Auto merge of rust-lang#5081 - Areredify:vec_box_threshold, r=flip1995

add size parameter for `vec_box`  lint

changelog: add size threshold for the `vec_box` lint, currently 4096 bytes (one page) (subject to change). Closes rust-lang#3547.

diff is a little bit confusing due to some refactoring (moving free functions to lint struct functions), relevant portion is [this](https://github.com/rust-lang/rust-clippy/compare/master...Areredify:vec_box_threshold?expand=1#diff-1096120ca9143af89dcc9175ea92b54aR294-R298). In hindsight should've been different commits, but oh well.

Author: bors

clippy_lints/src/lib.rs

@@ -819,7 +819,8 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| box utils::internal_lints::OuterExpnDataPass);
     store.register_late_pass(|| box utils::inspector::DeepCodeInspector);
     store.register_late_pass(|| box utils::author::Author);
-    store.register_late_pass(|| box types::Types);
+    let vec_box_size_threshold = conf.vec_box_size_threshold;
+    store.register_late_pass(move || box types::Types::new(vec_box_size_threshold));
     store.register_late_pass(|| box booleans::NonminimalBool);
     store.register_late_pass(|| box eq_op::EqOp);
     store.register_late_pass(|| box enum_glob_use::EnumGlobUse);

clippy_lints/src/types.rs

@@ -152,6 +152,8 @@ define_Conf! {
     (too_many_lines_threshold, "too_many_lines_threshold", 100 => u64),
     /// Lint: LARGE_STACK_ARRAYS. The maximum allowed size for arrays on the stack
     (array_size_threshold, "array_size_threshold", 512_000 => u64),
+    /// Lint: VEC_BOX. The size of the boxed type in bytes, where boxing in a `Vec` is allowed
+    (vec_box_size_threshold, "vec_box_size_threshold", 4096 => u64),
 }
 
 impl Default for Conf {

clippy_lints/src/utils/conf.rs

@@ -1,4 +1,4 @@
-error: error reading Clippy's configuration file `$DIR/clippy.toml`: unknown field `foobar`, expected one of `blacklisted-names`, `cognitive-complexity-threshold`, `cyclomatic-complexity-threshold`, `doc-valid-idents`, `too-many-arguments-threshold`, `type-complexity-threshold`, `single-char-binding-names-threshold`, `too-large-for-stack`, `enum-variant-name-threshold`, `enum-variant-size-threshold`, `verbose-bit-mask-threshold`, `literal-representation-threshold`, `trivial-copy-size-limit`, `too-many-lines-threshold`, `array-size-threshold`, `third-party` at line 5 column 1
+error: error reading Clippy's configuration file `$DIR/clippy.toml`: unknown field `foobar`, expected one of `blacklisted-names`, `cognitive-complexity-threshold`, `cyclomatic-complexity-threshold`, `doc-valid-idents`, `too-many-arguments-threshold`, `type-complexity-threshold`, `single-char-binding-names-threshold`, `too-large-for-stack`, `enum-variant-name-threshold`, `enum-variant-size-threshold`, `verbose-bit-mask-threshold`, `literal-representation-threshold`, `trivial-copy-size-limit`, `too-many-lines-threshold`, `array-size-threshold`, `vec-box-size-threshold`, `third-party` at line 5 column 1
 
 error: aborting due to previous error
 

tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr

@@ -0,0 +1 @@
+vec-box-size-threshold = 4

tests/ui-toml/vec_box_sized/clippy.toml

@@ -0,0 +1,15 @@
+struct S {
+    x: u64,
+}
+
+struct C {
+    y: u16,
+}
+
+struct Foo(Vec<Box<u8>>);
+struct Bar(Vec<Box<u32>>);
+struct Baz(Vec<Box<(u32, u32)>>);
+struct BarBaz(Vec<Box<S>>);
+struct FooBarBaz(Vec<Box<C>>);
+
+fn main() {}

