Much better sublists

src/com/maddyhome/idea/vim/vimscript/model/expressions/OneElementSublistExpression.kt

@@ -24,6 +24,8 @@ import com.maddyhome.idea.vim.ex.ExException
 import com.maddyhome.idea.vim.vimscript.model.VimContext
 import com.maddyhome.idea.vim.vimscript.model.datatypes.VimDataType
 import com.maddyhome.idea.vim.vimscript.model.datatypes.VimDictionary
+import com.maddyhome.idea.vim.vimscript.model.datatypes.VimInt
+import com.maddyhome.idea.vim.vimscript.model.datatypes.VimList
 import com.maddyhome.idea.vim.vimscript.model.datatypes.VimString
 
 data class OneElementSublistExpression(val index: Expression, val expression: Expression) : Expression() {
@@ -38,7 +40,14 @@ data class OneElementSublistExpression(val index: Expression, val expression: Ex
           }\""
         )
     } else {
-      return SublistExpression(index, index, expression).evaluate(editor, context, vimContext)
+      val indexValue = Integer.parseInt(index.evaluate(editor, context, vimContext).asString())
+      if (expressionValue is VimList && (indexValue >= expressionValue.values.size || indexValue < expressionValue.values.size)) {
+        throw ExException("E684: list index out of range: $indexValue")
+      }
+      if (indexValue < 0) {
+        return VimString("")
+      }
+      return SublistExpression(SimpleExpression(VimInt(indexValue)), SimpleExpression(VimInt(indexValue)), SimpleExpression(expressionValue)).evaluate(editor, context, vimContext)
     }
   }
 }

src/com/maddyhome/idea/vim/vimscript/model/expressions/SublistExpression.kt

@@ -27,14 +27,24 @@ data class SublistExpression(val from: Expression?, val to: Expression?, val exp
       toInt += arraySize
     }
     return if (expressionValue is VimList) {
-      if (fromInt <= toInt) {
+      if (fromInt > arraySize) {
+        VimList(mutableListOf())
+      } else if (fromInt == toInt) {
+        expressionValue.values[fromInt]
+      } else if (fromInt <= toInt) {
         VimList(expressionValue.values.subList(fromInt, toInt + 1))
       } else {
         VimList(mutableListOf())
       }
     } else {
-      if (fromInt <= toInt) {
-        VimString(expressionValue.asString().substring(fromInt, toInt + 1))
+      if (fromInt > arraySize) {
+        VimString("")
+      } else if (fromInt <= toInt) {
+        if (toInt > expressionValue.asString().length - 1) {
+          VimString(expressionValue.asString().substring(fromInt))
+        } else {
+          VimString(expressionValue.asString().substring(fromInt, toInt + 1))
+        }
       } else {
         VimString("")
       }

test/org/jetbrains/plugins/ideavim/ex/implementation/expressions/SublistExpressionTest.kt

@@ -0,0 +1,90 @@
+/*
+ * IdeaVim - Vim emulator for IDEs based on the IntelliJ platform
+ * Copyright (C) 2003-2021 The IdeaVim authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.jetbrains.plugins.ideavim.ex.implementation.expressions
+
+import org.jetbrains.plugins.ideavim.VimTestCase
+
+class SublistExpressionTest : VimTestCase() {
+
+  fun `test strung sublist`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[0:1]"))
+    assertExOutput("ab\n")
+  }
+
+  fun `test negative index with sting`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[-1]"))
+    assertExOutput("\n")
+  }
+
+  fun `test index greater than size with string`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[1000]"))
+    assertExOutput("\n")
+  }
+
+  fun `test negative index with list`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo [1, 2][-1]"))
+    assertPluginErrorMessageContains("E684: list index out of range: -1")
+  }
+
+  fun `test index greater than size with list`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo [1, 2][1000]"))
+    assertPluginErrorMessageContains("E684: list index out of range: 1000")
+  }
+
+  fun `test negative first index`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[-1:]"))
+    assertExOutput("c\n")
+  }
+
+  fun `test negative last index`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[0:-2]"))
+    assertExOutput("ab\n")
+  }
+
+  fun `test negative last index2`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[0:-1]"))
+    assertExOutput("abc\n")
+  }
+
+  fun `test last index bigger sting size`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[1:10000]"))
+    assertExOutput("bc\n")
+  }
+
+  fun `test both indexes bigger sting size`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[100:10000]"))
+    assertExOutput("\n")
+  }
+
+  fun `test first index is bigger than second`() {
+    configureByText("\n")
+    typeText(commandToKeys("echo 'abc'[100:10]"))
+    assertExOutput("\n")
+  }
+}