feat: add error documentation links to LSP diagnostics

crates/pyrefly_config/src/error_kind.rs

@@ -273,6 +273,15 @@ impl ErrorKind {
             _ => Severity::Error,
         }
     }
+
+    /// Returns the public documentation URL for this error kind.
+    /// Example: https://pyrefly.org/en/docs/error-kinds/#bad-context-manager
+    pub fn docs_url(self) -> String {
+        format!(
+            "https://pyrefly.org/en/docs/error-kinds/#{}",
+            self.to_name()
+        )
+    }
 }
 
 #[cfg(test)]

pyrefly/lib/error/error.rs

@@ -12,7 +12,9 @@ use std::io::Write;
 use std::path::Path;
 
 use itertools::Itertools;
+use lsp_types::CodeDescription;
 use lsp_types::Diagnostic;
+use lsp_types::Url;
 use pyrefly_python::module::Module;
 use pyrefly_python::module_path::ModulePath;
 use pyrefly_util::display::number_thousands;
@@ -168,6 +170,13 @@ impl Error {
 
     /// Create a diagnostic suitable for use in LSP.
     pub fn to_diagnostic(&self) -> Diagnostic {
+        let code = self.error_kind().to_name().to_owned();
+        let code_description = Url::parse(&format!(
+            "{}",
+            self.error_kind().docs_url()
+        ))
+        .ok()
+        .map(|href| CodeDescription { href });
         Diagnostic {
             range: self.lined_buffer().to_lsp_range(self.range()),
             severity: Some(match self.severity() {
@@ -179,9 +188,8 @@ impl Error {
             }),
             source: Some("Pyrefly".to_owned()),
             message: self.msg().to_owned(),
-            code: Some(lsp_types::NumberOrString::String(
-                self.error_kind().to_name().to_owned(),
-            )),
+            code: Some(lsp_types::NumberOrString::String(code)),
+            code_description,
             ..Default::default()
         }
     }

pyrefly/lib/test/lsp/lsp_interaction/diagnostic.rs

@@ -52,3 +52,86 @@ fn test_unexpected_keyword_range() {
 
     interaction.shutdown();
 }
+
+#[test]
+fn test_error_documentation_links() {
+    let test_files_root = get_test_files_root();
+    let mut interaction = LspInteraction::new();
+    interaction.set_root(test_files_root.path().to_path_buf());
+    interaction.initialize(InitializeSettings {
+        configuration: Some(None),
+        ..Default::default()
+    });
+
+    interaction.server.did_change_configuration();
+
+    interaction.client.expect_configuration_request(2, None);
+    interaction.server.send_configuration_response(2, serde_json::json!([{"pyrefly": {"displayTypeErrors": "force-on"}}, {"pyrefly": {"displayTypeErrors": "force-on"}}]));
+
+    interaction.server.did_open("error_docs_test.py");
+    interaction.server.diagnostic("error_docs_test.py");
+
+    interaction.client.expect_response(Response {
+        id: RequestId::from(2),
+        result: Some(serde_json::json!({
+            "items": [
+                {
+                    "code": "bad-assignment",
+                    "codeDescription": {
+                        "href": "https://pyrefly.org/en/docs/error-kinds/#bad-assignment"
+                    },
+                    "message": "`Literal['']` is not assignable to `int`",
+                    "range": {
+                        "end": {"character": 11, "line": 9},
+                        "start": {"character": 9, "line": 9}
+                    },
+                    "severity": 1,
+                    "source": "Pyrefly"
+                },
+                {
+                    "code": "bad-context-manager",
+                    "codeDescription": {
+                        "href": "https://pyrefly.org/en/docs/error-kinds/#bad-context-manager"
+                    },
+                    "message": "Cannot use `A` as a context manager\n  Object of class `A` has no attribute `__enter__`",
+                    "range": {
+                        "end": {"character": 8, "line": 15},
+                        "start": {"character": 5, "line": 15}
+                    },
+                    "severity": 1,
+                    "source": "Pyrefly"
+                },
+                {
+                    "code": "bad-context-manager",
+                    "codeDescription": {
+                        "href": "https://pyrefly.org/en/docs/error-kinds/#bad-context-manager"
+                    },
+                    "message": "Cannot use `A` as a context manager\n  Object of class `A` has no attribute `__exit__`",
+                    "range": {
+                        "end": {"character": 8, "line": 15},
+                        "start": {"character": 5, "line": 15}
+                    },
+                    "severity": 1,
+                    "source": "Pyrefly"
+                },
+                {
+                    "code": "missing-attribute",
+                    "codeDescription": {
+                        "href": "https://pyrefly.org/en/docs/error-kinds/#missing-attribute"
+                    },
+                    "message": "Object of class `object` has no attribute `nonexistent_method`",
+                    "range": {
+                        "end": {"character": 22, "line": 20},
+                        "start": {"character": 0, "line": 20}
+                    },
+                    "severity": 1,
+                    "source": "Pyrefly"
+                }
+            ],
+            "kind": "full"
+        })),
+        error: None,
+    });
+
+    interaction.shutdown();
+}

pyrefly/lib/test/lsp/lsp_interaction/test_files/error_docs_test.py

@@ -0,0 +1,21 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+# Test file for error documentation links
+# This file contains various error types to test that documentation links are properly included
+
+# Bad assignment error
+x: int = ""
+
+# Bad context manager error  
+class A:
+    pass
+
+with A():
+    pass
+
+# Missing attribute error
+obj = object()
+obj.nonexistent_method()