tests/ui-toml/vec_box_sized/test.rs

@@ -0,0 +1,22 @@
+error: `Vec<T>` is already on the heap, the boxing is unnecessary.
+  --> $DIR/test.rs:9:12
+   |
+LL | struct Foo(Vec<Box<u8>>);
+   |            ^^^^^^^^^^^^ help: try: `Vec<u8>`
+   |
+   = note: `-D clippy::vec-box` implied by `-D warnings`
+
+error: `Vec<T>` is already on the heap, the boxing is unnecessary.
+  --> $DIR/test.rs:10:12
+   |
+LL | struct Bar(Vec<Box<u32>>);
+   |            ^^^^^^^^^^^^^ help: try: `Vec<u32>`
+
+error: `Vec<T>` is already on the heap, the boxing is unnecessary.
+  --> $DIR/test.rs:13:18
+   |
+LL | struct FooBarBaz(Vec<Box<C>>);
+   |                  ^^^^^^^^^^^ help: try: `Vec<C>`
+
+error: aborting due to 3 previous errors
+

tests/ui-toml/vec_box_sized/test.stderr

@@ -4,6 +4,7 @@
 
 struct SizedStruct(i32);
 struct UnsizedStruct([i32]);
+struct BigStruct([i32; 10000]);
 
 /// The following should trigger the lint
 mod should_trigger {
@@ -19,9 +20,10 @@ mod should_trigger {
 
 /// The following should not trigger the lint
 mod should_not_trigger {
-    use super::UnsizedStruct;
+    use super::{BigStruct, UnsizedStruct};
 
     struct C(Vec<Box<UnsizedStruct>>);
+    struct D(Vec<Box<BigStruct>>);
 
     struct StructWithVecBoxButItsUnsized {
         unsized_type: Vec<Box<UnsizedStruct>>,

tests/ui/vec_box_sized.fixed

@@ -4,6 +4,7 @@
 
 struct SizedStruct(i32);
 struct UnsizedStruct([i32]);
+struct BigStruct([i32; 10000]);
 
 /// The following should trigger the lint
 mod should_trigger {
@@ -19,9 +20,10 @@ mod should_trigger {
 
 /// The following should not trigger the lint
 mod should_not_trigger {
-    use super::UnsizedStruct;
+    use super::{BigStruct, UnsizedStruct};
 
     struct C(Vec<Box<UnsizedStruct>>);
+    struct D(Vec<Box<BigStruct>>);
 
     struct StructWithVecBoxButItsUnsized {
         unsized_type: Vec<Box<UnsizedStruct>>,

tests/ui/vec_box_sized.rs

@@ -1,19 +1,19 @@
 error: `Vec<T>` is already on the heap, the boxing is unnecessary.
-  --> $DIR/vec_box_sized.rs:13:21
+  --> $DIR/vec_box_sized.rs:14:21
    |
 LL |         sized_type: Vec<Box<SizedStruct>>,
    |                     ^^^^^^^^^^^^^^^^^^^^^ help: try: `Vec<SizedStruct>`
    |
    = note: `-D clippy::vec-box` implied by `-D warnings`
 
 error: `Vec<T>` is already on the heap, the boxing is unnecessary.
-  --> $DIR/vec_box_sized.rs:16:14
+  --> $DIR/vec_box_sized.rs:17:14
    |
 LL |     struct A(Vec<Box<SizedStruct>>);
    |              ^^^^^^^^^^^^^^^^^^^^^ help: try: `Vec<SizedStruct>`
 
 error: `Vec<T>` is already on the heap, the boxing is unnecessary.
-  --> $DIR/vec_box_sized.rs:17:18
+  --> $DIR/vec_box_sized.rs:18:18
    |
 LL |     struct B(Vec<Vec<Box<(u32)>>>);
    |                  ^^^^^^^^^^^^^^^ help: try: `Vec<u32>`