rust-clippy/clippy_lints/src/shadow.rs
2017-05-12 12:02:42 +02:00

395 lines
13 KiB
Rust

use reexport::*;
use rustc::lint::*;
use rustc::hir::*;
use rustc::hir::intravisit::{Visitor, FnKind, NestedVisitorMap};
use rustc::ty;
use syntax::codemap::Span;
use utils::{higher, in_external_macro, snippet, span_lint_and_then, iter_input_pats};
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, while just changing reference level or mutability.
///
/// **Why is this bad?** Not much, in fact it's a very common pattern in Rust
/// code. Still, some may opt to avoid it in their code base, they can set this
/// lint to `Warn`.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// let x = &x;
/// ```
declare_lint! {
pub SHADOW_SAME,
Allow,
"rebinding a name to itself, e.g. `let mut x = &mut x`"
}
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, while reusing the original value.
///
/// **Why is this bad?** Not too much, in fact it's a common pattern in Rust
/// code. Still, some argue that name shadowing like this hurts readability,
/// because a value may be bound to different things depending on position in
/// the code.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// let x = x + 1;
/// ```
declare_lint! {
pub SHADOW_REUSE,
Allow,
"rebinding a name to an expression that re-uses the original value, e.g. \
`let x = x + 1`"
}
/// **What it does:** Checks for bindings that shadow other bindings already in
/// scope, either without a initialization or with one that does not even use
/// the original value.
///
/// **Why is this bad?** Name shadowing can hurt readability, especially in
/// large code bases, because it is easy to lose track of the active binding at
/// any place in the code. This can be alleviated by either giving more specific
/// names to bindings ore introducing more scopes to contain the bindings.
///
/// **Known problems:** This lint, as the other shadowing related lints,
/// currently only catches very simple patterns.
///
/// **Example:**
/// ```rust
/// let x = y; let x = z; // shadows the earlier binding
/// ```
declare_lint! {
pub SHADOW_UNRELATED,
Allow,
"rebinding a name without even using the original value"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(SHADOW_SAME, SHADOW_REUSE, SHADOW_UNRELATED)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_fn(
&mut self,
cx: &LateContext<'a, 'tcx>,
_: FnKind<'tcx>,
decl: &'tcx FnDecl,
body: &'tcx Body,
_: Span,
_: NodeId
) {
if in_external_macro(cx, body.value.span) {
return;
}
check_fn(cx, decl, body);
}
}
fn check_fn<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, decl: &'tcx FnDecl, body: &'tcx Body) {
let mut bindings = Vec::new();
for arg in iter_input_pats(decl, body) {
if let PatKind::Binding(_, _, ident, _) = arg.pat.node {
bindings.push((ident.node, ident.span))
}
}
check_expr(cx, &body.value, &mut bindings);
}
fn check_block<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, block: &'tcx Block, bindings: &mut Vec<(Name, Span)>) {
let len = bindings.len();
for stmt in &block.stmts {
match stmt.node {
StmtDecl(ref decl, _) => check_decl(cx, decl, bindings),
StmtExpr(ref e, _) |
StmtSemi(ref e, _) => check_expr(cx, e, bindings),
}
}
if let Some(ref o) = block.expr {
check_expr(cx, o, bindings);
}
bindings.truncate(len);
}
fn check_decl<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, decl: &'tcx Decl, bindings: &mut Vec<(Name, Span)>) {
if in_external_macro(cx, decl.span) {
return;
}
if higher::is_from_for_desugar(decl) {
return;
}
if let DeclLocal(ref local) = decl.node {
let Local { ref pat, ref ty, ref init, span, .. } = **local;
if let Some(ref t) = *ty {
check_ty(cx, t, bindings)
}
if let Some(ref o) = *init {
check_expr(cx, o, bindings);
check_pat(cx, pat, Some(o), span, bindings);
} else {
check_pat(cx, pat, None, span, bindings);
}
}
}
fn is_binding(cx: &LateContext, pat_id: NodeId) -> bool {
let var_ty = cx.tables.node_id_to_type(pat_id);
match var_ty.sty {
ty::TyAdt(..) => false,
_ => true,
}
}
fn check_pat<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
pat: &'tcx Pat,
init: Option<&'tcx Expr>,
span: Span,
bindings: &mut Vec<(Name, Span)>
) {
// TODO: match more stuff / destructuring
match pat.node {
PatKind::Binding(_, _, ref ident, ref inner) => {
let name = ident.node;
if is_binding(cx, pat.id) {
let mut new_binding = true;
for tup in bindings.iter_mut() {
if tup.0 == name {
lint_shadow(cx, name, span, pat.span, init, tup.1);
tup.1 = ident.span;
new_binding = false;
break;
}
}
if new_binding {
bindings.push((name, ident.span));
}
}
if let Some(ref p) = *inner {
check_pat(cx, p, init, span, bindings);
}
},
PatKind::Struct(_, ref pfields, _) => {
if let Some(init_struct) = init {
if let ExprStruct(_, ref efields, _) = init_struct.node {
for field in pfields {
let name = field.node.name;
let efield = efields.iter()
.find(|f| f.name.node == name)
.map(|f| &*f.expr);
check_pat(cx, &field.node.pat, efield, span, bindings);
