[FIR] Add UselessCallOnNotNullChecker

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Basic.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val list1: List<Int> = listOf(1)
+val list = list1.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Basic.txt

@@ -0,0 +1,5 @@
+FILE: Basic.kt
+    public final val list1: R|kotlin/collections/List<kotlin/Int>| = R|kotlin/collections/listOf|<R|kotlin/Int|>(Int(1))
+        public get(): R|kotlin/collections/List<kotlin/Int>|
+    public final val list: R|kotlin/collections/List<kotlin/Int>| = R|/list1|.R|kotlin/collections/orEmpty|<R|kotlin/Int|>()
+        public get(): R|kotlin/collections/List<kotlin/Int>|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullType.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val list1: List<Int> = listOf(1)
+val list = list1.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullType.txt

@@ -0,0 +1,5 @@
+FILE: NotNullType.kt
+    public final val list1: R|kotlin/collections/List<kotlin/Int>| = R|kotlin/collections/listOf|<R|kotlin/Int|>(Int(1))
+        public get(): R|kotlin/collections/List<kotlin/Int>|
+    public final val list: R|kotlin/collections/List<kotlin/Int>| = R|/list1|.R|kotlin/collections/orEmpty|<R|kotlin/Int|>()
+        public get(): R|kotlin/collections/List<kotlin/Int>|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullTypeChain.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val list1: List<Int> = listOf(1)
+val list = list1.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>.map { "$it" }

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullTypeChain.txt

@@ -0,0 +1,8 @@
+FILE: NotNullTypeChain.kt
+    public final val list1: R|kotlin/collections/List<kotlin/Int>| = R|kotlin/collections/listOf|<R|kotlin/Int|>(Int(1))
+        public get(): R|kotlin/collections/List<kotlin/Int>|
+    public final val list: R|kotlin/collections/List<kotlin/String>| = R|/list1|.R|kotlin/collections/orEmpty|<R|kotlin/Int|>().R|kotlin/collections/map|<R|kotlin/Int|, R|kotlin/String|>(<L> = map@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/String| <kind=UNKNOWN>  {
+        ^ R|<local>/it|.R|kotlin/Any.toString|()
+    }
+    )
+        public get(): R|kotlin/collections/List<kotlin/String>|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrBlankSafe.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val s: String? = ""
+val blank = s.isNullOrBlank()

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrBlankSafe.txt

@@ -0,0 +1,5 @@
+FILE: NullOrBlankSafe.kt
+    public final val s: R|kotlin/String?| = String()
+        public get(): R|kotlin/String?|
+    public final val blank: R|kotlin/Boolean| = R|/s|.R|kotlin/text/isNullOrBlank|()
+        public get(): R|kotlin/Boolean|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmpty.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val s = ""
+val empty = s.<!USELESS_CALL_ON_NOT_NULL!>isNullOrEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmpty.txt

@@ -0,0 +1,5 @@
+FILE: NullOrEmpty.kt
+    public final val s: R|kotlin/String| = String()
+        public get(): R|kotlin/String|
+    public final val empty: R|kotlin/Boolean| = R|/s|.R|kotlin/text/isNullOrEmpty|()
+        public get(): R|kotlin/Boolean|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptyFake.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val s: String? = null
+val empty = s.isNullOrEmpty()

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptyFake.txt

@@ -0,0 +1,5 @@
+FILE: NullOrEmptyFake.kt
+    public final val s: R|kotlin/String?| = Null(null)
+        public get(): R|kotlin/String?|
+    public final val empty: R|kotlin/Boolean| = R|/s|.R|kotlin/text/isNullOrEmpty|()
+        public get(): R|kotlin/Boolean|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptySafe.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val s: String? = ""
+val empty = s?.<!USELESS_CALL_ON_NOT_NULL!>isNullOrEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptySafe.txt

@@ -0,0 +1,5 @@
+FILE: NullOrEmptySafe.kt
+    public final val s: R|kotlin/String?| = String()
+        public get(): R|kotlin/String?|
+    public final val empty: R|kotlin/Boolean?| = R|/s|?.{ $subj$.R|kotlin/text/isNullOrEmpty|() }
+        public get(): R|kotlin/Boolean?|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/OrEmptyFake.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val list: List<String>? = null
+val empty = list.orEmpty()

