Recommendation 4.3.2 generic types explicit declaration (#314)

### What's done:
  * Added rule logic
  * Added tests
  * Added fixme

diktat-analysis.yml

@@ -259,6 +259,9 @@
   enabled: true
   configuration:
     typeReferenceLength: '25' # max length of type reference
+- name: GENERIC_VARIABLE_WRONG_DECLARATION
+  enabled: true
+  configuration: {}
 # Inspection that checks if string template has redundant curly braces
 - name: STRING_TEMPLATE_CURLY_BRACES
   enabled: true

diktat-rules/src/main/kotlin/generated/WarningNames.kt

@@ -158,6 +158,8 @@ object WarningNames {
 
     const val TYPE_ALIAS: String = "TYPE_ALIAS"
 
+    const val GENERIC_VARIABLE_WRONG_DECLARATION: String = "GENERIC_VARIABLE_WRONG_DECLARATION"
+
     const val STRING_TEMPLATE_CURLY_BRACES: String = "STRING_TEMPLATE_CURLY_BRACES"
 
     const val STRING_TEMPLATE_QUOTES: String = "STRING_TEMPLATE_QUOTES"

diktat-rules/src/main/kotlin/org/cqfn/diktat/ruleset/constants/Warnings.kt

@@ -98,6 +98,7 @@ enum class Warnings(private val canBeAutoCorrected: Boolean, private val warn: S
 
     // ======== chapter 4 ========
     TYPE_ALIAS(false, "variable's type is too complex and should be replaced with typealias"),
+    GENERIC_VARIABLE_WRONG_DECLARATION(true, "variable should have explicit type declaration"),
     STRING_TEMPLATE_CURLY_BRACES(true, "string template has redundant curly braces"),
     STRING_TEMPLATE_QUOTES(true, "string template has redundant quotes"),
     // FixMe: change float literal to BigDecimal? Or kotlin equivalent?

diktat-rules/src/main/kotlin/org/cqfn/diktat/ruleset/rules/DiktatRuleSetProvider.kt

@@ -43,6 +43,7 @@ class DiktatRuleSetProvider(private val diktatConfigFile: String = "diktat-analy
                 ::BlockStructureBraces,
                 ::EmptyBlock,
                 ::EnumsSeparated,
+                ::VariableGenericTypeDeclarationRule,
                 ::SingleLineStatementsRule,
                 ::CommentsFormatting,
                 ::ConsecutiveSpacesRule,

diktat-rules/src/main/kotlin/org/cqfn/diktat/ruleset/rules/VariableGenericTypeDeclarationRule.kt

@@ -0,0 +1,65 @@
+package org.cqfn.diktat.ruleset.rules
+
+import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType.CALL_EXPRESSION
+import com.pinterest.ktlint.core.ast.ElementType.DOT_QUALIFIED_EXPRESSION
+import com.pinterest.ktlint.core.ast.ElementType.PROPERTY
+import com.pinterest.ktlint.core.ast.ElementType.TYPE_ARGUMENT_LIST
+import com.pinterest.ktlint.core.ast.ElementType.TYPE_REFERENCE
+import com.pinterest.ktlint.core.ast.ElementType.VALUE_PARAMETER
+import org.cqfn.diktat.common.config.rules.RulesConfig
+import org.cqfn.diktat.ruleset.constants.Warnings
+import org.cqfn.diktat.ruleset.utils.getAllChildrenWithType
+import org.cqfn.diktat.ruleset.utils.hasChildOfType
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
+import org.jetbrains.kotlin.psi.KtCallExpression
+import org.jetbrains.kotlin.psi.KtParameter
+import org.jetbrains.kotlin.psi.KtProperty
+
+/**
+ * This Rule checks if declaration of a generic variable is appropriate.
+ * Not recommended: val myVariable: Map<Int, String> = emptyMap<Int, String>() or val myVariable = emptyMap<Int, String>()
+ * Recommended: val myVariable: Map<Int, String> = emptyMap()
+ */
+// FIXME: we now don't have access to return types, so we can perform this check only if explicit type is present, but should be able also if it's not.
+class VariableGenericTypeDeclarationRule(private val configRules: List<RulesConfig>) : Rule("variable-generic-type") {
+    private lateinit var emitWarn: ((offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit)
+    private var isFixMode: Boolean = false
+
+    override fun visit(node: ASTNode,
+                       autoCorrect: Boolean,
+                       emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit) {
+        emitWarn = emit
+        isFixMode = autoCorrect
+
+        when(node.elementType) {
+            PROPERTY, VALUE_PARAMETER -> handleProperty(node)
+        }
+    }
+
+    @Suppress("UnsafeCallOnNullableType")
+    private fun handleProperty(node: ASTNode) {
+        val callExpr = node.findChildByType(CALL_EXPRESSION)
+                ?: node.findChildByType(DOT_QUALIFIED_EXPRESSION)?.getAllChildrenWithType(CALL_EXPRESSION)?.lastOrNull()
+
+        val rightSide = (callExpr?.psi as? KtCallExpression)?.typeArgumentList?.arguments
+        val leftSide = if (node.elementType == PROPERTY) {
+            (node.psi as? KtProperty)?.typeReference?.typeElement?.typeArgumentsAsTypes
+        } else {
+            (node.psi as? KtParameter)?.typeReference?.typeElement?.typeArgumentsAsTypes
+        }
+
+        if ((rightSide != null && leftSide != null) &&
+                rightSide.size == leftSide.size &&
+                rightSide.zip(leftSide).all { (first, second) -> first.text == second.text }) {
+            Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnAndFix(configRules, emitWarn, isFixMode,
+                    "type arguments are unnecessary in ${callExpr.text}", node.startOffset, node) {
+                callExpr.removeChild(callExpr.findChildByType(TYPE_ARGUMENT_LIST)!!)
+            }
+        }
+
+        if (leftSide == null && rightSide != null) {
+            Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warn(configRules, emitWarn, isFixMode, node.text, node.startOffset, node)
+        }
+    }
+}

diktat-rules/src/main/resources/diktat-analysis-huawei.yml

@@ -259,6 +259,9 @@
   enabled: true
   configuration:
     typeReferenceLength: '25' # max length of type reference
+- name: GENERIC_VARIABLE_WRONG_DECLARATION
+  enabled: true
+  configuration: {}
 # Inspection that checks if string template has redundant curly braces
 - name: STRING_TEMPLATE_CURLY_BRACES
   enabled: true

diktat-rules/src/main/resources/diktat-analysis.yml

@@ -261,6 +261,9 @@
   enabled: true
   configuration:
     typeReferenceLength: '25' # max length of type reference
+- name: GENERIC_VARIABLE_WRONG_DECLARATION
+  enabled: true
+  configuration: {}
 # Inspection that checks if string template has redundant curly braces
 - name: STRING_TEMPLATE_CURLY_BRACES
   enabled: true

diktat-rules/src/test/kotlin/org/cqfn/diktat/ruleset/chapter4/VariableGenericTypeDeclarationRuleFixTest.kt

@@ -0,0 +1,16 @@
+package org.cqfn.diktat.ruleset.chapter4
+
+import generated.WarningNames
+import org.cqfn.diktat.ruleset.rules.VariableGenericTypeDeclarationRule
+import org.cqfn.diktat.util.FixTestBase
+import org.junit.jupiter.api.Tag
+import org.junit.jupiter.api.Test
+
+class VariableGenericTypeDeclarationRuleFixTest : FixTestBase("test/paragraph4/generics", ::VariableGenericTypeDeclarationRule) {
+
+    @Test
+    @Tag(WarningNames.GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `basic fix test`() {
+        fixAndCompare("VariableGenericTypeDeclarationExpected.kt", "VariableGenericTypeDeclarationTest.kt")
+    }
+}

diktat-rules/src/test/kotlin/org/cqfn/diktat/ruleset/chapter4/VariableGenericTypeDeclarationRuleWarnTest.kt

