rust-clippy/clippy_lints/src/wildcard_imports.rs

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use crate::utils::{in_macro, snippet, snippet_with_applicability, span_lint_and_sugg};
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use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{
def::{DefKind, Res},
Item, ItemKind, PathSegment, UseKind,
};
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use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::symbol::kw;
use rustc_span::{sym, BytePos};
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declare_clippy_lint! {
/// **What it does:** Checks for `use Enum::*`.
///
/// **Why is this bad?** It is usually better style to use the prefixed name of
/// an enumeration variant, rather than importing variants.
///
/// **Known problems:** Old-style enumerations that prefix the variants are
/// still around.
///
/// **Example:**
/// ```rust,ignore
/// // Bad
/// use std::cmp::Ordering::*;
/// foo(Less);
///
/// // Good
/// use std::cmp::Ordering;
/// foo(Ordering::Less)
/// ```
pub ENUM_GLOB_USE,
pedantic,
"use items that import all variants of an enum"
}
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declare_clippy_lint! {
/// **What it does:** Checks for wildcard imports `use _::*`.
///
/// **Why is this bad?** wildcard imports can pollute the namespace. This is especially bad if
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/// you try to import something through a wildcard, that already has been imported by name from
/// a different source:
///
/// ```rust,ignore
/// use crate1::foo; // Imports a function named foo
/// use crate2::*; // Has a function named foo
///
/// foo(); // Calls crate1::foo
/// ```
///
/// This can lead to confusing error messages at best and to unexpected behavior at worst.
///
/// **Exceptions:**
///
/// Wildcard imports are allowed from modules named `prelude`. Many crates (including the standard library)
/// provide modules named "prelude" specifically designed for wildcard import.
///
/// `use super::*` is allowed in test modules. This is defined as any module with "test" in the name.
///
/// These exceptions can be disabled using the `warn-on-all-wildcard-imports` configuration flag.
///
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/// **Known problems:** If macros are imported through the wildcard, this macro is not included
/// by the suggestion and has to be added by hand.
///
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/// Applying the suggestion when explicit imports of the things imported with a glob import
/// exist, may result in `unused_imports` warnings.
///
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/// **Example:**
///
/// ```rust,ignore
/// // Bad
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/// use crate1::*;
///
/// foo();
/// ```
///
/// ```rust,ignore
/// // Good
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/// use crate1::foo;
///
/// foo();
/// ```
pub WILDCARD_IMPORTS,
pedantic,
"lint `use _::*` statements"
}
#[derive(Default)]
pub struct WildcardImports {
warn_on_all: bool,
test_modules_deep: u32,
}
impl WildcardImports {
pub fn new(warn_on_all: bool) -> Self {
Self {
warn_on_all,
test_modules_deep: 0,
}
}
}
impl_lint_pass!(WildcardImports => [ENUM_GLOB_USE, WILDCARD_IMPORTS]);
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impl LateLintPass<'_> for WildcardImports {
fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
if is_test_module_or_function(item) {
self.test_modules_deep = self.test_modules_deep.saturating_add(1);
}
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if item.vis.node.is_pub() || item.vis.node.is_pub_restricted() {
return;
}
if_chain! {
if let ItemKind::Use(use_path, UseKind::Glob) = &item.kind;
if self.warn_on_all || !self.check_exceptions(item, use_path.segments);
let used_imports = cx.tcx.names_imported_by_glob_use(item.hir_id.owner);
if !used_imports.is_empty(); // Already handled by `unused_imports`
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then {
let mut applicability = Applicability::MachineApplicable;
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let import_source_snippet = snippet_with_applicability(cx, use_path.span, "..", &mut applicability);
let (span, braced_glob) = if import_source_snippet.is_empty() {
// This is a `_::{_, *}` import
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// In this case `use_path.span` is empty and ends directly in front of the `*`,
// so we need to extend it by one byte.
(
use_path.span.with_hi(use_path.span.hi() + BytePos(1)),
true,
)
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} else {
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// In this case, the `use_path.span` ends right before the `::*`, so we need to
// extend it up to the `*`. Since it is hard to find the `*` in weird
// formattings like `use _ :: *;`, we extend it up to, but not including the
// `;`. In nested imports, like `use _::{inner::*, _}` there is no `;` and we
// can just use the end of the item span
let mut span = use_path.span.with_hi(item.span.hi());
if snippet(cx, span, "").ends_with(';') {
span = use_path.span.with_hi(item.span.hi() - BytePos(1));
}
(
span, false,
)
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};
let imports_string = if used_imports.len() == 1 {
used_imports.iter().next().unwrap().to_string()
} else {
let mut imports = used_imports
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.iter()
.map(ToString::to_string)
.collect::<Vec<_>>();
imports.sort();
if braced_glob {
imports.join(", ")
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} else {
format!("{{{}}}", imports.join(", "))
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}
};
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let sugg = if braced_glob {
imports_string
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} else {
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format!("{}::{}", import_source_snippet, imports_string)
};
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let (lint, message) = if let Res::Def(DefKind::Enum, _) = use_path.res {
(ENUM_GLOB_USE, "usage of wildcard import for enum variants")
} else {
(WILDCARD_IMPORTS, "usage of wildcard import")
};
span_lint_and_sugg(
cx,
lint,
span,
message,
"try",
sugg,
applicability,
);
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}
}
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}
fn check_item_post(&mut self, _: &LateContext<'_>, item: &Item<'_>) {
if is_test_module_or_function(item) {
self.test_modules_deep = self.test_modules_deep.saturating_sub(1);
}
}
}
impl WildcardImports {
fn check_exceptions(&self, item: &Item<'_>, segments: &[PathSegment<'_>]) -> bool {
in_macro(item.span)
|| is_prelude_import(segments)
|| (is_super_only_import(segments) && self.test_modules_deep > 0)
}
}
// Allow "...prelude::..::*" imports.
// Many crates have a prelude, and it is imported as a glob by design.
fn is_prelude_import(segments: &[PathSegment<'_>]) -> bool {
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segments.iter().any(|ps| ps.ident.name == sym::prelude)
}
// Allow "super::*" imports in tests.
fn is_super_only_import(segments: &[PathSegment<'_>]) -> bool {
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segments.len() == 1 && segments[0].ident.name == kw::Super
}
fn is_test_module_or_function(item: &Item<'_>) -> bool {
matches!(item.kind, ItemKind::Mod(..)) && item.ident.name.as_str().contains("test")
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}