clippy_lints/src/methods/seek_from_current.rs

use rustc_ast::ast::{LitIntType, LitKind};
use rustc_data_structures::packed::Pu128;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::LateContext;

use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::implements_trait;
use clippy_utils::{is_enum_variant_ctor, sym};

use super::SEEK_FROM_CURRENT;

pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, recv: &'tcx Expr<'_>, arg: &'tcx Expr<'_>) {
    let ty = cx.typeck_results().expr_ty(recv);

    if let Some(def_id) = cx.tcx.get_diagnostic_item(sym::IoSeek)
        && implements_trait(cx, ty, def_id, &[])
        && arg_is_seek_from_current(cx, arg)
    {
        let mut applicability = Applicability::MachineApplicable;
        let snip = snippet_with_applicability(cx, recv.span, "..", &mut applicability);

        span_lint_and_sugg(
            cx,
            SEEK_FROM_CURRENT,
            expr.span,
            "using `SeekFrom::Current` to start from current position",
            "replace with",
            format!("{snip}.stream_position()"),
            applicability,
        );
    }
}

fn arg_is_seek_from_current<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
    if let ExprKind::Call(f, [arg]) = expr.kind
        && let ExprKind::Path(ref path) = f.kind
        && let Some(ctor_call_id) = cx.qpath_res(path, f.hir_id).opt_def_id()
        && is_enum_variant_ctor(cx, sym::SeekFrom, sym::Current, ctor_call_id)
        // check if argument of `SeekFrom::Current` is `0`
        && let ExprKind::Lit(lit) = arg.kind
        && let LitKind::Int(Pu128(0), LitIntType::Unsuffixed) = lit.node
    {
        return true;
    }

    false
}