Make deref_nullptr deny by default instead of warn

Author: saethlin

compiler/rustc_lint/src/builtin.rs

@@ -2697,7 +2697,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,no_run
+    /// ```rust,compile_fail
     /// # #![allow(unused)]
     /// use std::ptr;
     /// unsafe {
@@ -2716,7 +2716,7 @@ declare_lint! {
     ///
     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
     pub DEREF_NULLPTR,
-    Warn,
+    Deny,
     "detects when an null pointer is dereferenced"
 }
 

tests/ui/lint/lint-forbid-internal-unsafe.rs

@@ -13,5 +13,5 @@ macro_rules! evil {
 
 fn main() {
     println!("{}", evil!(*(0 as *const u8)));
-    //~^ WARNING dereferencing a null pointer
+    //~^ ERROR dereferencing a null pointer
 }

tests/ui/lint/lint-forbid-internal-unsafe.stderr

@@ -10,13 +10,13 @@ note: the lint level is defined here
 LL | #![forbid(unsafe_code)]
    |           ^^^^^^^^^^^
 
-warning: dereferencing a null pointer
+error: dereferencing a null pointer
   --> $DIR/lint-forbid-internal-unsafe.rs:15:26
    |
 LL |     println!("{}", evil!(*(0 as *const u8)));
    |                          ^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
    |
-   = note: `#[warn(deref_nullptr)]` on by default
+   = note: `#[deny(deref_nullptr)]` on by default
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors
 

tests/ui/unreachable-code/unreachable-bool-read-7246.rs

@@ -5,7 +5,7 @@ use std::ptr;
 pub unsafe fn g() {
     return;
     if *ptr::null() {}; //~ ERROR unreachable
-    //~| WARNING dereferencing a null pointer
+    //~| ERROR dereferencing a null pointer
 }
 
 pub fn main() {}

tests/ui/unreachable-code/unreachable-bool-read-7246.stderr

@@ -12,13 +12,13 @@ note: the lint level is defined here
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
 
-warning: dereferencing a null pointer
+error: dereferencing a null pointer
   --> $DIR/unreachable-bool-read-7246.rs:7:8
    |
 LL |     if *ptr::null() {};
    |        ^^^^^^^^^^^^ this code causes undefined behavior when executed
    |
-   = note: `#[warn(deref_nullptr)]` on by default
+   = note: `#[deny(deref_nullptr)]` on by default
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors