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Merge pull request #566 from mcarton/starts_with

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Add a lint for starts_with
This commit is contained in:
llogiq 2016-01-20 20:15:10 +01:00
commit c570fc6079
5 changed files with 113 additions and 32 deletions
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3
README.md
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@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
[Jump to usage instructions](#usage)
##Lints
There are 94 lints included in this crate:
There are 95 lints included in this crate:
name | default | meaning
---------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@ -20,6 +20,7 @@ name
[cast_possible_wrap](https://github.com/Manishearth/rust-clippy/wiki#cast_possible_wrap) | allow | casts that may cause wrapping around the value, e.g `x as i32` where `x: u32` and `x > i32::MAX`
[cast_precision_loss](https://github.com/Manishearth/rust-clippy/wiki#cast_precision_loss) | allow | casts that cause loss of precision, e.g `x as f32` where `x: u64`
[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`
[chars_next_cmp](https://github.com/Manishearth/rust-clippy/wiki#chars_next_cmp) | warn | using `.chars().next()` to check if a string starts with a char
[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() }`

1
src/lib.rs
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@ -191,6 +191,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
matches::MATCH_OVERLAPPING_ARM,
matches::MATCH_REF_PATS,
matches::SINGLE_MATCH,
methods::CHARS_NEXT_CMP,
methods::FILTER_NEXT,
methods::OK_EXPECT,
methods::OPTION_MAP_UNWRAP_OR,

120
src/methods.rs
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@ -7,11 +7,14 @@ use std::borrow::Cow;
use syntax::ptr::P;
use syntax::codemap::Span;
use utils::{snippet, span_lint, span_note_and_lint, match_path, match_type, method_chain_args, match_trait_method,
walk_ptrs_ty_depth, walk_ptrs_ty, get_trait_def_id, implements_trait};
use utils::{
BTREEMAP_ENTRY_PATH, DEFAULT_TRAIT_PATH, HASHMAP_ENTRY_PATH, OPTION_PATH,
RESULT_PATH, STRING_PATH
get_trait_def_id, implements_trait, in_external_macro, in_macro, match_path,
match_trait_method, match_type, method_chain_args, snippet, span_lint, span_lint_and_then,
span_note_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth,
};
use utils::{
BTREEMAP_ENTRY_PATH, DEFAULT_TRAIT_PATH, HASHMAP_ENTRY_PATH, OPTION_PATH, RESULT_PATH,
STRING_PATH
};
use utils::MethodArgs;
use rustc::middle::cstore::CrateStore;
@ -176,6 +179,17 @@ declare_lint!(pub SEARCH_IS_SOME, Warn,
"using an iterator search followed by `is_some()`, which is more succinctly \
expressed as a call to `any()`");
/// **What it does:** This lint `Warn`s on using `.chars().next()` on a `str` to check if it
/// starts with a given char.
///
/// **Why is this bad?** Readability, this can be written more concisely as `_.starts_with(_)`.
///
/// **Known problems:** None.
///
/// **Example:** `name.chars().next() == Some('_')`
declare_lint!(pub CHARS_NEXT_CMP, Warn,
"using `.chars().next()` to check if a string starts with a char");
/// **What it does:** This lint checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`, etc., and
/// suggests to use `or_else`, `unwrap_or_else`, etc., or `unwrap_or_default` instead.
///
@ -210,39 +224,56 @@ impl LintPass for MethodsPass {
OK_EXPECT,
OPTION_MAP_UNWRAP_OR,
OPTION_MAP_UNWRAP_OR_ELSE,
OR_FUN_CALL)
OR_FUN_CALL,
CHARS_NEXT_CMP)
}
}
impl LateLintPass for MethodsPass {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let ExprMethodCall(name, _, ref args) = expr.node {
// Chain calls
if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
lint_unwrap(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["to_string"]) {
lint_to_string(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["ok", "expect"]) {
lint_ok_expect(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or"]) {
lint_map_unwrap_or(cx, expr, arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or_else"]) {
lint_map_unwrap_or_else(cx, expr, arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["filter", "next"]) {
lint_filter_next(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["find", "is_some"]) {
lint_search_is_some(cx, expr, "find", arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["position", "is_some"]) {
lint_search_is_some(cx, expr, "position", arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["rposition", "is_some"]) {
lint_search_is_some(cx, expr, "rposition", arglists[0], arglists[1]);
}
if in_macro(cx, expr.span) {
return;
}
lint_or_fun_call(cx, expr, &name.node.as_str(), &args);
match expr.node {
ExprMethodCall(name, _, ref args) => {
// Chain calls
if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
lint_unwrap(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["to_string"]) {
lint_to_string(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["ok", "expect"]) {
lint_ok_expect(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or"]) {
lint_map_unwrap_or(cx, expr, arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or_else"]) {
lint_map_unwrap_or_else(cx, expr, arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["filter", "next"]) {
lint_filter_next(cx, expr, arglists[0]);
} else if let Some(arglists) = method_chain_args(expr, &["find", "is_some"]) {
lint_search_is_some(cx, expr, "find", arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["position", "is_some"]) {
lint_search_is_some(cx, expr, "position", arglists[0], arglists[1]);
} else if let Some(arglists) = method_chain_args(expr, &["rposition", "is_some"]) {
lint_search_is_some(cx, expr, "rposition", arglists[0], arglists[1]);
}
lint_or_fun_call(cx, expr, &name.node.as_str(), &args);
}
ExprBinary(op, ref lhs, ref rhs) if op.node == BiEq || op.node == BiNe => {
if !lint_chars_next(cx, expr, lhs, rhs, op.node == BiEq) {
lint_chars_next(cx, expr, rhs, lhs, op.node == BiEq);
}
}
_ => (),
}
}
fn check_item(&mut self, cx: &LateContext, item: &Item) {
if in_external_macro(cx, item.span) {
return;
}
if let ItemImpl(_, _, _, None, ref ty, ref items) = item.node {
for implitem in items {
let name = implitem.name;
@ -570,6 +601,41 @@ fn lint_search_is_some(cx: &LateContext, expr: &Expr, search_method: &str, searc
}
}
/// Checks for the `CHARS_NEXT_CMP` lint.
fn lint_chars_next(cx: &LateContext, expr: &Expr, chain: &Expr, other: &Expr, eq: bool) -> bool {
if_let_chain! {[
let Some(args) = method_chain_args(chain, &["chars", "next"]),
let ExprCall(ref fun, ref arg_char) = other.node,
arg_char.len() == 1,
let ExprPath(None, ref path) = fun.node,
path.segments.len() == 1 && path.segments[0].identifier.name.as_str() == "Some"
], {
let self_ty = walk_ptrs_ty(cx.tcx.expr_ty_adjusted(&args[0][0]));
if self_ty.sty != ty::TyStr {
return false;
}
span_lint_and_then(cx,
CHARS_NEXT_CMP,
expr.span,
"you should use the `starts_with` method",
|db| {
let sugg = format!("{}{}.starts_with({})",
if eq { "" } else { "!" },
snippet(cx, args[0][0].span, "_"),
snippet(cx, arg_char[0].span, "_")
);
db.span_suggestion(expr.span, "like this", sugg);
});
return true;
}}
false
}
// Given a `Result<T, E>` type, return its error type (`E`)
fn get_error_type<'a>(cx: &LateContext, ty: ty::Ty<'a>) -> Option<ty::Ty<'a>> {
if !match_type(cx, ty, &RESULT_PATH) {

9
src/misc.rs
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@ -389,13 +389,14 @@ impl LateLintPass for UsedUnderscoreBinding {
.last()
.expect("path should always have at least one segment")
.identifier;
ident.name.as_str().chars().next() == Some('_') && // starts with '_'
ident.name.as_str().chars().skip(1).next() != Some('_') && // doesn't start with "__"
ident.name != ident.unhygienic_name && is_used(cx, expr) // not in bang macro
ident.name.as_str().starts_with('_') &&
!ident.name.as_str().starts_with("__") &&
ident.name != ident.unhygienic_name &&
is_used(cx, expr) // not in bang macro
}
ExprField(_, spanned) => {
let name = spanned.node.as_str();
name.chars().next() == Some('_') && name.chars().skip(1).next() != Some('_')
name.starts_with('_') && !name.starts_with("__")
}
_ => false,
};

12
tests/compile-fail/methods.rs
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@ -292,3 +292,15 @@ struct MyError(()); // doesn't implement Debug
struct MyErrorWithParam<T> {
x: T
}
fn starts_with() {
"".chars().next() == Some(' ');
//~^ ERROR starts_with
//~| HELP like this
//~| SUGGESTION "".starts_with(' ')
Some(' ') != "".chars().next();
//~^ ERROR starts_with
//~| HELP like this
//~| SUGGESTION !"".starts_with(' ')
}