(FIX): add quick fix for unimplemented methods

fixes #536

src/main/kotlin/org/rust/ide/annotator/RustItemsAnnotator.kt

@@ -66,8 +66,12 @@ class RustItemsAnnotator : Annotator {
 
         val notImplemented = mustImplement.keys - implemented.keys
         if (!notImplemented.isEmpty()) {
+            val toImplement = trait.traitBody.traitMethodMemberList.filter { it.name in notImplemented }
+
             holder.createErrorAnnotation(implHeaderTextRange,
-                "Not all trait items implemented, missing: `${notImplemented.first()}`")
+                "Not all trait items implemented, missing: `${notImplemented.first()}`"
+            ).registerFix(ImplementMethods(impl, toImplement))
+
         }
 
         val notMembers = implemented.filterKeys { it !in canImplement }
@@ -86,7 +90,6 @@ private class AddModuleFile(
 
     override fun getFamilyName(): String = text
 
-
     override fun invoke(
         project: Project,
         file: PsiFile,
@@ -103,3 +106,34 @@ private class AddModuleFile(
     }
 
 }
+
+private class ImplementMethods(
+    implBody: RustImplItemElement,
+    private val methods: List<RustTraitMethodMemberElement>
+) : LocalQuickFixAndIntentionActionOnPsiElement(implBody) {
+    init {
+        check(methods.isNotEmpty())
+    }
+
+    override fun getText(): String = "Implement methods"
+
+    override fun getFamilyName(): String = text
+
+    override fun invoke(
+        project: Project,
+        file: PsiFile,
+        editor: Editor?,
+        startElement: PsiElement,
+        endElement: PsiElement
+    ) {
+        val implBody = (startElement as RustImplItemElement).implBody ?: return
+
+        val templateImpl = RustElementFactory.createImplBody(project, methods) ?: return
+        val firstToAdd = templateImpl.implMethodMemberList.firstOrNull() ?: return
+        val lastToAdd = templateImpl.implMethodMemberList.lastOrNull() ?: return
+
+        val lastMethodOrBrace = implBody.implMethodMemberList.lastOrNull() ?: implBody.lbrace
+        implBody.addRangeAfter(firstToAdd, lastToAdd, lastMethodOrBrace)
+    }
+
+}

src/main/kotlin/org/rust/lang/core/psi/RustElementFactory.kt

@@ -23,8 +23,34 @@ object RustElementFactory {
         return createFromText(project, "fn main() { S { $fields }; }")
     }
 
+    fun createImplBody(project: Project, traitMethods: List<RustTraitMethodMemberElement>): RustImplBodyElement? {
+        val m = traitMethods.first()
+        m.copy()
+        val methods = traitMethods
+            .mapNotNull { " ${it.signatureText} {\nunimplemented!()\n}" }
+            .joinToString("\n\n")
+        return createFromText(project, "impl T for S { $methods }")
+    }
+
     private inline fun <reified T : RustCompositeElement> createFromText(project: Project, code: String): T? =
         PsiFileFactory.getInstance(project)
             .createFileFromText("DUMMY.rs", RustLanguage, code)
             ?.childOfType<T>()
+
+    private val RustTraitMethodMemberElement.signatureText: String? get() {
+        // We can't simply take a substring of original method declaration
+        // because of anonymous parameters.
+        val name = name ?: return null
+        val generics = genericParams?.text ?: ""
+
+        val parameters = parameters ?: return null
+        val allArguments = listOfNotNull(parameters.selfArgument?.text) + parameters.parameterList.map {
+            // fix possible anon parameter
+            "${it.pat?.text ?: "_"}: ${it.type?.text ?: "()"}"
+        }
+
+        val ret = retType?.text ?: ""
+        val where = whereClause?.text ?: ""
+        return "fn $name $generics (${allArguments.joinToString(",")}) $ret $where"
+    }
 }

src/test/kotlin/org/rust/ide/annotator/RustItemAnnotatorTest.kt

@@ -16,5 +16,6 @@ class RustItemAnnotatorTest : RustAnnotatorTestBase() {
     }
 
     fun testInvalidTraitImpl() = doTest()
+    fun testInvalidTraitImplFix() = checkQuickFix("Implement methods")
 
 }

src/test/resources/org/rust/ide/annotator/fixtures/items/invalid_trait_impl_fix.rs

@@ -0,0 +1,12 @@
+trait T {
+    fn foo();
+    fn eggs();
+    fn bar() {}
+    fn baz<T>(x: i32, y: String) -> Vec<T> where T: Clone;
+    fn quux(&self) -> Self;
+    fn annon_arg(Arg);
+}
+
+impl T for<caret> () {
+    fn foo() {}
+}

src/test/resources/org/rust/ide/annotator/fixtures/items/invalid_trait_impl_fix_after.rs

@@ -0,0 +1,27 @@
+trait T {
+    fn foo();
+    fn eggs();
+    fn bar() {}
+    fn baz<T>(x: i32, y: String) -> Vec<T> where T: Clone;
+    fn quux(&self) -> Self;
+    fn annon_arg(Arg);
+}
+
+impl T for () {
+    fn foo() {}
+    fn eggs() {
+        unimplemented!()
+    }
+
+    fn baz<T>(x: i32, y: String) -> Vec<T> where T: Clone {
+        unimplemented!()
+    }
+
+    fn quux(&self) -> Self {
+        unimplemented!()
+    }
+
+    fn annon_arg(_: Arg) {
+        unimplemented!()
+    }
+}