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/OrEmptyFake.txt

@@ -0,0 +1,5 @@
+FILE: OrEmptyFake.kt
+    public final val list: R|kotlin/collections/List<kotlin/String>?| = Null(null)
+        public get(): R|kotlin/collections/List<kotlin/String>?|
+    public final val empty: R|kotlin/collections/List<kotlin/String>| = R|/list|.R|kotlin/collections/orEmpty|<R|kotlin/String|>()
+        public get(): R|kotlin/collections/List<kotlin/String>|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/SafeCall.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val list1: List<Int>? = listOf(1)
+val list = list1?.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/SafeCall.txt

@@ -0,0 +1,5 @@
+FILE: SafeCall.kt
+    public final val list1: R|kotlin/collections/List<kotlin/Int>?| = R|kotlin/collections/listOf|<R|kotlin/Int|>(Int(1))
+        public get(): R|kotlin/collections/List<kotlin/Int>?|
+    public final val list: R|kotlin/collections/List<kotlin/Int>?| = R|/list1|?.{ $subj$.R|kotlin/collections/orEmpty|<R|kotlin/Int|>() }
+        public get(): R|kotlin/collections/List<kotlin/Int>?|

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Sequence.kt

@@ -0,0 +1,5 @@
+// WITH_RUNTIME
+
+fun test(s: Sequence<Int>) {
+    val <!UNUSED_VARIABLE!>foo<!> = s.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>
+}

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Sequence.txt

@@ -0,0 +1,4 @@
+FILE: Sequence.kt
+    public final fun test(s: R|kotlin/sequences/Sequence<kotlin/Int>|): R|kotlin/Unit| {
+        lval foo: R|kotlin/sequences/Sequence<kotlin/Int>| = R|<local>/s|.R|kotlin/sequences/orEmpty|<R|kotlin/Int|>()
+    }

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/String.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+
+val s = ""
+val s1 = s.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>

compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/String.txt

@@ -0,0 +1,5 @@
+FILE: String.kt
+    public final val s: R|kotlin/String| = String()
+        public get(): R|kotlin/String|
+    public final val s1: R|kotlin/String| = R|/s|.R|kotlin/text/orEmpty|()
+        public get(): R|kotlin/String|

compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/ExtendedFirDiagnosticsTestGenerated.java

@@ -349,4 +349,72 @@ public class ExtendedFirDiagnosticsTestGenerated extends AbstractExtendedFirDiag
             runTest("compiler/fir/analysis-tests/testData/extendedCheckers/unused/valueIsNeverRead.kt");
         }
     }
+
+    @TestMetadata("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class UselessCallOnNotNullChecker extends AbstractExtendedFirDiagnosticsTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInUselessCallOnNotNullChecker() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker"), Pattern.compile("^([^.]+)\\.kt$"), null, true);
+        }
+
+        @TestMetadata("Basic.kt")
+        public void testBasic() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Basic.kt");
+        }
+
+        @TestMetadata("NotNullType.kt")
+        public void testNotNullType() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullType.kt");
+        }
+
+        @TestMetadata("NotNullTypeChain.kt")
+        public void testNotNullTypeChain() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullTypeChain.kt");
+        }
+
+        @TestMetadata("NullOrBlankSafe.kt")
+        public void testNullOrBlankSafe() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrBlankSafe.kt");
+        }
+
+        @TestMetadata("NullOrEmpty.kt")
+        public void testNullOrEmpty() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmpty.kt");
+        }
+
+        @TestMetadata("NullOrEmptyFake.kt")
+        public void testNullOrEmptyFake() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptyFake.kt");
+        }
+
+        @TestMetadata("NullOrEmptySafe.kt")
+        public void testNullOrEmptySafe() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptySafe.kt");
+        }
+
+        @TestMetadata("OrEmptyFake.kt")
+        public void testOrEmptyFake() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/OrEmptyFake.kt");
+        }
+
+        @TestMetadata("SafeCall.kt")
+        public void testSafeCall() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/SafeCall.kt");
+        }
+
+        @TestMetadata("Sequence.kt")
+        public void testSequence() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Sequence.kt");
+        }
+
+        @TestMetadata("String.kt")
+        public void testString() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/String.kt");
+        }
+    }
 }

compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/ExtendedFirWithLightTreeDiagnosticsTestGenerated.java

