don't lint on if let

don't lint on `if let`

tests/ui/needless_if.fixed

@@ -1,11 +1,13 @@
 //@run-rustfix
 //@aux-build:proc_macros.rs
+#![feature(let_chains)]
 #![allow(
     clippy::blocks_in_if_conditions,
     clippy::if_same_then_else,
     clippy::ifs_same_cond,
     clippy::needless_else,
     clippy::no_effect,
+    clippy::nonminimal_bool,
     unused
 )]
 #![warn(clippy::needless_if)]
@@ -14,21 +16,39 @@ extern crate proc_macros;
 use proc_macros::external;
 use proc_macros::with_span;
 
+fn no_side_effects() -> bool {
+    true
+}
+
+fn has_side_effects(a: &mut u32) -> bool {
+    *a = 1;
+    true
+}
+
 fn main() {
     // Lint
-    (true);
+    
+    // Do not remove the condition
+    no_side_effects();
+    let mut x = 0;
+    has_side_effects(&mut x);
+    assert_eq!(x, 1);
     // Do not lint
     if (true) {
     } else {
     }
+    {
+        return;
+    };
     // Do not lint if `else if` is present
     if (true) {
     } else if (true) {
     }
-    // Ensure clippy does not bork this up, other cases should be added
-    {
-        return;
-    };
+    // Do not lint if any `let` is present
+    if let true = true {}
+    if let true = true && true {}
+    if true && let true = true {}
+    if { if let true = true && true { true } else { false } } && true {}
     external! { if (true) {} }
     with_span! {
         span

tests/ui/needless_if.rs

@@ -1,11 +1,13 @@
 //@run-rustfix
 //@aux-build:proc_macros.rs
+#![feature(let_chains)]
 #![allow(
     clippy::blocks_in_if_conditions,
     clippy::if_same_then_else,
     clippy::ifs_same_cond,
     clippy::needless_else,
     clippy::no_effect,
+    clippy::nonminimal_bool,
     unused
 )]
 #![warn(clippy::needless_if)]
@@ -14,21 +16,42 @@ extern crate proc_macros;
 use proc_macros::external;
 use proc_macros::with_span;
 
+fn no_side_effects() -> bool {
+    true
+}
+
+fn has_side_effects(a: &mut u32) -> bool {
+    *a = 1;
+    true
+}
+
 fn main() {
     // Lint
     if (true) {}
+    // Do not remove the condition
+    if no_side_effects() {}
+    let mut x = 0;
+    if has_side_effects(&mut x) {}
+    assert_eq!(x, 1);
     // Do not lint
     if (true) {
     } else {
     }
+    if {
+        return;
+    } {}
     // Do not lint if `else if` is present
     if (true) {
     } else if (true) {
     }
-    // Ensure clippy does not bork this up, other cases should be added
+    // Do not lint if any `let` is present
+    if let true = true {}
+    if let true = true && true {}
+    if true && let true = true {}
     if {
-        return;
-    } {}
+        if let true = true && true { true } else { false }
+    } && true
+    {}
     external! { if (true) {} }
     with_span! {
         span

tests/ui/needless_if.stderr

@@ -1,13 +1,25 @@
-error: this if branch is empty
-  --> $DIR/needless_if.rs:19:5
+error: this `if` branch is empty
+  --> $DIR/needless_if.rs:30:5
    |
 LL |     if (true) {}
-   |     ^^^^^^^^^^^^ help: you can remove it: `(true);`
+   |     ^^^^^^^^^^^^ help: you can remove it
    |
    = note: `-D clippy::needless-if` implied by `-D warnings`
 
-error: this if branch is empty
-  --> $DIR/needless_if.rs:29:5
+error: this `if` branch is empty
+  --> $DIR/needless_if.rs:32:5
+   |
+LL |     if no_side_effects() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: you can remove it: `no_side_effects();`
+
+error: this `if` branch is empty
+  --> $DIR/needless_if.rs:34:5
+   |
+LL |     if has_side_effects(&mut x) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can remove it: `has_side_effects(&mut x);`
+
+error: this `if` branch is empty
+  --> $DIR/needless_if.rs:40:5
    |
 LL | /     if {
 LL | |         return;
@@ -21,5 +33,5 @@ LL +         return;
 LL +     };
    |
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors