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copies.rs
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copies.rs
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use clippy_utils::diagnostics::{span_lint_and_note, span_lint_and_then};
use clippy_utils::source::{first_line_of_span, indent_of, reindent_multiline, snippet, snippet_opt};
use clippy_utils::{
both, count_eq, eq_expr_value, get_enclosing_block, get_parent_expr, if_sequence, in_macro, is_else_clause,
is_lint_allowed, search_same, ContainsName, SpanlessEq, SpanlessHash,
};
use if_chain::if_chain;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::{Applicability, DiagnosticBuilder};
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::{Block, Expr, ExprKind, HirId};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::hir::map::Map;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{source_map::Span, symbol::Symbol, BytePos};
use std::borrow::Cow;
declare_clippy_lint! {
/// ### What it does
/// Checks for consecutive `if`s with the same condition.
///
/// ### Why is this bad?
/// This is probably a copy & paste error.
///
/// ### Example
/// ```ignore
/// if a == b {
/// …
/// } else if a == b {
/// …
/// }
/// ```
///
/// Note that this lint ignores all conditions with a function call as it could
/// have side effects:
///
/// ```ignore
/// if foo() {
/// …
/// } else if foo() { // not linted
/// …
/// }
/// ```
pub IFS_SAME_COND,
correctness,
"consecutive `if`s with the same condition"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for consecutive `if`s with the same function call.
///
/// ### Why is this bad?
/// This is probably a copy & paste error.
/// Despite the fact that function can have side effects and `if` works as
/// intended, such an approach is implicit and can be considered a "code smell".
///
/// ### Example
/// ```ignore
/// if foo() == bar {
/// …
/// } else if foo() == bar {
/// …
/// }
/// ```
///
/// This probably should be:
/// ```ignore
/// if foo() == bar {
/// …
/// } else if foo() == baz {
/// …
/// }
/// ```
///
/// or if the original code was not a typo and called function mutates a state,
/// consider move the mutation out of the `if` condition to avoid similarity to
/// a copy & paste error:
///
/// ```ignore
/// let first = foo();
/// if first == bar {
/// …
/// } else {
/// let second = foo();
/// if second == bar {
/// …
/// }
/// }
/// ```
pub SAME_FUNCTIONS_IN_IF_CONDITION,
pedantic,
"consecutive `if`s with the same function call"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for `if/else` with the same body as the *then* part
/// and the *else* part.
///
/// ### Why is this bad?
/// This is probably a copy & paste error.
///
/// ### Example
/// ```ignore
/// let foo = if … {
/// 42
/// } else {
/// 42
/// };
/// ```
pub IF_SAME_THEN_ELSE,
correctness,
"`if` with the same `then` and `else` blocks"
}
declare_clippy_lint! {
/// ### What it does
/// Checks if the `if` and `else` block contain shared code that can be
/// moved out of the blocks.
///
/// ### Why is this bad?
/// Duplicate code is less maintainable.
///
/// ### Known problems
/// * The lint doesn't check if the moved expressions modify values that are beeing used in
/// the if condition. The suggestion can in that case modify the behavior of the program.
/// See [rust-clippy#7452](https://github.com/rust-lang/rust-clippy/issues/7452)
///
/// ### Example
/// ```ignore
/// let foo = if … {
/// println!("Hello World");
/// 13
/// } else {
/// println!("Hello World");
/// 42
/// };
/// ```
///
/// Could be written as:
/// ```ignore
/// println!("Hello World");
/// let foo = if … {
/// 13
/// } else {
/// 42
/// };
/// ```
pub BRANCHES_SHARING_CODE,
nursery,
"`if` statement with shared code in all blocks"
}
declare_lint_pass!(CopyAndPaste => [
IFS_SAME_COND,
SAME_FUNCTIONS_IN_IF_CONDITION,
IF_SAME_THEN_ELSE,
BRANCHES_SHARING_CODE
]);
impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if !expr.span.from_expansion() {
if let ExprKind::If(_, _, _) = expr.kind {
// skip ifs directly in else, it will be checked in the parent if
if let Some(&Expr {
kind: ExprKind::If(_, _, Some(else_expr)),
..
