Fix array access expression getKtType() bug

For an array access expression e.g., `foo[3]`,
KtFirExpressionTypeProvider first tries
`getReturnTypeForArrayStyleAssignmentTarget(..)` method that determines
the type of the array access expression when it is in the form of "set"
the value. However, the method also returns a non-null result for an
array access expression that reads its value i.e., "get". In this case,
the result of `getKtType()` becomes wrong. This commit lets the method
return a null for the type of "get" array access expression.

analysis/analysis-api-fe10/tests-gen/org/jetbrains/kotlin/analysis/api/fe10/test/cases/generated/cases/components/expressionTypeProvider/Fe10IdeNormalAnalysisSourceModuleHLExpressionTypeTestGenerated.java

@@ -258,5 +258,11 @@ public class Fe10IdeNormalAnalysisSourceModuleHLExpressionTypeTestGenerated exte
         public void testArrayCompoundAssignementTarget() throws Exception {
             runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/arrayCompoundAssignementTarget.kt");
         }
+
+        @Test
+        @TestMetadata("readArrayElement.kt")
+        public void testReadArrayElement() throws Exception {
+            runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.kt");
+        }
     }
 }

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirExpressionTypeProvider.kt

@@ -90,6 +90,7 @@ internal class KtFirExpressionTypeProvider(
         if (expression !is KtArrayAccessExpression) return null
         val assignment = expression.parent as? KtBinaryExpression ?: return null
         if (assignment.operationToken !in KtTokens.ALL_ASSIGNMENTS) return null
+        if (assignment.left != expression) return null
         val setTargetArgumentParameter = fir.argumentMapping?.entries?.last()?.value ?: return null
         return setTargetArgumentParameter.returnTypeRef.coneType.asKtType()
     }

analysis/analysis-api-fir/tests-gen/org/jetbrains/kotlin/analysis/api/fir/test/cases/generated/cases/components/expressionTypeProvider/FirIdeDependentAnalysisSourceModuleHLExpressionTypeTestGenerated.java

@@ -258,5 +258,11 @@ public class FirIdeDependentAnalysisSourceModuleHLExpressionTypeTestGenerated ex
         public void testArrayCompoundAssignementTarget() throws Exception {
             runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/arrayCompoundAssignementTarget.kt");
         }
+
+        @Test
+        @TestMetadata("readArrayElement.kt")
+        public void testReadArrayElement() throws Exception {
+            runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.kt");
+        }
     }
 }

analysis/analysis-api-fir/tests-gen/org/jetbrains/kotlin/analysis/api/fir/test/cases/generated/cases/components/expressionTypeProvider/FirIdeNormalAnalysisSourceModuleHLExpressionTypeTestGenerated.java

@@ -258,5 +258,11 @@ public class FirIdeNormalAnalysisSourceModuleHLExpressionTypeTestGenerated exten
         public void testArrayCompoundAssignementTarget() throws Exception {
             runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/arrayCompoundAssignementTarget.kt");
         }
+
+        @Test
+        @TestMetadata("readArrayElement.kt")
+        public void testReadArrayElement() throws Exception {
+            runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.kt");
+        }
     }
 }

analysis/analysis-api-standalone/tests-gen/org/jetbrains/kotlin/analysis/api/standalone/fir/test/cases/generated/cases/components/expressionTypeProvider/FirStandaloneNormalAnalysisSourceModuleHLExpressionTypeTestGenerated.java

@@ -258,5 +258,11 @@ public class FirStandaloneNormalAnalysisSourceModuleHLExpressionTypeTestGenerate
         public void testArrayCompoundAssignementTarget() throws Exception {
             runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/arrayCompoundAssignementTarget.kt");
         }
+
+        @Test
+        @TestMetadata("readArrayElement.kt")
+        public void testReadArrayElement() throws Exception {
+            runTest("analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.kt");
+        }
     }
 }

analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.kt

@@ -0,0 +1,14 @@
+class FOO {
+    var str: String = ""
+    operator fun plusAssign(tk: String?) {
+        str += tk
+    }
+}
+
+fun main(args: Array<String?>) {
+    val foo: FOO = FOO()
+    if (args.size > 2)
+        foo += <expr>args[2]</expr>
+    else
+        foo += foo.toString()
+}

analysis/analysis-api/testData/components/expressionTypeProvider/expressionType/assignment/readArrayElement.txt

@@ -0,0 +1,2 @@
+expression: args[2]
+type: kotlin.String?