Code actions for removing dead code (#989)

* code actions for removing dead code in the current file + each dead item, driven by reanalyze

* changelog and cleanup

* comment and extra match

* comment, and handle another case

Author: zth

CHANGELOG.md

@@ -35,6 +35,7 @@
 - Complete `%todo`. https://github.com/rescript-lang/rescript-vscode/pull/981
 - Add code action for extracting a locally defined module into its own file. https://github.com/rescript-lang/rescript-vscode/pull/983
 - Add code action for expanding catch-all patterns. https://github.com/rescript-lang/rescript-vscode/pull/987
+- Add code actions for removing unused code (per item and for an entire file), driven by `reanalyze`. https://github.com/rescript-lang/rescript-vscode/pull/989
 
 ## 1.50.0
 

client/src/commands/code_analysis.ts

@@ -34,6 +34,22 @@ export type DiagnosticsResultFormat = Array<{
   };
 }>;
 
+enum ClassifiedMessage {
+  Removable,
+  Default,
+}
+
+let classifyMessage = (msg: string) => {
+  if (
+    msg.endsWith(" is never used") ||
+    msg.endsWith(" has no side effects and can be removed")
+  ) {
+    return ClassifiedMessage.Removable;
+  }
+
+  return ClassifiedMessage.Default;
+};
+
 let resultsToDiagnostics = (
   results: DiagnosticsResultFormat,
   diagnosticsResultCodeActions: DiagnosticsResultCodeActionsMap
@@ -91,8 +107,6 @@ let resultsToDiagnostics = (
 
           let codeActionEdit = new WorkspaceEdit();
 
-          // In the future, it would be cool to have an additional code action
-          // here for automatically removing whatever the thing that's dead is.
           codeActionEdit.replace(
             Uri.parse(item.file),
             // Make sure the full line is replaced
@@ -119,6 +133,38 @@ let resultsToDiagnostics = (
           }
         }
       }
+
+      // This heuristic below helps only target dead code that can be removed
+      // safely by just removing its text.
+      if (classifyMessage(item.message) === ClassifiedMessage.Removable) {
+        {
+          let codeAction = new CodeAction("Remove unused");
+          codeAction.kind = CodeActionKind.RefactorRewrite;
+
+          let codeActionEdit = new WorkspaceEdit();
+
+          codeActionEdit.replace(
+            Uri.parse(item.file),
+            new Range(
+              new Position(item.range[0], item.range[1]),
+              new Position(item.range[2], item.range[3])
+            ),
+            ""
+          );
+
+          codeAction.edit = codeActionEdit;
+
+          if (diagnosticsResultCodeActions.has(item.file)) {
+            diagnosticsResultCodeActions
+              .get(item.file)
+              .push({ range: issueLocationRange, codeAction });
+          } else {
+            diagnosticsResultCodeActions.set(item.file, [
+              { range: issueLocationRange, codeAction },
+            ]);
+          }
+        }
+      }
     }
   });
 

client/src/extension.ts

@@ -9,15 +9,17 @@ import {
   Uri,
   Range,
   Position,
+  CodeAction,
+  WorkspaceEdit,
+  CodeActionKind,
 } from "vscode";
 
 import {
   LanguageClient,
   LanguageClientOptions,
   ServerOptions,
   State,
-  Executable,
-  TransportKind
+  TransportKind,
 } from "vscode-languageclient/node";
 
 import * as customCommands from "./commands";
@@ -91,7 +93,11 @@ export function activate(context: ExtensionContext) {
     // If the extension is launched in debug mode then the debug server options are used
     // Otherwise the run options are used
     let serverOptions: ServerOptions = {
-      run: { module: serverModule, args: ["--node-ipc"], transport: TransportKind.ipc },
+      run: {
+        module: serverModule,
+        args: ["--node-ipc"],
+        transport: TransportKind.ipc,
+      },
       debug: {
         module: serverModule,
         args: ["--node-ipc"],
@@ -189,12 +195,31 @@ export function activate(context: ExtensionContext) {
       let availableActions =
         diagnosticsResultCodeActions.get(document.uri.fsPath) ?? [];
 
-      return availableActions
+      const allRemoveActionEdits = availableActions.filter(
+        ({ codeAction }) => codeAction.title === "Remove unused"
+      );
+
+      const actions: CodeAction[] = availableActions
         .filter(
           ({ range }) =>
             range.contains(rangeOrSelection) || range.isEqual(rangeOrSelection)
         )
         .map(({ codeAction }) => codeAction);
+
+      if (allRemoveActionEdits.length > 0) {
+        const removeAllCodeAction = new CodeAction("Remove all unused in file");
+        const edit = new WorkspaceEdit();
+        allRemoveActionEdits.forEach((subEdit) => {
+          subEdit.codeAction.edit.entries().forEach(([uri, [textEdit]]) => {
+            edit.replace(uri, textEdit.range, textEdit.newText);
+          });
+        });
+        removeAllCodeAction.kind = CodeActionKind.RefactorRewrite;
+        removeAllCodeAction.edit = edit;
+        actions.push(removeAllCodeAction);
+      }
+
+      return actions;
     },
   });