2 files changed, 39 insertions, 16 deletions

diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index af59aa1b6..a004363ee 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -19,7 +19,7 @@ use hir_def::{
 use hir_expand::{
     diagnostics::DiagnosticSink,
     name::{name, AsName},
-    MacroDefId,
+    MacroDefId, MacroDefKind,
 };
 use hir_ty::{
     autoderef, display::HirFormatter, expr::ExprValidator, method_resolution, ApplicationTy,
@@ -762,13 +762,12 @@ impl MacroDef {
 
     /// Indicate it is a proc-macro
     pub fn is_proc_macro(&self) -> bool {
-        match self.id.kind {
-            hir_expand::MacroDefKind::Declarative => false,
-            hir_expand::MacroDefKind::BuiltIn(_) => false,
-            hir_expand::MacroDefKind::BuiltInDerive(_) => false,
-            hir_expand::MacroDefKind::BuiltInEager(_) => false,
-            hir_expand::MacroDefKind::CustomDerive(_) => true,
-        }
+        matches!(self.id.kind, MacroDefKind::CustomDerive(_))
+    }
+
+    /// Indicate it is a derive macro
+    pub fn is_derive_macro(&self) -> bool {
+        matches!(self.id.kind, MacroDefKind::CustomDerive(_) | MacroDefKind::BuiltInDerive(_))
     }
 }
 
diff --git a/crates/ra_ide/src/completion/complete_attribute.rs b/crates/ra_ide/src/completion/complete_attribute.rs
index 8934b45fe..346ba9e7a 100644
--- a/crates/ra_ide/src/completion/complete_attribute.rs
+++ b/crates/ra_ide/src/completion/complete_attribute.rs
@@ -130,11 +130,8 @@ const ATTRIBUTES: &[AttrCompletion] = &[
 ];
 
 fn complete_derive(acc: &mut Completions, ctx: &CompletionContext, derive_input: ast::TokenTree) {
-    // TODO kb autodetect derive macros
-    // https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0/topic/Find.20all.20possible.20derive.20macro.20values.3F/near/195955580
-
     if let Ok(existing_derives) = parse_derive_input(derive_input) {
-        for derive_completion in DERIVE_COMPLETIONS
+        for derive_completion in DEFAULT_DERIVE_COMPLETIONS
             .into_iter()
             .filter(|completion| !existing_derives.contains(completion.label))
         {
@@ -147,9 +144,21 @@ fn complete_derive(acc: &mut Completions, ctx: &CompletionContext, derive_input:
                 label.push_str(", ");
                 label.push_str(dependency);
             }
-            let item = CompletionItem::new(CompletionKind::Attribute, ctx.source_range(), label)
-                .kind(CompletionItemKind::Attribute);
-            acc.add(item);
+            acc.add(
+                CompletionItem::new(CompletionKind::Attribute, ctx.source_range(), label)
+                    .kind(CompletionItemKind::Attribute),
+            );
+        }
+
+        for custom_derive_name in get_derive_names_in_scope(ctx).difference(&existing_derives) {
+            acc.add(
+                CompletionItem::new(
+                    CompletionKind::Attribute,
+                    ctx.source_range(),
+                    custom_derive_name,
+                )
+                .kind(CompletionItemKind::Attribute),
+            );
         }
     }
 }
@@ -174,12 +183,27 @@ fn parse_derive_input(derive_input: ast::TokenTree) -> Result<FxHashSet<String>,
     }
 }
 
+fn get_derive_names_in_scope(ctx: &CompletionContext) -> FxHashSet<String> {
+    let mut result = FxHashSet::default();
+    ctx.scope().process_all_names(&mut |name, scope_def| {
+        if let hir::ScopeDef::MacroDef(mac) = scope_def {
+            if mac.is_derive_macro() {
+                let name_string = name.to_string();
+                result.insert(name_string);
+            }
+        }
+    });
+    result
+}
+
 struct DeriveCompletion {
     label: &'static str,
     dependencies: &'static [&'static str],
 }
 
-const DERIVE_COMPLETIONS: &[DeriveCompletion] = &[
+/// Standard Rust derives and the information about their dependencies
+/// (the dependencies are needed so that the main derive don't break the compilation when added)
+const DEFAULT_DERIVE_COMPLETIONS: &[DeriveCompletion] = &[
     DeriveCompletion { label: "Clone", dependencies: &[] },
     DeriveCompletion { label: "Copy", dependencies: &["Clone"] },
     DeriveCompletion { label: "Debug", dependencies: &[] },