rust-clippy/clippy_lints/src/explicit_write.rs

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use rustc::hir::*;
use rustc::lint::*;
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use rustc::{declare_lint, lint_array};
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use crate::utils::{is_expn_of, match_def_path, resolve_node, span_lint};
use crate::utils::opt_def_id;
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/// **What it does:** Checks for usage of `write!()` / `writeln()!` which can be
/// replaced with `(e)print!()` / `(e)println!()`
///
/// **Why is this bad?** Using `(e)println! is clearer and more concise
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// // this would be clearer as `eprintln!("foo: {:?}", bar);`
/// writeln!(&mut io::stderr(), "foo: {:?}", bar).unwrap();
/// ```
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declare_clippy_lint! {
pub EXPLICIT_WRITE,
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complexity,
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"using the `write!()` family of functions instead of the `print!()` family \
of functions, when using the latter would work"
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}
#[derive(Copy, Clone, Debug)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(EXPLICIT_WRITE)
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}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if_chain! {
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// match call to unwrap
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if let ExprKind::MethodCall(ref unwrap_fun, _, ref unwrap_args) = expr.node;
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if unwrap_fun.ident.name == "unwrap";
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// match call to write_fmt
if unwrap_args.len() > 0;
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if let ExprKind::MethodCall(ref write_fun, _, ref write_args) =
unwrap_args[0].node;
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if write_fun.ident.name == "write_fmt";
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// match calls to std::io::stdout() / std::io::stderr ()
if write_args.len() > 0;
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if let ExprKind::Call(ref dest_fun, _) = write_args[0].node;
if let ExprKind::Path(ref qpath) = dest_fun.node;
if let Some(dest_fun_id) =
opt_def_id(resolve_node(cx, qpath, dest_fun.hir_id));
if let Some(dest_name) = if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stdout"]) {
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Some("stdout")
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} else if match_def_path(cx.tcx, dest_fun_id, &["std", "io", "stdio", "stderr"]) {
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Some("stderr")
} else {
None
};
then {
let write_span = unwrap_args[0].span;
let calling_macro =
// ordering is important here, since `writeln!` uses `write!` internally
if is_expn_of(write_span, "writeln").is_some() {
Some("writeln")
} else if is_expn_of(write_span, "write").is_some() {
Some("write")
} else {
None
};
let prefix = if dest_name == "stderr" {
"e"
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} else {
""
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};
if let Some(macro_name) = calling_macro {
span_lint(
cx,
EXPLICIT_WRITE,
expr.span,
&format!(
"use of `{}!({}(), ...).unwrap()`. Consider using `{}{}!` instead",
macro_name,
dest_name,
prefix,
macro_name.replace("write", "print")
)
);
} else {
span_lint(
cx,
EXPLICIT_WRITE,
expr.span,
&format!(
"use of `{}().write_fmt(...).unwrap()`. Consider using `{}print!` instead",
dest_name,
prefix,
)
);
}
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}
}
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}
}