Add fmod function

src/test/java/org/jetbrains/plugins/ideavim/ex/implementation/functions/floatFunctions/FmodFunctionTest.kt

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2003-2025 The IdeaVim authors
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE.txt file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package org.jetbrains.plugins.ideavim.ex.implementation.functions.floatFunctions
+
+import org.jetbrains.plugins.ideavim.VimTestCase
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.TestInfo
+
+class FmodFunctionTest : VimTestCase() {
+  @BeforeEach
+  override fun setUp(testInfo: TestInfo) {
+    super.setUp(testInfo)
+    configureByText("\n")
+  }
+
+  @Test
+  fun `test fmod returns nan when arguments are zero`() {
+    // The docs say this should return 0
+    assertCommandOutput("echo fmod(0, 0) fmod(42, 0) fmod(0, 42)", "nan nan 0.0")
+  }
+
+  @Test
+  fun `test fmod with integer values`() {
+    assertCommandOutput("echo fmod(12, 7)", "5.0")
+  }
+
+  @Test
+  fun `test fmod with float values`() {
+    assertCommandOutput("echo fmod(12.33, 1.22)", "0.13")
+  }
+
+  @Test
+  fun `test fmod with negative values`() {
+    assertCommandOutput("echo fmod(-12.33, 1.22)", "-0.13")
+  }
+
+  @Test
+  fun `test fmod with string value causes errors`() {
+    enterCommand("echo fmod('42', 7)")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+
+  @Test
+  fun `test fmod with string value causes errors 2`() {
+    enterCommand("echo fmod(42, '7')")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+
+  @Test
+  fun `test fmod with list value causes errors`() {
+    enterCommand("echo fmod([1, 2], 7)")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+
+  @Test
+  fun `test fmod with list value causes errors 2`() {
+    enterCommand("echo fmod(42, [1, 2])")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+
+  @Test
+  fun `test fmod with dictionary value causes errors`() {
+    enterCommand("echo fmod({1: 2}, 7)")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+
+  @Test
+  fun `test fmod with dictionary value causes errors 2`() {
+    enterCommand("echo fmod(42, {1: 2})")
+    assertPluginError(true)
+    assertPluginErrorMessageContains("E808: Number or Float required")
+  }
+}

vim-engine/src/main/kotlin/com/maddyhome/idea/vim/vimscript/model/functions/handlers/floatFunctions/FmodFunctionHandler.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2003-2025 The IdeaVim authors
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE.txt file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package com.maddyhome.idea.vim.vimscript.model.functions.handlers.floatFunctions
+
+import com.intellij.vim.annotations.VimscriptFunction
+
+@VimscriptFunction("fmod")
+internal class FmodFunctionHandler : BinaryFloatFunctionHandlerBase() {
+  override fun invoke(arg1: Double, arg2: Double) = arg1 % arg2
+}

vim-engine/src/main/resources/ksp-generated/engine_vimscript_functions.json

@@ -14,6 +14,7 @@
     "exists": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.variousFunctions.ExistsFunctionHandler",
     "exp": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.floatFunctions.ExpFunctionHandler",
     "floor": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.floatFunctions.FloorFunctionHandler",
+    "fmod": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.floatFunctions.FmodFunctionHandler",
     "funcref": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.varFunctions.FuncrefFunctionHandler",
     "function": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.varFunctions.FunctionFunctionHandler",
     "get": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.GetFunctionHandler",
@@ -40,4 +41,4 @@
     "toupper": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.stringFunctions.ToupperFunctionHandler",
     "trunc": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.floatFunctions.TruncFunctionHandler",
     "xor": "com.maddyhome.idea.vim.vimscript.model.functions.handlers.bitwiseFunctions.XorFunctionHandler"
-}
+}