added range to extend check

clippy_lints/src/append_instead_of_extend.rs

@@ -1,27 +1,27 @@
-use rustc_session::{declare_lint_pass, declare_tool_lint};
-// use rustc_ast::ast::*;
 use clippy_utils::diagnostics::span_lint_and_help;
-use clippy_utils::ty::is_type_diagnostic_item;
-use if_chain::if_chain;
-use rustc_hir::{Expr, ExprKind};
+use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item};
+use rustc_hir::{Expr, ExprKind, LangItem};
 use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::sym;
 
 declare_clippy_lint! {
-    /// **What it does:**
+    /// **What it does:** finds occurrences of `vec.extend(other_vec.drain(..))
     ///
-    /// **Why is this bad?**
+    /// **Why is this bad?** Slightly more succinct code and faster code
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     ///
     /// ```rust
     /// // example code where clippy issues a warning
+    /// vec![].extend(vec![1, 2, 3].drain(..))
     /// ```
     /// Use instead:
     /// ```rust
     /// // example code which does not raise clippy warning
+    /// vec![].append(&mut vec![])
     /// ```
     pub APPEND_INSTEAD_OF_EXTEND,
     perf,
@@ -32,30 +32,38 @@ declare_lint_pass!(AppendInsteadOfExtend => [APPEND_INSTEAD_OF_EXTEND]);
 
 impl<'tcx> LateLintPass<'tcx> for AppendInsteadOfExtend {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if is_vec_an_append(cx, expr) {
-            span_lint_and_help(
-                cx,
-                APPEND_INSTEAD_OF_EXTEND,
-                expr.span,
-                "use of `vec.extend(other_vec.drain(..))`",
-                None,
-                "consider using `vec![].append(&mut vec![]);` instead",
-            );
-        }
-    }
-}
+        //validate target object
+        if let ExprKind::MethodCall(method_name, _, exprs, _) = expr.kind {
+            //check source object
+            if let ExprKind::MethodCall(src_method, _, src_args, _) = &exprs[1].kind {
+                //check drain range
+                let ty = cx.typeck_results().expr_ty(&src_args[1]);
+                let ty = ty.peel_refs();
+                let range_check = is_type_lang_item(cx, ty, LangItem::RangeFull);
+
+                //check types
+                let ty = cx.typeck_results().expr_ty(&exprs[0]).peel_refs();
+                let vector_1 = is_type_diagnostic_item(cx, ty, sym::vec_type);
+
+                let src_ty = cx.typeck_results().expr_ty(&src_args[0]).peel_refs();
+                let vector_2 = is_type_diagnostic_item(cx, src_ty, sym::vec_type);
 
-fn is_vec_an_append<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
-    if_chain! {
-        if let ExprKind::MethodCall(method_name, _, exprs, _) = expr.kind;
-        if method_name.ident.as_str() == "extend";
-        let ty = cx.typeck_results().expr_ty(&exprs[0]).peel_refs();
-        if is_type_diagnostic_item(cx, ty, sym::vec_type);
-        if let ExprKind::MethodCall(method_name2, _, _exprs2, _) = &exprs[1].kind;
-        if method_name2.ident.as_str() == "drain";
-        then {
-            return true
+                if method_name.ident.as_str() == "extend"
+                    && src_method.ident.as_str() == "drain"
+                    && range_check
+                    && vector_1
+                    && vector_2
+                {
+                    span_lint_and_help(
+                        cx,
+                        APPEND_INSTEAD_OF_EXTEND,
+                        expr.span,
+                        "use of `vec.extend(other_vec.drain(..))`",
+                        None,
+                        "consider using `vec![].append(&mut vec![]);` instead",
+                    );
+                }
+            }
         }
     }
-    false
 }

tests/ui/append_instead_of_extend.rs

@@ -1,13 +1,28 @@
 #![warn(clippy::append_instead_of_extend)]
 
 fn main() {
-    let mut a = vec![0u8; 1024];
-    let mut b = Vec::new();
+    let mut vec1 = vec![0u8; 1024];
+    let mut vec2: std::vec::Vec<u8> = Vec::new();
 
-    b.extend(a.drain(..));
+    vec2.extend(vec1.drain(..));
 
-    let mut c = vec![0u8, 10];
-    let mut d: std::vec::Vec<u8> = Vec::new();
+    let mut test1 = vec![0u8, 10];
+    let mut test2: std::vec::Vec<u8> = Vec::new();
 
-    c.extend(d.drain(1..3))
+    test2.extend(test1.drain(4..10));
+
+    let mut vec3 = vec![0u8; 104];
+    let mut vec7: std::vec::Vec<u8> = Vec::new();
+
+    vec3.append(&mut vec7);
+
+    let mut vec3 = vec![0u8; 1024];
+    let mut vec4: std::vec::Vec<u8> = Vec::new();
+
+    vec4.extend(vec3.drain(..));
+
+    let mut vec5 = vec![0u8; 1024];
+    let mut vec6: std::vec::Vec<u8> = Vec::new();
+
+    vec5.extend(vec6.drain(..4));
 }

tests/ui/append_instead_of_extend.stderr

@@ -1,11 +1,19 @@
 error: use of `vec.extend(other_vec.drain(..))`
   --> $DIR/append_instead_of_extend.rs:7:5
    |
-LL |     b.extend(a.drain(..));
-   |     ^^^^^^^^^^^^^^^^^^^^^
+LL |     vec2.extend(vec1.drain(..));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::append-instead-of-extend` implied by `-D warnings`
    = help: consider using `vec![].append(&mut vec![]);` instead
 
-error: aborting due to previous error
+error: use of `vec.extend(other_vec.drain(..))`
+  --> $DIR/append_instead_of_extend.rs:22:5
+   |
+LL |     vec4.extend(vec3.drain(..));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider using `vec![].append(&mut vec![]);` instead
+
+error: aborting due to 2 previous errors