@@ -349,4 +349,72 @@ public class ExtendedFirWithLightTreeDiagnosticsTestGenerated extends AbstractEx
             runTest("compiler/fir/analysis-tests/testData/extendedCheckers/unused/valueIsNeverRead.kt");
         }
     }
+
+    @TestMetadata("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class UselessCallOnNotNullChecker extends AbstractExtendedFirWithLightTreeDiagnosticsTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInUselessCallOnNotNullChecker() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker"), Pattern.compile("^([^.]+)\\.kt$"), null, true);
+        }
+
+        @TestMetadata("Basic.kt")
+        public void testBasic() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Basic.kt");
+        }
+
+        @TestMetadata("NotNullType.kt")
+        public void testNotNullType() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullType.kt");
+        }
+
+        @TestMetadata("NotNullTypeChain.kt")
+        public void testNotNullTypeChain() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NotNullTypeChain.kt");
+        }
+
+        @TestMetadata("NullOrBlankSafe.kt")
+        public void testNullOrBlankSafe() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrBlankSafe.kt");
+        }
+
+        @TestMetadata("NullOrEmpty.kt")
+        public void testNullOrEmpty() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmpty.kt");
+        }
+
+        @TestMetadata("NullOrEmptyFake.kt")
+        public void testNullOrEmptyFake() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptyFake.kt");
+        }
+
+        @TestMetadata("NullOrEmptySafe.kt")
+        public void testNullOrEmptySafe() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptySafe.kt");
+        }
+
+        @TestMetadata("OrEmptyFake.kt")
+        public void testOrEmptyFake() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/OrEmptyFake.kt");
+        }
+
+        @TestMetadata("SafeCall.kt")
+        public void testSafeCall() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/SafeCall.kt");
+        }
+
+        @TestMetadata("Sequence.kt")
+        public void testSequence() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/Sequence.kt");
+        }
+
+        @TestMetadata("String.kt")
+        public void testString() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/extendedCheckers/UselessCallOnNotNullChecker/String.kt");
+        }
+    }
 }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/UselessCallOnNotNullChecker.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.analysis.checkers.extended
+
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.expression.FirQualifiedAccessChecker
+import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.expressions.FirExpression
+import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
+import org.jetbrains.kotlin.fir.references.FirResolvedNamedReference
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.types.ConeNullability
+import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
+import org.jetbrains.kotlin.fir.types.classId
+import org.jetbrains.kotlin.fir.types.coneType
+
+object UselessCallOnNotNullChecker : FirQualifiedAccessChecker() {
+    // todo: add 'call may be reduced' in cases like 's?.isNullOrEmpty()' where 's: String? = ""'
+    override fun check(expression: FirQualifiedAccessExpression, context: CheckerContext, reporter: DiagnosticReporter) {
+        val method = expression.getCallableId() ?: return
+        val calleeOn = expression.explicitReceiver ?: return
+        val calleePackageName = calleeOn.getPackage()
+        val calleeName = method.callableName.asString()
+        if ("$calleePackageName.$calleeName" !in triggerOn) return
+
+        if (calleeOn.getNullability() == ConeNullability.NOT_NULL) {
+            reporter.report(expression.source, FirErrors.USELESS_CALL_ON_NOT_NULL)
+        }
+    }
+
+    private fun FirQualifiedAccessExpression.getCallableId() =
+        ((calleeReference as? FirResolvedNamedReference)?.resolvedSymbol as? FirNamedFunctionSymbol)?.callableId
+
+    private fun FirExpression.getPackage() =
+        (typeRef as? FirResolvedTypeRef)?.coneType?.classId?.packageFqName.toString()
+
+    private fun FirExpression.getNullability() = (typeRef as FirResolvedTypeRef).type.nullability
+
+
+    private val triggerOn = setOf(
+        "kotlin.collections.orEmpty",
+        "kotlin.sequences.orEmpty",
+        "kotlin.text.orEmpty",
+        "kotlin.text.isNullOrEmpty",
+        "kotlin.text.isNullOrEmpty",
+        "kotlin.text.isNullOrBlank",
+        "kotlin.isNullOrBlank",
+        "kotlin.isNullOrEmpty",
+        "kotlin.orEmpty"
+    )
+
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -165,4 +165,5 @@ object FirErrors {
     val ASSIGNED_VALUE_IS_NEVER_READ by warning0<FirSourceElement, PsiElement>()
     val VARIABLE_INITIALIZER_IS_REDUNDANT by warning0<FirSourceElement, PsiElement>()
     val VARIABLE_NEVER_READ by warning0<FirSourceElement, PsiElement>()
+    val USELESS_CALL_ON_NOT_NULL by warning0<FirSourceElement, PsiElement>()
 }

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/checkers/ExtendedExpressionCheckers.kt

@@ -23,6 +23,7 @@ object ExtendedExpressionCheckers : ExpressionCheckers() {
     )
 
     override val qualifiedAccessCheckers: List<FirQualifiedAccessChecker> = listOf(
-        RedundantCallOfConversionMethod
+        RedundantCallOfConversionMethod,
+        UselessCallOnNotNullChecker
     )
 }