Fix `read_zero_byte_vec` suggests wrongly inside `let` stmt (#15582)

Closes rust-lang/rust-clippy#15575

changelog: [`read_zero_byte_vec`] fix wrong suggestions inside `let`
stmt

3 files changed, 109 insertions, 10 deletions

diff --git a/clippy_lints/src/read_zero_byte_vec.rs b/clippy_lints/src/read_zero_byte_vec.rs
index acd840401c6..b8d4e7c4651 100644
--- a/clippy_lints/src/read_zero_byte_vec.rs
+++ b/clippy_lints/src/read_zero_byte_vec.rs
@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then};
 use clippy_utils::higher::{VecInitKind, get_vec_init_kind};
-use clippy_utils::source::snippet;
+use clippy_utils::source::{indent_of, snippet};
 use clippy_utils::{get_enclosing_block, sym};
 
 use rustc_errors::Applicability;
@@ -83,10 +83,12 @@ impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec {
                             expr.span,
                             "reading zero byte data to `Vec`",
                             |diag| {
+                                let span = first_stmt_containing_expr(cx, expr).map_or(expr.span, |stmt| stmt.span);
+                                let indent = indent_of(cx, span).unwrap_or(0);
                                 diag.span_suggestion(
-                                    expr.span,
+                                    span.shrink_to_lo(),
                                     "try",
-                                    format!("{}.resize({len}, 0); {}", ident, snippet(cx, expr.span, "..")),
+                                    format!("{ident}.resize({len}, 0);\n{}", " ".repeat(indent)),
                                     applicability,
                                 );
                             },
@@ -100,14 +102,15 @@ impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec {
                                 expr.span,
                                 "reading zero byte data to `Vec`",
                                 |diag| {
+                                    let span = first_stmt_containing_expr(cx, expr).map_or(expr.span, |stmt| stmt.span);
+                                    let indent = indent_of(cx, span).unwrap_or(0);
                                     diag.span_suggestion(
-                                        expr.span,
+                                        span.shrink_to_lo(),
                                         "try",
                                         format!(
-                                            "{}.resize({}, 0); {}",
-                                            ident,
+                                            "{ident}.resize({}, 0);\n{}",
                                             snippet(cx, e.span, ".."),
-                                            snippet(cx, expr.span, "..")
+                                            " ".repeat(indent)
                                         ),
                                         applicability,
                                     );
@@ -130,6 +133,16 @@ impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec {
     }
 }
 
+fn first_stmt_containing_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Option<&'tcx hir::Stmt<'tcx>> {
+    cx.tcx.hir_parent_iter(expr.hir_id).find_map(|(_, node)| {
+        if let hir::Node::Stmt(stmt) = node {
+            Some(stmt)
+        } else {
+            None
+        }
+    })
+}
+
 struct ReadVecVisitor<'tcx> {
     local_id: HirId,
     read_zero_expr: Option<&'tcx Expr<'tcx>>,
diff --git a/tests/ui/read_zero_byte_vec.rs b/tests/ui/read_zero_byte_vec.rs
index 938d61b6860..720276cb554 100644
--- a/tests/ui/read_zero_byte_vec.rs
+++ b/tests/ui/read_zero_byte_vec.rs
@@ -120,3 +120,30 @@ fn allow_works<F: std::io::Read>(mut f: F) {
 }
 
 fn main() {}
+
+fn issue15575() -> usize {
+    use std::io::Read;
+    use std::net::TcpListener;
+
+    let listener = TcpListener::bind("127.0.0.1:9010").unwrap();
+    let mut stream_and_addr = listener.accept().unwrap();
+    let mut buf = Vec::with_capacity(32);
+    let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+    //~^ read_zero_byte_vec
+
+    let cap = 1000;
+    let mut buf = Vec::with_capacity(cap);
+    let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+    //~^ read_zero_byte_vec
+
+    let cap = 1000;
+    let mut buf = Vec::with_capacity(cap);
+    let num_bytes_received = { stream_and_addr.0.read(&mut buf) }.unwrap();
+    //~^ read_zero_byte_vec
+
+    use std::fs::File;
+    let mut f = File::open("foo.txt").unwrap();
+    let mut data = Vec::with_capacity(100);
+    f.read(&mut data).unwrap()
+    //~^ read_zero_byte_vec
+}
diff --git a/tests/ui/read_zero_byte_vec.stderr b/tests/ui/read_zero_byte_vec.stderr
index 8f255bc87ab..8dd74592e4c 100644
--- a/tests/ui/read_zero_byte_vec.stderr
+++ b/tests/ui/read_zero_byte_vec.stderr
@@ -2,16 +2,27 @@ error: reading zero byte data to `Vec`
   --> tests/ui/read_zero_byte_vec.rs:22:5
    |
 LL |     f.read_exact(&mut data).unwrap();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `data.resize(20, 0); f.read_exact(&mut data)`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::read-zero-byte-vec` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::read_zero_byte_vec)]`
+help: try
+   |
+LL ~     data.resize(20, 0);
+LL ~     f.read_exact(&mut data).unwrap();
+   |
 
 error: reading zero byte data to `Vec`
   --> tests/ui/read_zero_byte_vec.rs:28:5
    |
 LL |     f.read_exact(&mut data2)?;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `data2.resize(cap, 0); f.read_exact(&mut data2)`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~     data2.resize(cap, 0);
+LL ~     f.read_exact(&mut data2)?;
+   |
 
 error: reading zero byte data to `Vec`
   --> tests/ui/read_zero_byte_vec.rs:33:5
@@ -67,5 +78,53 @@ error: reading zero byte data to `Vec`
 LL |     r.read_exact(&mut data2).await.unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 11 previous errors
+error: reading zero byte data to `Vec`
+  --> tests/ui/read_zero_byte_vec.rs:131:30
+   |
+LL |     let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~     buf.resize(32, 0);
+LL ~     let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+   |
+
+error: reading zero byte data to `Vec`
+  --> tests/ui/read_zero_byte_vec.rs:136:30
+   |
+LL |     let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~     buf.resize(cap, 0);
+LL ~     let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
+   |
+
+error: reading zero byte data to `Vec`
+  --> tests/ui/read_zero_byte_vec.rs:141:32
+   |
+LL |     let num_bytes_received = { stream_and_addr.0.read(&mut buf) }.unwrap();
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~     buf.resize(cap, 0);
+LL ~     let num_bytes_received = { stream_and_addr.0.read(&mut buf) }.unwrap();
+   |
+
+error: reading zero byte data to `Vec`
+  --> tests/ui/read_zero_byte_vec.rs:147:5
+   |
+LL |     f.read(&mut data).unwrap()
+   |     ^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL ~     data.resize(100, 0);
+LL ~     f.read(&mut data).unwrap()
+   |
+
+error: aborting due to 15 previous errors