Implement if_same_cond_fn lint

Author: popzxc

CHANGELOG.md

@@ -8,6 +8,9 @@ document.
 
 [3aea860...master](https://github.com/rust-lang/rust-clippy/compare/3aea860...master)
 
+* New lints:
+  * [`ifs_same_cond_fn`] [#4814](https://github.com/rust-lang/rust-clippy/pull/4814)
+
 ## Rust 1.39
 
 Current Beta

README.md

@@ -6,7 +6,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 333 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 334 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_lints/src/copies.rs

@@ -40,6 +40,28 @@ declare_clippy_lint! {
     "consecutive `ifs` with the same condition"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for consecutive `if`s with the same function call.
+    ///
+    /// **Why is this bad?** This is probably a copy & paste error.
+    /// Despite the fact that function can have side effects and `if` works as
+    /// intended, such an approach is implicit and can be considered a "code smell".
+    ///
+    /// **Known problems:** Hopefully none.
+    ///
+    /// **Example:**
+    /// ```ignore
+    /// if foo() {
+    ///     …
+    /// } else if foo() {
+    ///     …
+    /// }
+    /// ```
+    pub IFS_SAME_COND_FN,
+    pedantic,
+    "consecutive `ifs` with the same function call"
+}
+
 declare_clippy_lint! {
     /// **What it does:** Checks for `if/else` with the same body as the *then* part
     /// and the *else* part.
@@ -102,7 +124,7 @@ declare_clippy_lint! {
     "`match` with identical arm bodies"
 }
 
-declare_lint_pass!(CopyAndPaste => [IFS_SAME_COND, IF_SAME_THEN_ELSE, MATCH_SAME_ARMS]);
+declare_lint_pass!(CopyAndPaste => [IFS_SAME_COND, IFS_SAME_COND_FN, IF_SAME_THEN_ELSE, MATCH_SAME_ARMS]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyAndPaste {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
@@ -119,6 +141,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyAndPaste {
             let (conds, blocks) = if_sequence(expr);
             lint_same_then_else(cx, &blocks);
             lint_same_cond(cx, &conds);
+            lint_same_cond_fn(cx, &conds);
             lint_match_arms(cx, expr);
         }
     }
@@ -163,6 +186,34 @@ fn lint_same_cond(cx: &LateContext<'_, '_>, conds: &[&Expr]) {
     }
 }
 
+/// Implementation of `IFS_SAME_COND_FN`.
+fn lint_same_cond_fn(cx: &LateContext<'_, '_>, conds: &[&Expr]) {
+    let hash: &dyn Fn(&&Expr) -> u64 = &|expr| -> u64 {
+        let mut h = SpanlessHash::new(cx, cx.tables);
+        h.hash_expr(expr);
+        h.finish()
+    };
+
+    let eq: &dyn Fn(&&Expr, &&Expr) -> bool = &|&lhs, &rhs| -> bool {
+        // Do not spawn warning if `IFS_SAME_COND` already produced it.
+        if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, rhs) {
+            return false;
+        }
+        SpanlessEq::new(cx).eq_expr(lhs, rhs)
+    };
+
+    for (i, j) in search_same(conds, hash, eq) {
+        span_note_and_lint(
+            cx,
+            IFS_SAME_COND_FN,
+            j.span,
+            "this `if` has the same function call as a previous if",
+            i.span,
+            "same as this",
+        );
+    }
+}
+
 /// Implementation of `MATCH_SAME_ARMS`.
 fn lint_match_arms<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &Expr) {
     fn same_bindings<'tcx>(

