feat(code-action): add quickfix to remove redundant parentheses

nixd/lib/Controller/CodeAction.cpp

@@ -51,6 +51,7 @@ void Controller::onCodeAction(const lspserver::CodeActionParams &Params,
         bool IsPreferred = false;
         switch (D.kind()) {
         case nixf::Diagnostic::DK_UnusedDefLet:
+        case nixf::Diagnostic::DK_RedundantParen:
           IsPreferred = true;
           break;
         default:

nixd/tools/nixd/test/code-action/redundant-paren/basic.md

@@ -0,0 +1,86 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+Test basic `remove redundant parens` action for unnecessary parentheses.
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+```nix file:///redundant-paren.nix
+(1)
+```
+
+<-- textDocument/codeAction(2)
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/codeAction",
+   "params":{
+      "textDocument":{
+         "uri":"file:///redundant-paren.nix"
+      },
+      "range":{
+         "start":{
+            "line": 0,
+            "character": 0
+         },
+         "end":{
+            "line":0,
+            "character": 1
+         }
+      },
+      "context":{
+         "diagnostics":[],
+         "triggerKind":2
+      }
+   }
+}
+```
+
+The action should remove both `(` and `)` since the inner expression `1` is simple.
+
+```
+     CHECK: "id": 2,
+     CHECK: "newText": "",
+     CHECK: "range":
+     CHECK:   "end":
+     CHECK:     "character": 1,
+     CHECK:     "line": 0
+     CHECK:   "start":
+     CHECK:     "character": 0,
+     CHECK:     "line": 0
+     CHECK: "newText": "",
+     CHECK: "range":
+     CHECK:   "end":
+     CHECK:     "character": 3,
+     CHECK:     "line": 0
+     CHECK:   "start":
+     CHECK:     "character": 2,
+     CHECK:     "line": 0
+     CHECK: "isPreferred": true,
+     CHECK: "kind": "quickfix",
+     CHECK: "title": "remove ( and )"
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```

nixd/tools/nixd/test/code-action/redundant-paren/multiline.md

@@ -0,0 +1,88 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+Test `remove redundant parens` action with multiline expression.
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+```nix file:///multiline-paren.nix
+(
+  1
+)
+```
+
+<-- textDocument/codeAction(2)
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/codeAction",
+   "params":{
+      "textDocument":{
+         "uri":"file:///multiline-paren.nix"
+      },
+      "range":{
+         "start":{
+            "line": 0,
+            "character": 0
+         },
+         "end":{
+            "line":0,
+            "character": 1
+         }
+      },
+      "context":{
+         "diagnostics":[],
+         "triggerKind":2
+      }
+   }
+}
+```
+
+The action should remove `(` on line 0 and `)` on line 2.
+
+```
+     CHECK: "id": 2,
+     CHECK: "newText": "",
+     CHECK: "range":
+     CHECK:   "end":
+     CHECK:     "character": 1,
+     CHECK:     "line": 0
+     CHECK:   "start":
+     CHECK:     "character": 0,
+     CHECK:     "line": 0
+     CHECK: "newText": "",
+     CHECK: "range":
+     CHECK:   "end":
+     CHECK:     "character": 1,
+     CHECK:     "line": 2
+     CHECK:   "start":
+     CHECK:     "character": 0,
+     CHECK:     "line": 2
+     CHECK: "isPreferred": true,
+     CHECK: "kind": "quickfix",
+     CHECK: "title": "remove ( and )"
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```

nixd/tools/nixd/test/code-action/redundant-paren/needed-paren.md

@@ -0,0 +1,69 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+Test that `remove redundant parens` is NOT offered when parentheses are needed.
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+```nix file:///needed-paren.nix
+(1 + 2)
+```
+
+<-- textDocument/codeAction(2)
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/codeAction",
+   "params":{
+      "textDocument":{
+         "uri":"file:///needed-paren.nix"
+      },
+      "range":{
+         "start":{
+            "line": 0,
+            "character": 0
+         },
+         "end":{
+            "line":0,
+            "character": 1
+         }
+      },
+      "context":{
+         "diagnostics":[],
+         "triggerKind":2
+      }
+   }
+}
+```
+
+No code action should be offered because `1 + 2` is a binary operation, making parentheses meaningful.
+
+```
+     CHECK: "id": 2,
+CHECK-NEXT: "jsonrpc": "2.0",
+CHECK-NEXT: "result": []
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```

nixd/tools/nixd/test/code-action/redundant-paren/nested.md

@@ -0,0 +1,73 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+Test `remove redundant parens` action for nested parentheses `((1))`.
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+```nix file:///nested-paren.nix
+((1))
+```
+
+<-- textDocument/codeAction(2)
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/codeAction",
+   "params":{
+      "textDocument":{
+         "uri":"file:///nested-paren.nix"
+      },
+      "range":{
+         "start":{
+            "line": 0,
+            "character": 0
+         },
+         "end":{
+            "line":0,
+            "character": 5
+         }
+      },
+      "context":{
+         "diagnostics":[],
+         "triggerKind":2
+      }
+   }
+}
+```
+
+Both inner and outer parentheses are redundant, so two quickfix actions should be offered.
+
+```
+     CHECK: "id": 2,
+     CHECK: "isPreferred": true,
+     CHECK: "kind": "quickfix",
+     CHECK: "title": "remove ( and )"
+     CHECK: "isPreferred": true,
+     CHECK: "kind": "quickfix",
+     CHECK: "title": "remove ( and )"
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```