Auto merge of rust-lang#5667 - djugei:master, r=flip1995

moved cast_ptr_alignment to pedantic and expanded documentation

fixes: rust-lang#5618
changelog: cast_ptr_alignment moved to pedantic

Author: bors

clippy_lints/src/lib.rs

@@ -1167,6 +1167,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&types::CAST_POSSIBLE_TRUNCATION),
         LintId::of(&types::CAST_POSSIBLE_WRAP),
         LintId::of(&types::CAST_PRECISION_LOSS),
+        LintId::of(&types::CAST_PTR_ALIGNMENT),
         LintId::of(&types::CAST_SIGN_LOSS),
         LintId::of(&types::IMPLICIT_HASHER),
         LintId::of(&types::INVALID_UPCAST_COMPARISONS),
@@ -1413,7 +1414,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&types::ABSURD_EXTREME_COMPARISONS),
         LintId::of(&types::BORROWED_BOX),
         LintId::of(&types::BOX_VEC),
-        LintId::of(&types::CAST_PTR_ALIGNMENT),
         LintId::of(&types::CAST_REF_TO_MUT),
         LintId::of(&types::CHAR_LIT_AS_U8),
         LintId::of(&types::FN_TO_NUMERIC_CAST),
@@ -1673,7 +1673,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&transmute::WRONG_TRANSMUTE),
         LintId::of(&transmuting_null::TRANSMUTING_NULL),
         LintId::of(&types::ABSURD_EXTREME_COMPARISONS),
-        LintId::of(&types::CAST_PTR_ALIGNMENT),
         LintId::of(&types::CAST_REF_TO_MUT),
         LintId::of(&types::UNIT_CMP),
         LintId::of(&unicode::ZERO_WIDTH_SPACE),

clippy_lints/src/types.rs

@@ -974,15 +974,16 @@ declare_clippy_lint! {
     /// behavior.
     ///
     /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
-    /// on the resulting pointer is fine.
+    /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
+    /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
     ///
     /// **Example:**
     /// ```rust
     /// let _ = (&1u8 as *const u8) as *const u16;
     /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
     /// ```
     pub CAST_PTR_ALIGNMENT,
-    correctness,
+    pedantic,
     "cast from a pointer to a more-strictly-aligned pointer"
 }
 

src/lintlist/mod.rs

@@ -166,7 +166,7 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     },
     Lint {
         name: "cast_ptr_alignment",
-        group: "correctness",
+        group: "pedantic",
         desc: "cast from a pointer to a more-strictly-aligned pointer",
         deprecation: None,
         module: "types",