[FE 1.0] Report USELESS_IS_CHECK if is expression is always false

^KT-47684 Fixed
2021-07-09 14:03:48 +03:00
parent 785e2f862c
commit 7b5a5f5682
24 changed files with 283 additions and 59 deletions
@@ -0,0 +1,69 @@
+abstract class A
+abstract class B : A()
+
+abstract class AS
+abstract class BS : AS()
+
+interface AI
+interface BI : AI
+
+fun test_1(a: A) {
+    <!USELESS_IS_CHECK("true")!>a is A<!> // always true
+    a is B
+
+    <!USELESS_IS_CHECK("false")!>a is AS<!> // always false
+    <!USELESS_IS_CHECK("false")!>a is BS<!> // always false
+
+    a is AI
+    a is BI
+}
+
+fun test_2(a: A) {
+    <!USELESS_IS_CHECK("false")!>a !is A<!> // always false
+    a !is B
+
+    <!USELESS_IS_CHECK("true")!>a !is AS<!> // always true
+    <!USELESS_IS_CHECK("true")!>a !is BS<!> // always true
+
+    a !is AI
+    a !is BI
+}
+
+fun test_3(a: Any) {
+    if (a is A) {
+        <!USELESS_IS_CHECK("true")!>a is A<!> // always true
+        a is B
+
+        <!USELESS_IS_CHECK("false")!>a is AS<!> // always false
+        <!USELESS_IS_CHECK("false")!>a is BS<!> // always false
+
+        a is AI
+        a is BI
+    }
+}
+
+fun test_4(a: A) {
+    when (a) {
+        <!USELESS_IS_CHECK("true")!>is A<!> -> {} // always true
+        is B -> {}
+
+        <!USELESS_IS_CHECK("false")!>is AS<!> -> {} // always false
+        <!USELESS_IS_CHECK("false")!>is BS<!> -> {} // always false
+
+        is AI -> {}
+        is BI -> {}
+    }
+}
+
+fun test_5(a: A) {
+    when (a) {
+        <!USELESS_IS_CHECK("false")!>!is A<!> -> {} // always false
+        !is B -> {}
+
+        <!USELESS_IS_CHECK("true")!>!is AS<!> -> {} // always true
+        !is BS -> {} // here a may has type AS (by data flow)
+
+        !is AI -> {}
+        !is BI -> {}
+    }
+}