Merge commit 'd7b5cbf065b88830ca519adcb73fad4c0d24b1c7' into clippyup

1 files changed, 142 insertions, 0 deletions

diff --git a/clippy_lints/src/read_zero_byte_vec.rs b/clippy_lints/src/read_zero_byte_vec.rs
new file mode 100644
index 00000000000..9538a810473
--- /dev/null
+++ b/clippy_lints/src/read_zero_byte_vec.rs
@@ -0,0 +1,142 @@
+use clippy_utils::{
+    diagnostics::{span_lint, span_lint_and_sugg},
+    higher::{get_vec_init_kind, VecInitKind},
+    source::snippet,
+    visitors::expr_visitor_no_bodies,
+};
+use hir::{intravisit::Visitor, ExprKind, Local, PatKind, PathSegment, QPath, StmtKind};
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// This lint catches reads into a zero-length `Vec`.
+    /// Especially in the case of a call to `with_capacity`, this lint warns that read
+    /// gets the number of bytes from the `Vec`'s length, not its capacity.
+    ///
+    /// ### Why is this bad?
+    /// Reading zero bytes is almost certainly not the intended behavior.
+    ///
+    /// ### Known problems
+    /// In theory, a very unusual read implementation could assign some semantic meaning
+    /// to zero-byte reads. But it seems exceptionally unlikely that code intending to do
+    /// a zero-byte read would allocate a `Vec` for it.
+    ///
+    /// ### Example
+    /// ```rust
+    /// use std::io;
+    /// fn foo<F: io::Read>(mut f: F) {
+    ///     let mut data = Vec::with_capacity(100);
+    ///     f.read(&mut data).unwrap();
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// use std::io;
+    /// fn foo<F: io::Read>(mut f: F) {
+    ///     let mut data = Vec::with_capacity(100);
+    ///     data.resize(100, 0);
+    ///     f.read(&mut data).unwrap();
+    /// }
+    /// ```
+    #[clippy::version = "1.63.0"]
+    pub READ_ZERO_BYTE_VEC,
+    correctness,
+    "checks for reads into a zero-length `Vec`"
+}
+declare_lint_pass!(ReadZeroByteVec => [READ_ZERO_BYTE_VEC]);
+
+impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec {
+    fn check_block(&mut self, cx: &LateContext<'tcx>, block: &hir::Block<'tcx>) {
+        for (idx, stmt) in block.stmts.iter().enumerate() {
+            if !stmt.span.from_expansion()
+                // matches `let v = Vec::new();`
+                && let StmtKind::Local(local) = stmt.kind
+                && let Local { pat, init: Some(init), .. } = local
+                && let PatKind::Binding(_, _, ident, _) = pat.kind
+                && let Some(vec_init_kind) = get_vec_init_kind(cx, init)
+            {
+                // finds use of `_.read(&mut v)`
+                let mut read_found = false;
+                let mut visitor = expr_visitor_no_bodies(|expr| {
+                    if let ExprKind::MethodCall(path, [_self, arg], _) = expr.kind
+                        && let PathSegment { ident: read_or_read_exact, .. } = *path
+                        && matches!(read_or_read_exact.as_str(), "read" | "read_exact")
+                        && let ExprKind::AddrOf(_, hir::Mutability::Mut, inner) = arg.kind
+                        && let ExprKind::Path(QPath::Resolved(None, inner_path)) = inner.kind
+                        && let [inner_seg] = inner_path.segments
+                        && ident.name == inner_seg.ident.name
+                    {
+                        read_found = true;
+                    }
+                    !read_found
+                });
+
+                let next_stmt_span;
+                if idx == block.stmts.len() - 1 {
+                    // case { .. stmt; expr }
+                    if let Some(e) = block.expr {
+                        visitor.visit_expr(e);
+                        next_stmt_span = e.span;
+                    } else {
+                        return;
+                    }
+                } else {
+                    // case { .. stmt; stmt; .. }
+                    let next_stmt = &block.stmts[idx + 1];
+                    visitor.visit_stmt(next_stmt);
+                    next_stmt_span = next_stmt.span;
+                }
+                drop(visitor);
+
+                if read_found && !next_stmt_span.from_expansion() {
+                    let applicability = Applicability::MaybeIncorrect;
+                    match vec_init_kind {
+                        VecInitKind::WithConstCapacity(len) => {
+                            span_lint_and_sugg(
+                                cx,
+                                READ_ZERO_BYTE_VEC,
+                                next_stmt_span,
+                                "reading zero byte data to `Vec`",
+                                "try",
+                                format!("{}.resize({}, 0); {}",
+                                    ident.as_str(),
+                                    len,
+                                    snippet(cx, next_stmt_span, "..")
+                                ),
+                                applicability,
+                            );
+                        }
+                        VecInitKind::WithExprCapacity(hir_id) => {
+                            let e = cx.tcx.hir().expect_expr(hir_id);
+                            span_lint_and_sugg(
+                                cx,
+                                READ_ZERO_BYTE_VEC,
+                                next_stmt_span,
+                                "reading zero byte data to `Vec`",
+                                "try",
+                                format!("{}.resize({}, 0); {}",
+                                    ident.as_str(),
+                                    snippet(cx, e.span, ".."),
+                                    snippet(cx, next_stmt_span, "..")
+                                ),
+                                applicability,
+                            );
+                        }
+                        _ => {
+                            span_lint(
+                                cx,
+                                READ_ZERO_BYTE_VEC,
+                                next_stmt_span,
+                                "reading zero byte data to `Vec`",
+                            );
+
+                        }
+                    }
+                }
+            }
+        }
+    }
+}