}) = get_parent_expr(cx, expr)
{
if else_expr.hir_id == expr.hir_id {
return;
}
}
let (conds, blocks) = if_sequence(expr);
// Conditions
lint_same_cond(cx, &conds);
lint_same_fns_in_if_cond(cx, &conds);
// Block duplication
lint_same_then_else(cx, &blocks, conds.len() == blocks.len(), expr);
}
}
}
}
/// Implementation of `BRANCHES_SHARING_CODE` and `IF_SAME_THEN_ELSE` if the blocks are equal.
fn lint_same_then_else<'tcx>(
cx: &LateContext<'tcx>,
blocks: &[&Block<'tcx>],
has_conditional_else: bool,
expr: &'tcx Expr<'_>,
) {
// We only lint ifs with multiple blocks
if blocks.len() < 2 || is_else_clause(cx.tcx, expr) {
return;
}
// Check if each block has shared code
let has_expr = blocks[0].expr.is_some();
let (start_eq, mut end_eq, expr_eq) = if let Some(block_eq) = scan_block_for_eq(cx, blocks) {
(block_eq.start_eq, block_eq.end_eq, block_eq.expr_eq)
} else {
return;
};
// BRANCHES_SHARING_CODE prerequisites
if has_conditional_else || (start_eq == 0 && end_eq == 0 && (has_expr && !expr_eq)) {
return;
}
// Only the start is the same
if start_eq != 0 && end_eq == 0 && (!has_expr || !expr_eq) {
let block = blocks[0];
let start_stmts = block.stmts.split_at(start_eq).0;
let mut start_walker = UsedValueFinderVisitor::new(cx);
for stmt in start_stmts {
intravisit::walk_stmt(&mut start_walker, stmt);
}
emit_branches_sharing_code_lint(
cx,
start_eq,
0,
false,
check_for_warn_of_moved_symbol(cx, &start_walker.def_symbols, expr),
blocks,
expr,
);
} else if end_eq != 0 || (has_expr && expr_eq) {
let block = blocks[blocks.len() - 1];
let (start_stmts, block_stmts) = block.stmts.split_at(start_eq);
let (block_stmts, end_stmts) = block_stmts.split_at(block_stmts.len() - end_eq);
// Scan start
let mut start_walker = UsedValueFinderVisitor::new(cx);
for stmt in start_stmts {
intravisit::walk_stmt(&mut start_walker, stmt);
}
let mut moved_syms = start_walker.def_symbols;
// Scan block
let mut block_walker = UsedValueFinderVisitor::new(cx);
for stmt in block_stmts {
intravisit::walk_stmt(&mut block_walker, stmt);
}
let mut block_defs = block_walker.defs;
// Scan moved stmts
let mut moved_start: Option<usize> = None;
let mut end_walker = UsedValueFinderVisitor::new(cx);
for (index, stmt) in end_stmts.iter().enumerate() {
intravisit::walk_stmt(&mut end_walker, stmt);
for value in &end_walker.uses {
// Well we can't move this and all prev statements. So reset
if block_defs.contains(value) {
moved_start = Some(index + 1);
end_walker.defs.drain().for_each(|x| {
block_defs.insert(x);
});
end_walker.def_symbols.clear();
}
}
end_walker.uses.clear();
}
if let Some(moved_start) = moved_start {
end_eq -= moved_start;
}
let end_linable = block.expr.map_or_else(
|| end_eq != 0,
|expr| {
intravisit::walk_expr(&mut end_walker, expr);
end_walker.uses.iter().any(|x| !block_defs.contains(x))
},
);
if end_linable {
end_walker.def_symbols.drain().for_each(|x| {
moved_syms.insert(x);
});
}
emit_branches_sharing_code_lint(
cx,
start_eq,
end_eq,
end_linable,
check_for_warn_of_moved_symbol(cx, &moved_syms, expr),
blocks,
expr,
);
}
}
struct BlockEqual {
/// The amount statements that are equal from the start
start_eq: usize,
/// The amount statements that are equal from the end
end_eq: usize,
/// An indication if the block expressions are the same. This will also be true if both are
/// `None`
expr_eq: bool,
}
/// This function can also trigger the `IF_SAME_THEN_ELSE` in which case it'll return `None` to
/// abort any further processing and avoid duplicate lint triggers.