clippy_lints/src/lib.rs

@@ -471,6 +471,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         &collapsible_if::COLLAPSIBLE_IF,
         &comparison_chain::COMPARISON_CHAIN,
         &copies::IFS_SAME_COND,
+        &copies::IFS_SAME_COND_FN,
         &copies::IF_SAME_THEN_ELSE,
         &copies::MATCH_SAME_ARMS,
         &copy_iterator::COPY_ITERATOR,
@@ -989,6 +990,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
     store.register_group(true, "clippy::pedantic", Some("clippy_pedantic"), vec![
         LintId::of(&attrs::INLINE_ALWAYS),
         LintId::of(&checked_conversions::CHECKED_CONVERSIONS),
+        LintId::of(&copies::IFS_SAME_COND_FN),
         LintId::of(&copies::MATCH_SAME_ARMS),
         LintId::of(&copy_iterator::COPY_ITERATOR),
         LintId::of(&default_trait_access::DEFAULT_TRAIT_ACCESS),
@@ -1067,6 +1069,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&collapsible_if::COLLAPSIBLE_IF),
         LintId::of(&comparison_chain::COMPARISON_CHAIN),
         LintId::of(&copies::IFS_SAME_COND),
+        LintId::of(&copies::IFS_SAME_COND_FN),
         LintId::of(&copies::IF_SAME_THEN_ELSE),
         LintId::of(&derive::DERIVE_HASH_XOR_EQ),
         LintId::of(&doc::MISSING_SAFETY_DOC),

tests/ui/ifs_same_cond_fn.rs

@@ -0,0 +1,70 @@
+#![warn(clippy::ifs_same_cond_fn)]
+#![allow(clippy::ifs_same_cond)] // This warning is different from `ifs_same_cond`.
+#![allow(clippy::if_same_then_else, clippy::comparison_chain)] // all empty blocks
+
+fn function() -> bool {
+    true
+}
+
+fn fn_arg(_arg: u8) -> bool {
+    true
+}
+
+struct Struct;
+
+impl Struct {
+    fn method(&self) -> bool {
+        true
+    }
+    fn method_arg(&self, _arg: u8) -> bool {
+        true
+    }
+}
+
+fn ifs_same_cond_fn() {
+    let a = 0;
+    let obj = Struct;
+
+    if function() {
+    } else if function() {
+        //~ ERROR ifs same condition
+    }
+
+    if fn_arg(a) {
+    } else if fn_arg(a) {
+        //~ ERROR ifs same condition
+    }
+
+    if obj.method() {
+    } else if obj.method() {
+        //~ ERROR ifs same condition
+    }
+
+    if obj.method_arg(a) {
+    } else if obj.method_arg(a) {
+        //~ ERROR ifs same condition
+    }
+
+    let mut v = vec![1];
+    if v.pop() == None {
+        //~ ERROR ifs same condition
+    } else if v.pop() == None {
+    }
+
+    if v.len() == 42 {
+        //~ ERROR ifs same condition
+    } else if v.len() == 42 {
+    }
+
+    if v.len() == 1 {
+        // ok, different conditions
+    } else if v.len() == 2 {
+    }
+
+    if a == 1 {
+        // ok, warning is on `ifs_same_cond` behalf.
+    } else if a == 1 {
+    }
+}
+
+fn main() {}

tests/ui/ifs_same_cond_fn.stderr

@@ -0,0 +1,75 @@
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:29:15
+   |
+LL |     } else if function() {
+   |               ^^^^^^^^^^
+   |
+   = note: `-D clippy::ifs-same-cond-fn` implied by `-D warnings`
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:28:8
+   |
+LL |     if function() {
+   |        ^^^^^^^^^^
+
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:34:15
+   |
+LL |     } else if fn_arg(a) {
+   |               ^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:33:8
+   |
+LL |     if fn_arg(a) {
+   |        ^^^^^^^^^
+
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:39:15
+   |
+LL |     } else if obj.method() {
+   |               ^^^^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:38:8
+   |
+LL |     if obj.method() {
+   |        ^^^^^^^^^^^^
+
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:44:15
+   |
+LL |     } else if obj.method_arg(a) {
+   |               ^^^^^^^^^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:43:8
+   |
+LL |     if obj.method_arg(a) {
+   |        ^^^^^^^^^^^^^^^^^
+
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:51:15
+   |
+LL |     } else if v.pop() == None {
+   |               ^^^^^^^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:49:8
+   |
+LL |     if v.pop() == None {
+   |        ^^^^^^^^^^^^^^^
+
+error: this `if` has the same function call as a previous if
+  --> $DIR/ifs_same_cond_fn.rs:56:15
+   |
+LL |     } else if v.len() == 42 {
+   |               ^^^^^^^^^^^^^
+   |
+note: same as this
+  --> $DIR/ifs_same_cond_fn.rs:54:8
+   |
+LL |     if v.len() == 42 {
+   |        ^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
+