}
} else {
for field in pfields {
check_pat(cx, &field.node.pat, init, span, bindings);
}
}
} else {
for field in pfields {
check_pat(cx, &field.node.pat, None, span, bindings);
}
}
},
PatKind::Tuple(ref inner, _) => {
if let Some(init_tup) = init {
if let ExprTup(ref tup) = init_tup.node {
for (i, p) in inner.iter().enumerate() {
check_pat(cx, p, Some(&tup[i]), p.span, bindings);
}
} else {
for p in inner {
check_pat(cx, p, init, span, bindings);
}
}
} else {
for p in inner {
check_pat(cx, p, None, span, bindings);
}
}
},
PatKind::Box(ref inner) => {
if let Some(initp) = init {
if let ExprBox(ref inner_init) = initp.node {
check_pat(cx, inner, Some(&**inner_init), span, bindings);
} else {
check_pat(cx, inner, init, span, bindings);
}
} else {
check_pat(cx, inner, init, span, bindings);
}
},
PatKind::Ref(ref inner, _) => check_pat(cx, inner, init, span, bindings),
// PatVec(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
_ => (),
}
}
fn lint_shadow<'a, 'tcx: 'a>(
cx: &LateContext<'a, 'tcx>,
name: Name,
span: Span,
pattern_span: Span,
init: Option<&'tcx Expr>,
prev_span: Span
) {
if let Some(expr) = init {
if is_self_shadow(name, expr) {
span_lint_and_then(cx,
SHADOW_SAME,
span,
&format!("`{}` is shadowed by itself in `{}`",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")),
|db| { db.span_note(prev_span, "previous binding is here"); });
} else if contains_self(name, expr) {
span_lint_and_then(cx,
SHADOW_REUSE,
pattern_span,
&format!("`{}` is shadowed by `{}` which reuses the original value",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")),
|db| {
db.span_note(expr.span, "initialization happens here");
db.span_note(prev_span, "previous binding is here");
});
} else {
span_lint_and_then(cx,
SHADOW_UNRELATED,
pattern_span,
&format!("`{}` is shadowed by `{}`",
snippet(cx, pattern_span, "_"),
snippet(cx, expr.span, "..")),
|db| {
db.span_note(expr.span, "initialization happens here");
db.span_note(prev_span, "previous binding is here");
});
}
} else {
span_lint_and_then(cx,
SHADOW_UNRELATED,
span,
&format!("`{}` shadows a previous declaration", snippet(cx, pattern_span, "_")),
|db| { db.span_note(prev_span, "previous binding is here"); });
}
}
fn check_expr<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, bindings: &mut Vec<(Name, Span)>) {
if in_external_macro(cx, expr.span) {
return;
}
match expr.node {
ExprUnary(_, ref e) |
ExprField(ref e, _) |
ExprTupField(ref e, _) |
ExprAddrOf(_, ref e) |
ExprBox(ref e) => check_expr(cx, e, bindings),
ExprBlock(ref block) |
ExprLoop(ref block, _, _) => check_block(cx, block, bindings),
// ExprCall
// ExprMethodCall
ExprArray(ref v) | ExprTup(ref v) => {
for e in v {
check_expr(cx, e, bindings)
}
},
ExprIf(ref cond, ref then, ref otherwise) => {
check_expr(cx, cond, bindings);
check_expr(cx, &**then, bindings);
if let Some(ref o) = *otherwise {
check_expr(cx, o, bindings);
}
},
ExprWhile(ref cond, ref block, _) => {
check_expr(cx, cond, bindings);
check_block(cx, block, bindings);
},
ExprMatch(ref init, ref arms, _) => {
check_expr(cx, init, bindings);
let len = bindings.len();
for arm in arms {
for pat in &arm.pats {
check_pat(cx, pat, Some(&**init), pat.span, bindings);
// This is ugly, but needed to get the right type
if let Some(ref guard) = arm.guard {
check_expr(cx, guard, bindings);
}
check_expr(cx, &arm.body, bindings);
bindings.truncate(len);
}
}
},
_ => (),
}
}
fn check_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: &'tcx Ty, bindings: &mut Vec<(Name, Span)>) {
match ty.node {
TySlice(ref sty) => check_ty(cx, sty, bindings),
TyArray(ref fty, body_id) => {
check_ty(cx, fty, bindings);
check_expr(cx, &cx.tcx.hir.body(body_id).value, bindings);
},
TyPtr(MutTy { ty: ref mty, .. }) |
TyRptr(_, MutTy { ty: ref mty, .. }) => check_ty(cx, mty, bindings),
TyTup(ref tup) => {
for t in tup {
check_ty(cx, t, bindings)
}
},
TyTypeof(body_id) => check_expr(cx, &cx.tcx.hir.body(body_id).value, bindings),
_ => (),
}
}
fn is_self_shadow(name: Name, expr: &Expr) -> bool {
match expr.node {
ExprBox(ref inner) |
ExprAddrOf(_, ref inner) => is_self_shadow(name, inner),
ExprBlock(ref block) => {
block.stmts.is_empty() && block.expr.as_ref().map_or(false, |e| is_self_shadow(name, e))
},
ExprUnary(op, ref inner) => (UnDeref == op) && is_self_shadow(name, inner),
ExprPath(QPath::Resolved(_, ref path)) => path_eq_name(name, path),
_ => false,
}
}
fn path_eq_name(name: Name, path: &Path) -> bool {
!path.is_global() && path.segments.len() == 1 && path.segments[0].name.as_str() == name.as_str()
}
struct ContainsSelf {
name: Name,
result: bool,
}
impl<'tcx> Visitor<'tcx> for ContainsSelf {
fn visit_name(&mut self, _: Span, name: Name) {
if self.name == name {
self.result = true;
}
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn contains_self(name: Name, expr: &Expr) -> bool {
let mut cs = ContainsSelf {
name: name,
result: false,
};
cs.visit_expr(expr);
cs.result
}