fn scan_block_for_eq(cx: &LateContext<'tcx>, blocks: &[&Block<'tcx>]) -> Option<BlockEqual> {
let mut start_eq = usize::MAX;
let mut end_eq = usize::MAX;
let mut expr_eq = true;
let mut iter = blocks.windows(2);
while let Some(&[win0, win1]) = iter.next() {
let l_stmts = win0.stmts;
let r_stmts = win1.stmts;
// `SpanlessEq` now keeps track of the locals and is therefore context sensitive clippy#6752.
// The comparison therefore needs to be done in a way that builds the correct context.
let mut evaluator = SpanlessEq::new(cx);
let mut evaluator = evaluator.inter_expr();
let current_start_eq = count_eq(&mut l_stmts.iter(), &mut r_stmts.iter(), |l, r| evaluator.eq_stmt(l, r));
let current_end_eq = {
// We skip the middle statements which can't be equal
let end_comparison_count = l_stmts.len().min(r_stmts.len()) - current_start_eq;
let it1 = l_stmts.iter().skip(l_stmts.len() - end_comparison_count);
let it2 = r_stmts.iter().skip(r_stmts.len() - end_comparison_count);
it1.zip(it2)
.fold(0, |acc, (l, r)| if evaluator.eq_stmt(l, r) { acc + 1 } else { 0 })
};
let block_expr_eq = both(&win0.expr, &win1.expr, |l, r| evaluator.eq_expr(l, r));
// IF_SAME_THEN_ELSE
if_chain! {
if block_expr_eq;
if l_stmts.len() == r_stmts.len();
if l_stmts.len() == current_start_eq;
if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, win0.hir_id);
if !is_lint_allowed(cx, IF_SAME_THEN_ELSE, win1.hir_id);
then {
span_lint_and_note(
cx,
IF_SAME_THEN_ELSE,
win0.span,
"this `if` has identical blocks",
Some(win1.span),
"same as this",
);
return None;
}
}
start_eq = start_eq.min(current_start_eq);
end_eq = end_eq.min(current_end_eq);
expr_eq &= block_expr_eq;
}
if !expr_eq {
end_eq = 0;
}
// Check if the regions are overlapping. Set `end_eq` to prevent the overlap
let min_block_size = blocks.iter().map(|x| x.stmts.len()).min().unwrap();
if (start_eq + end_eq) > min_block_size {
end_eq = min_block_size - start_eq;
}
Some(BlockEqual {
start_eq,
end_eq,
expr_eq,
})
}
fn check_for_warn_of_moved_symbol(
cx: &LateContext<'tcx>,
symbols: &FxHashSet<Symbol>,
if_expr: &'tcx Expr<'_>,
) -> bool {
get_enclosing_block(cx, if_expr.hir_id).map_or(false, |block| {
let ignore_span = block.span.shrink_to_lo().to(if_expr.span);
symbols
.iter()
.filter(|sym| !sym.as_str().starts_with('_'))
.any(move |sym| {
let mut walker = ContainsName {
name: *sym,
result: false,
};
// Scan block
block
.stmts
.iter()
.filter(|stmt| !ignore_span.overlaps(stmt.span))
.for_each(|stmt| intravisit::walk_stmt(&mut walker, stmt));
if let Some(expr) = block.expr {
intravisit::walk_expr(&mut walker, expr);
}
walker.result
})
})
}
fn emit_branches_sharing_code_lint(
cx: &LateContext<'tcx>,
start_stmts: usize,
end_stmts: usize,
lint_end: bool,
warn_about_moved_symbol: bool,
blocks: &[&Block<'tcx>],
if_expr: &'tcx Expr<'_>,
) {
if start_stmts == 0 && !lint_end {
return;
}
// (help, span, suggestion)
let mut suggestions: Vec<(&str, Span, String)> = vec![];
let mut add_expr_note = false;
// Construct suggestions
let sm = cx.sess().source_map();
if start_stmts > 0 {
let block = blocks[0];
let span_start = first_line_of_span(cx, if_expr.span).shrink_to_lo();
let span_end = sm.stmt_span(block.stmts[start_stmts - 1].span, block.span);
let cond_span = first_line_of_span(cx, if_expr.span).until(block.span);
