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Lint about else { if .. } with useless braces

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This commit is contained in:
mcarton 2016-01-13 18:32:55 +01:00
parent 375b8168e4
commit c2444c6043
3 changed files with 73 additions and 24 deletions
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2
README.md
View File

@ -22,7 +22,7 @@ name
[cast_sign_loss](https://github.com/Manishearth/rust-clippy/wiki#cast_sign_loss) | allow | casts from signed types to unsigned types, e.g `x as u32` where `x: i32`
[cmp_nan](https://github.com/Manishearth/rust-clippy/wiki#cmp_nan) | deny | comparisons to NAN (which will always return false, which is probably not intended)
[cmp_owned](https://github.com/Manishearth/rust-clippy/wiki#cmp_owned) | warn | creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
[collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#collapsible_if) | warn | two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }`
[collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#collapsible_if) | warn | two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }` and an `else { if .. } expression can be collapsed to `else if`
[cyclomatic_complexity](https://github.com/Manishearth/rust-clippy/wiki#cyclomatic_complexity) | warn | finds functions that should be split up into multiple functions
[deprecated_semver](https://github.com/Manishearth/rust-clippy/wiki#deprecated_semver) | warn | `Warn` on `#[deprecated(since = "x")]` where x is not semver
[duplicate_underscore_argument](https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument) | warn | Function arguments having names which only differ by an underscore

71
src/collapsible_if.rs
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@ -16,9 +16,11 @@ use rustc::lint::*;
use rustc_front::hir::*;
use syntax::codemap::Spanned;
use utils::{in_macro, span_help_and_lint, snippet, snippet_block};
use utils::{in_macro, snippet, snippet_block, span_lint_and_then};
/// **What it does:** This lint checks for nested `if`-statements which can be collapsed by `&&`-combining their conditions. It is `Warn` by default.
/// **What it does:** This lint checks for nested `if`-statements which can be collapsed by
/// `&&`-combining their conditions and for `else { if .. } expressions that can be collapsed to
/// `else if ..`. It is `Warn` by default.
///
/// **Why is this bad?** Each `if`-statement adds one level of nesting, which makes code look more complex than it really is.
///
@ -29,7 +31,8 @@ declare_lint! {
pub COLLAPSIBLE_IF,
Warn,
"two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` \
can be written as `if x && y { foo() }`"
can be written as `if x && y { foo() }` and an `else { if .. } expression can be collapsed to \
`else if`"
}
#[derive(Copy,Clone)]
@ -50,20 +53,44 @@ impl LateLintPass for CollapsibleIf {
}
fn check_if(cx: &LateContext, e: &Expr) {
if let ExprIf(ref check, ref then, None) = e.node {
if let Some(&Expr{ node: ExprIf(ref check_inner, ref content, None), span: sp, ..}) =
single_stmt_of_block(then) {
if e.span.expn_id != sp.expn_id {
return;
if let ExprIf(ref check, ref then, ref else_) = e.node {
match *else_ {
Some(ref else_) => {
if_let_chain! {[
let ExprBlock(ref block) = else_.node,
block.stmts.is_empty(),
block.rules == BlockCheckMode::DefaultBlock,
let Some(ref else_) = block.expr,
let ExprIf(_, _, _) = else_.node
], {
span_lint_and_then(cx,
COLLAPSIBLE_IF,
block.span,
"this `else { if .. }` block can be collapsed", |db| {
db.span_suggestion(block.span, "try",
format!("else {}",
snippet_block(cx, else_.span, "..")));
});
}}
}
None => {
if let Some(&Expr{ node: ExprIf(ref check_inner, ref content, None), span: sp, ..}) =
single_stmt_of_block(then) {
if e.span.expn_id != sp.expn_id {
return;
}
span_lint_and_then(cx,
COLLAPSIBLE_IF,
e.span,
"this if statement can be collapsed", |db| {
db.span_suggestion(e.span, "try",
format!("if {} && {} {}",
check_to_string(cx, check),
check_to_string(cx, check_inner),
snippet_block(cx, content.span, "..")));
});
}
}
span_help_and_lint(cx,
COLLAPSIBLE_IF,
e.span,
"this if statement can be collapsed",
&format!("try\nif {} && {} {}",
check_to_string(cx, check),
check_to_string(cx, check_inner),
snippet_block(cx, content.span, "..")));
}
}
}
@ -90,16 +117,14 @@ fn single_stmt_of_block(block: &Block) -> Option<&Expr> {
} else {
None
}
} else {
if block.stmts.is_empty() {
if let Some(ref p) = block.expr {
Some(p)
} else {
None
}
} else if block.stmts.is_empty() {
if let Some(ref p) = block.expr {
Some(p)
} else {
None
}
} else {
None
}
}

24
tests/compile-fail/collapsible_if.rs
View File

@ -17,6 +17,30 @@ fn main() {
}
}
// Collaspe `else { if .. }` to `else if ..`
if x == "hello" {
print!("Hello ");
} else { //~ERROR: this `else { if .. }`
//~| HELP try
//~| SUGGESTION else if y == "world"
if y == "world" {
println!("world!")
}
}
if x == "hello" {
print!("Hello ");
} else { //~ERROR this `else { if .. }`
//~| HELP try
//~| SUGGESTION else if y == "world"
if y == "world" {
println!("world")
}
else {
println!("!")
}
}
// Works because any if with an else statement cannot be collapsed.
if x == "hello" {
if y == "world" {