8 files changed, 149 insertions, 9 deletions

diff --git a/crates/rust-analyzer/src/diagnostics/test_data/clippy_pass_by_ref.txt b/crates/rust-analyzer/src/diagnostics/test_data/clippy_pass_by_ref.txt
index 5b2e5187a..72f6c5725 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/clippy_pass_by_ref.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/clippy_pass_by_ref.txt
@@ -27,7 +27,24 @@
                     "trivially_copy_pass_by_ref",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "rust-lang.github.io",
+                            ),
+                        ),
+                        port: None,
+                        path: "/rust-clippy/master/index.html",
+                        query: None,
+                        fragment: Some(
+                            "trivially_copy_pass_by_ref",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "clippy",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/test_data/handles_macro_location.txt b/crates/rust-analyzer/src/diagnostics/test_data/handles_macro_location.txt
index 116f0ff73..eb4a6b597 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/handles_macro_location.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/handles_macro_location.txt
@@ -27,7 +27,24 @@
                     "E0277",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "doc.rust-lang.org",
+                            ),
+                        ),
+                        port: None,
+                        path: "/error-index.html",
+                        query: None,
+                        fragment: Some(
+                            "E0277",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "rustc",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/test_data/rustc_incompatible_type_for_trait.txt b/crates/rust-analyzer/src/diagnostics/test_data/rustc_incompatible_type_for_trait.txt
index 2cbf657e5..19f72196d 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/rustc_incompatible_type_for_trait.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/rustc_incompatible_type_for_trait.txt
@@ -27,7 +27,24 @@
                     "E0053",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "doc.rust-lang.org",
+                            ),
+                        ),
+                        port: None,
+                        path: "/error-index.html",
+                        query: None,
+                        fragment: Some(
+                            "E0053",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "rustc",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/test_data/rustc_mismatched_type.txt b/crates/rust-analyzer/src/diagnostics/test_data/rustc_mismatched_type.txt
index 1142dc2ac..15ac95d72 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/rustc_mismatched_type.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/rustc_mismatched_type.txt
@@ -27,7 +27,24 @@
                     "E0308",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "doc.rust-lang.org",
+                            ),
+                        ),
+                        port: None,
+                        path: "/error-index.html",
+                        query: None,
+                        fragment: Some(
+                            "E0308",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "rustc",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/test_data/rustc_wrong_number_of_parameters.txt b/crates/rust-analyzer/src/diagnostics/test_data/rustc_wrong_number_of_parameters.txt
index 782c72dbd..b9650f3e4 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/rustc_wrong_number_of_parameters.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/rustc_wrong_number_of_parameters.txt
@@ -27,7 +27,24 @@
                     "E0061",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "doc.rust-lang.org",
+                            ),
+                        ),
+                        port: None,
+                        path: "/error-index.html",
+                        query: None,
+                        fragment: Some(
+                            "E0061",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "rustc",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/test_data/snap_multi_line_fix.txt b/crates/rust-analyzer/src/diagnostics/test_data/snap_multi_line_fix.txt
index d3f27ab6a..c45f68a91 100644
--- a/crates/rust-analyzer/src/diagnostics/test_data/snap_multi_line_fix.txt
+++ b/crates/rust-analyzer/src/diagnostics/test_data/snap_multi_line_fix.txt
@@ -27,7 +27,24 @@
                     "let_and_return",
                 ),
             ),
-            code_description: None,
+            code_description: Some(
+                CodeDescription {
+                    href: Url {
+                        scheme: "https",
+                        host: Some(
+                            Domain(
+                                "rust-lang.github.io",
+                            ),
+                        ),
+                        port: None,
+                        path: "/rust-clippy/master/index.html",
+                        query: None,
+                        fragment: Some(
+                            "let_and_return",
+                        ),
+                    },
+                },
+            ),
             source: Some(
                 "clippy",
             ),
diff --git a/crates/rust-analyzer/src/diagnostics/to_proto.rs b/crates/rust-analyzer/src/diagnostics/to_proto.rs
index 93bef5c8b..324019614 100644
--- a/crates/rust-analyzer/src/diagnostics/to_proto.rs
+++ b/crates/rust-analyzer/src/diagnostics/to_proto.rs
@@ -211,6 +211,12 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         }
     }
 
+    let code_description = match source.as_str() {
+        "rustc" => rustc_code_description(code.as_deref()),
+        "clippy" => clippy_code_description(code.as_deref()),
+        _ => None,
+    };
+
     primary_spans
         .iter()
         .map(|primary_span| {
@@ -248,7 +254,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                         range: in_macro_location.range,
                         severity,
                         code: code.clone().map(lsp_types::NumberOrString::String),
-                        code_description: None,
+                        code_description: code_description.clone(),
                         source: Some(source.clone()),
                         message: message.clone(),
                         related_information: Some(information_for_additional_diagnostic),
@@ -269,7 +275,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                 range: location.range,
                 severity,
                 code: code.clone().map(lsp_types::NumberOrString::String),
-                code_description: None,
+                code_description: code_description.clone(),
                 source: Some(source.clone()),
                 message,
                 related_information: if related_information.is_empty() {
@@ -292,6 +298,31 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         .collect()
 }
 
+fn rustc_code_description(code: Option<&str>) -> Option<lsp_types::CodeDescription> {
+    code.filter(|code| {
+        let mut chars = code.chars();
+        chars.next().map_or(false, |c| c == 'E')
+            && chars.by_ref().take(4).all(|c| c.is_ascii_digit())
+            && chars.next().is_none()
+    })
+    .and_then(|code| {
+        lsp_types::Url::parse(&format!("https://doc.rust-lang.org/error-index.html#{}", code))
+            .ok()
+            .map(|href| lsp_types::CodeDescription { href })
+    })
+}
+
+fn clippy_code_description(code: Option<&str>) -> Option<lsp_types::CodeDescription> {
+    code.and_then(|code| {
+        lsp_types::Url::parse(&format!(
+            "https://rust-lang.github.io/rust-clippy/master/index.html#{}",
+            code
+        ))
+        .ok()
+        .map(|href| lsp_types::CodeDescription { href })
+    })
+}
+
 #[cfg(test)]
 #[cfg(not(windows))]
 mod tests {
diff --git a/crates/rust-analyzer/src/handlers.rs b/crates/rust-analyzer/src/handlers.rs
index 118e7276f..1cf4139d2 100644
--- a/crates/rust-analyzer/src/handlers.rs
+++ b/crates/rust-analyzer/src/handlers.rs
@@ -1129,7 +1129,14 @@ pub(crate) fn publish_diagnostics(
             range: to_proto::range(&line_index, d.range),
             severity: Some(to_proto::diagnostic_severity(d.severity)),
             code: d.code.map(|d| d.as_str().to_owned()).map(NumberOrString::String),
-            code_description: None,
+            code_description: d.code.and_then(|code| {
+                lsp_types::Url::parse(&format!(
+                    "https://rust-analyzer.github.io/manual.html#{}",
+                    code.as_str()
+                ))
+                .ok()
+                .map(|href| lsp_types::CodeDescription { href })
+            }),
             source: Some("rust-analyzer".to_string()),
             message: d.message,
             related_information: None,