let cond_snippet = reindent_multiline(snippet(cx, cond_span, "_"), false, None);
let cond_indent = indent_of(cx, cond_span);
let moved_span = block.stmts[0].span.source_callsite().to(span_end);
let moved_snippet = reindent_multiline(snippet(cx, moved_span, "_"), true, None);
let suggestion = moved_snippet.to_string() + "\n" + &cond_snippet + "{";
let suggestion = reindent_multiline(Cow::Borrowed(&suggestion), true, cond_indent);
let span = span_start.to(span_end);
suggestions.push(("start", span, suggestion.to_string()));
}
if lint_end {
let block = blocks[blocks.len() - 1];
let span_end = block.span.shrink_to_hi();
let moved_start = if end_stmts == 0 && block.expr.is_some() {
block.expr.unwrap().span.source_callsite()
} else {
sm.stmt_span(block.stmts[block.stmts.len() - end_stmts].span, block.span)
};
let moved_end = block
.expr
.map_or_else(
|| sm.stmt_span(block.stmts[block.stmts.len() - 1].span, block.span),
|expr| expr.span.source_callsite(),
);
let moved_span = moved_start.to(moved_end);
let moved_snipped = reindent_multiline(snippet(cx, moved_span, "_"), true, None);
let indent = indent_of(cx, if_expr.span.shrink_to_hi());
let suggestion = "}\n".to_string() + &moved_snipped;
let suggestion = reindent_multiline(Cow::Borrowed(&suggestion), true, indent);
let mut span = moved_start.to(span_end);
// Improve formatting if the inner block has indention (i.e. normal Rust formatting)
let test_span = Span::new(span.lo() - BytePos(4), span.lo(), span.ctxt(), span.parent());
if snippet_opt(cx, test_span)
.map(|snip| snip == " ")
.unwrap_or_default()
{
span = span.with_lo(test_span.lo());
}
suggestions.push(("end", span, suggestion.to_string()));
add_expr_note = !cx.typeck_results().expr_ty(if_expr).is_unit();
}
let add_optional_msgs = |diag: &mut DiagnosticBuilder<'_>| {
if add_expr_note {
diag.note("The end suggestion probably needs some adjustments to use the expression result correctly");
}
if warn_about_moved_symbol {
diag.warn("Some moved values might need to be renamed to avoid wrong references");
}
};
// Emit lint
if suggestions.len() == 1 {
let (place_str, span, sugg) = suggestions.pop().unwrap();
let msg = format!("all if blocks contain the same code at the {}", place_str);
let help = format!("consider moving the {} statements out like this", place_str);
span_lint_and_then(cx, BRANCHES_SHARING_CODE, span, msg.as_str(), |diag| {
diag.span_suggestion(span, help.as_str(), sugg, Applicability::Unspecified);
add_optional_msgs(diag);
});
} else if suggestions.len() == 2 {
let (_, end_span, end_sugg) = suggestions.pop().unwrap();
let (_, start_span, start_sugg) = suggestions.pop().unwrap();
span_lint_and_then(
cx,
BRANCHES_SHARING_CODE,
start_span,
"all if blocks contain the same code at the start and the end. Here at the start",
move |diag| {
diag.span_note(end_span, "and here at the end");
diag.span_suggestion(
start_span,
"consider moving the start statements out like this",
start_sugg,
Applicability::Unspecified,
);
diag.span_suggestion(
end_span,
"and consider moving the end statements out like this",
end_sugg,
Applicability::Unspecified,
);
add_optional_msgs(diag);
},
);
}
}
/// This visitor collects `HirId`s and Symbols of defined symbols and `HirId`s of used values.