@@ -0,0 +1,170 @@
+package org.cqfn.diktat.ruleset.chapter4
+
+import com.pinterest.ktlint.core.LintError
+import generated.WarningNames.GENERIC_VARIABLE_WRONG_DECLARATION
+import org.cqfn.diktat.ruleset.constants.Warnings
+import org.cqfn.diktat.ruleset.rules.DIKTAT_RULE_SET_ID
+import org.cqfn.diktat.ruleset.rules.VariableGenericTypeDeclarationRule
+import org.cqfn.diktat.util.LintTestBase
+import org.junit.jupiter.api.Tag
+import org.junit.jupiter.api.Test
+
+class VariableGenericTypeDeclarationRuleWarnTest : LintTestBase(::VariableGenericTypeDeclarationRule) {
+
+    private val ruleId = "$DIKTAT_RULE_SET_ID:variable-generic-type"
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property with generic type good`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   val myVariable: Map<Int, String> = emptyMap()
+                    |   val lazyValue: Map<Int, String> by lazy {
+                    |       println("computed!")
+                    |       emptyMap<Int, String>()
+                    |   }
+                    |   val sideRegex = Regex("<([a-zA-Z, <>?]+)>")
+                    |   val str = someMethod("mapOf<String>")
+                    |   val x = foo.bar<Bar>().baz()
+                    |}
+                """.trimMargin()
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property with generic type bad`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   val myVariable: Map<Int, String> = emptyMap<Int, String>()
+                    |   val any = Array<Any>(3) { "" }
+                    |   val x = foo.bar<Bar>().baz<Some>()
+                    |}
+                """.trimMargin(),
+                LintError(2,4, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} type arguments are unnecessary in emptyMap<Int, String>()", true),
+                LintError(3,4, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} val any = Array<Any>(3) { \"\" }", false),
+                LintError(4,4, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} val x = foo.bar<Bar>().baz<Some>()", false)
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in function as parameter good`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc(myVariable: Map<Int, String> = emptyMap()) {
+                    |       
+                    |   }
+                    |}
+                """.trimMargin()
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in function as parameter bad`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc(myVariable: Map<Int, String> = emptyMap<Int, String>()) {
+                    |       
+                    |   }
+                    |}
+                """.trimMargin(),
+                LintError(2,25, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} type arguments are unnecessary in emptyMap<Int, String>()", true)
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in function good`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc() {
+                    |       val myVariable: Map<Int, String> = emptyMap()
+                    |   }
+                    |}
+                """.trimMargin()
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in function bad`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc() {
+                    |       val myVariable: Map<Int, String> = emptyMap<Int, String>()
+                    |   }
+                    |}
+                """.trimMargin(),
+                LintError(3,8, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} type arguments are unnecessary in emptyMap<Int, String>()", true)
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in class good`() {
+        lintMethod(
+                """
+                    |class SomeClass(val myVariable: Map<Int, String> = emptyMap()) {
+                    |
+                    |}
+                """.trimMargin()
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property in class bad`() {
+        lintMethod(
+                """
+                    |class SomeClass(val myVariable: Map<Int, String> = emptyMap<Int, String>()) {
+                    |
+                    |}
+                """.trimMargin(),
+                LintError(1,17, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} type arguments are unnecessary in emptyMap<Int, String>()", true)
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `property with multiple generics`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc() {
+                    |       val myVariable: Map<Int, Map<String>> = emptyMap<Int, Map<String>>()
+                    |   }
+                    |}
+                """.trimMargin(),
+                LintError(3,8, ruleId,
+                        "${Warnings.GENERIC_VARIABLE_WRONG_DECLARATION.warnText()} type arguments are unnecessary in emptyMap<Int, Map<String>>()", true)
+        )
+    }
+
+    @Test
+    @Tag(GENERIC_VARIABLE_WRONG_DECLARATION)
+    fun `should not trigger`() {
+        lintMethod(
+                """
+                    |class SomeClass {
+                    |   private fun someFunc() {
+                    |       var myVariable: Map<Int, Any> = emptyMap<Int, String>()
+                    |   }
+                    |}
+                """.trimMargin()
+        )
+    }
+}

diktat-rules/src/test/resources/test/paragraph4/generics/VariableGenericTypeDeclarationExpected.kt

@@ -0,0 +1,7 @@
+package test.paragraph4.generics
+
+class SomeClass(val some: Map<Int, String> = emptyMap()) {
+    val myVariable: Map<Int, String> = emptyMap()
+
+    fun someFunc(myVariable: Map<Int, String> = emptyMap()) {}
+}

diktat-rules/src/test/resources/test/paragraph4/generics/VariableGenericTypeDeclarationTest.kt

@@ -0,0 +1,7 @@
+package test.paragraph4.generics
+
+class SomeClass(val some: Map<Int, String> = emptyMap<Int, String>()) {
+    val myVariable: Map<Int, String> = emptyMap<Int, String>()
+
+    fun someFunc(myVariable: Map<Int, String> = emptyMap<Int, String>()) {}
+}

info/available-rules.md

@@ -78,4 +78,6 @@
 |    3 |      3.14.2 | STRING_TEMPLATE_CURLY_BRACES               | Check: warns if there is redundant curly braces in string template<br> Fix: deletes curly braces                 | yes | - | + |
 |    3 |    3.14.2  | STRING_TEMPLATE_QUOTES                      | Check: warns if there are redundant quotes in string template<br> Fix: deletes quotes and $ symbol                   | yes | - | + |
 |    4 |     4.2.2| TYPE_ALIAS                              | Check: if type reference of property is longer than expected                                                                                                                 | yes | typeReferenceLength       |                                                                                     -|
-|    4 |    4.1.1 | FLOAT_IN_ACCURATE_CALCULATIONS          | Checks that floating-point values are not used in arithmetic expressions<br>Fix: no                                                                                          |  no |                         - | Current implementation detects only floating-point constants |
+|    4 |    4.1.1 | FLOAT_IN_ACCURATE_CALCULATIONS          | Checks that floating-point values are not used in arithmetic expressions<br>Fix: no                                                                                          |  no |                         - | Current implementation detects only floating-point constants |
+|    4 |     4.2.2 | TYPE_ALIAS                             | Check: if type reference of property is longer than expected                                                                                                                 | yes | typeReferenceLength       |                                                                                     -|
+|    4 |     4.3.2 | GENERIC_VARIABLE_WRONG_DECLARATION     | Check: warns if variables of generic types don't have explicit type declaration<br>Fix: fixes only variables that have generic declaration on both sides                     | yes | - | + |