rust/clippy_lints/src/unused_io_amount.rs
2019-05-17 23:53:54 +02:00

87 lines
3.0 KiB
Rust

use crate::utils::{is_try, match_qpath, match_trait_method, paths, span_lint};
use rustc::hir;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for unused written/read amount.
///
/// **Why is this bad?** `io::Write::write` and `io::Read::read` are not
/// guaranteed to
/// process the entire buffer. They return how many bytes were processed, which
/// might be smaller
/// than a given buffer's length. If you don't need to deal with
/// partial-write/read, use
/// `write_all`/`read_exact` instead.
///
/// **Known problems:** Detects only common patterns.
///
/// **Example:**
/// ```rust,ignore
/// use std::io;
/// fn foo<W: io::Write>(w: &mut W) -> io::Result<()> {
/// // must be `w.write_all(b"foo")?;`
/// w.write(b"foo")?;
/// Ok(())
/// }
/// ```
pub UNUSED_IO_AMOUNT,
correctness,
"unused written/read amount"
}
declare_lint_pass!(UnusedIoAmount => [UNUSED_IO_AMOUNT]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedIoAmount {
fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
let expr = match s.node {
hir::StmtKind::Semi(ref expr) | hir::StmtKind::Expr(ref expr) => &**expr,
_ => return,
};
match expr.node {
hir::ExprKind::Match(ref res, _, _) if is_try(expr).is_some() => {
if let hir::ExprKind::Call(ref func, ref args) = res.node {
if let hir::ExprKind::Path(ref path) = func.node {
if match_qpath(path, &paths::TRY_INTO_RESULT) && args.len() == 1 {
check_method_call(cx, &args[0], expr);
}
}
} else {
check_method_call(cx, res, expr);
}
},
hir::ExprKind::MethodCall(ref path, _, ref args) => match &*path.ident.as_str() {
"expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
check_method_call(cx, &args[0], expr);
},
_ => (),
},
_ => (),
}
}
}
fn check_method_call(cx: &LateContext<'_, '_>, call: &hir::Expr, expr: &hir::Expr) {
if let hir::ExprKind::MethodCall(ref path, _, _) = call.node {
let symbol = &*path.ident.as_str();
if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
span_lint(
cx,
UNUSED_IO_AMOUNT,
expr.span,
"handle read amount returned or use `Read::read_exact` instead",
);
} else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
span_lint(
cx,
UNUSED_IO_AMOUNT,
expr.span,
"handle written amount returned or use `Write::write_all` instead",
);
}
}
}