struct UsedValueFinderVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
/// The `HirId`s of defined values in the scanned statements
defs: FxHashSet<HirId>,
/// The Symbols of the defined symbols in the scanned statements
def_symbols: FxHashSet<Symbol>,
/// The `HirId`s of the used values
uses: FxHashSet<HirId>,
}
impl<'a, 'tcx> UsedValueFinderVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>) -> Self {
UsedValueFinderVisitor {
cx,
defs: FxHashSet::default(),
def_symbols: FxHashSet::default(),
uses: FxHashSet::default(),
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for UsedValueFinderVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::All(self.cx.tcx.hir())
}
fn visit_local(&mut self, l: &'tcx rustc_hir::Local<'tcx>) {
let local_id = l.pat.hir_id;
self.defs.insert(local_id);
if let Some(sym) = l.pat.simple_ident() {
self.def_symbols.insert(sym.name);
}
if let Some(expr) = l.init {
intravisit::walk_expr(self, expr);
}
}
fn visit_qpath(&mut self, qpath: &'tcx rustc_hir::QPath<'tcx>, id: HirId, _span: rustc_span::Span) {
if let rustc_hir::QPath::Resolved(_, path) = *qpath {
if path.segments.len() == 1 {
if let rustc_hir::def::Res::Local(var) = self.cx.qpath_res(qpath, id) {
self.uses.insert(var);
}
}
}
}
}
/// Implementation of `IFS_SAME_COND`.
fn lint_same_cond(cx: &LateContext<'_>, conds: &[&Expr<'_>]) {
let hash: &dyn Fn(&&Expr<'_>) -> u64 = &|expr| -> u64 {
let mut h = SpanlessHash::new(cx);
h.hash_expr(expr);
h.finish()
};
let eq: &dyn Fn(&&Expr<'_>, &&Expr<'_>) -> bool = &|&lhs, &rhs| -> bool { eq_expr_value(cx, lhs, rhs) };
for (i, j) in search_same(conds, hash, eq) {
span_lint_and_note(
cx,
IFS_SAME_COND,
j.span,
"this `if` has the same condition as a previous `if`",
Some(i.span),
"same as this",
);
}
}
/// Implementation of `SAME_FUNCTIONS_IN_IF_CONDITION`.
fn lint_same_fns_in_if_cond(cx: &LateContext<'_>, conds: &[&Expr<'_>]) {
let hash: &dyn Fn(&&Expr<'_>) -> u64 = &|expr| -> u64 {
let mut h = SpanlessHash::new(cx);
h.hash_expr(expr);
h.finish()
};
let eq: &dyn Fn(&&Expr<'_>, &&Expr<'_>) -> bool = &|&lhs, &rhs| -> bool {
// Do not lint if any expr originates from a macro
if in_macro(lhs.span) || in_macro(rhs.span) {
return false;
}
// Do not spawn warning if `IFS_SAME_COND` already produced it.
if eq_expr_value(cx, lhs, rhs) {
return false;
}
SpanlessEq::new(cx).eq_expr(lhs, rhs)
};
for (i, j) in search_same(conds, hash, eq) {
span_lint_and_note(
cx,
SAME_FUNCTIONS_IN_IF_CONDITION,
j.span,
"this `if` has the same function call as a previous `if`",
Some(i.span),
"same as this",
);
}
}