4 files changed, 42 insertions, 6 deletions

diff --git a/crates/ra_ide/src/completion/completion_item.rs b/crates/ra_ide/src/completion/completion_item.rs
index 61867c0ff..19bbb2517 100644
--- a/crates/ra_ide/src/completion/completion_item.rs
+++ b/crates/ra_ide/src/completion/completion_item.rs
@@ -47,6 +47,10 @@ pub struct CompletionItem {
 
     /// Whether this item is marked as deprecated
     deprecated: bool,
+
+    /// If completing a function call, ask the editor to show parameter popup
+    /// after completion.
+    trigger_call_info: bool,
 }
 
 // We use custom debug for CompletionItem to make `insta`'s diffs more readable.
@@ -139,6 +143,7 @@ impl CompletionItem {
             kind: None,
             text_edit: None,
             deprecated: None,
+            trigger_call_info: None,
         }
     }
     /// What user sees in pop-up in the UI.
@@ -177,6 +182,10 @@ impl CompletionItem {
     pub fn deprecated(&self) -> bool {
         self.deprecated
     }
+
+    pub fn trigger_call_info(&self) -> bool {
+        self.trigger_call_info
+    }
 }
 
 /// A helper to make `CompletionItem`s.
@@ -193,6 +202,7 @@ pub(crate) struct Builder {
     kind: Option<CompletionItemKind>,
     text_edit: Option<TextEdit>,
     deprecated: Option<bool>,
+    trigger_call_info: Option<bool>,
 }
 
 impl Builder {
@@ -221,6 +231,7 @@ impl Builder {
             kind: self.kind,
             completion_kind: self.completion_kind,
             deprecated: self.deprecated.unwrap_or(false),
+            trigger_call_info: self.trigger_call_info.unwrap_or(false),
         }
     }
     pub(crate) fn lookup_by(mut self, lookup: impl Into<String>) -> Builder {
@@ -271,6 +282,10 @@ impl Builder {
         self.deprecated = Some(deprecated);
         self
     }
+    pub(crate) fn trigger_call_info(mut self) -> Builder {
+        self.trigger_call_info = Some(true);
+        self
+    }
 }
 
 impl<'a> Into<CompletionItem> for Builder {
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index dac232a85..d6196a5ce 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -103,7 +103,7 @@ impl Completions {
             }
         };
 
-        // If not an import, add parenthesis automatically.
+        // Add `<>` for generic types
         if ctx.is_path_type
             && !ctx.has_type_args
             && ctx.db.feature_flags.get("completion.insertion.add-call-parenthesis")
@@ -211,7 +211,7 @@ impl Completions {
                 .set_deprecated(is_deprecated(func, ctx.db))
                 .detail(function_signature.to_string());
 
-        // Add `<>` for generic types
+        // If not an import, add parenthesis automatically.
         if ctx.use_item_syntax.is_none()
             && !ctx.is_call
             && ctx.db.feature_flags.get("completion.insertion.add-call-parenthesis")
@@ -221,16 +221,26 @@ impl Completions {
             let (snippet, label) = if params.is_empty() || has_self_param && params.len() == 1 {
                 (format!("{}()$0", name), format!("{}()", name))
             } else {
-                let to_skip = if has_self_param { 1 } else { 0 };
-                let function_params_snippet =
-                    join(
+                builder = builder.trigger_call_info();
+                let snippet = if ctx
+                    .db
+                    .feature_flags
+                    .get("completion.insertion.add-argument-sippets")
+                {
+                    let to_skip = if has_self_param { 1 } else { 0 };
+                    let function_params_snippet = join(
                         function_signature.parameter_names.iter().skip(to_skip).enumerate().map(
                             |(index, param_name)| format!("${{{}:{}}}", index + 1, param_name),
                         ),
                     )
                     .separator(", ")
                     .to_string();
-                (format!("{}({})$0", name, function_params_snippet), format!("{}(…)", name))
+                    format!("{}({})$0", name, function_params_snippet)
+                } else {
+                    format!("{}($0)", name)
+                };
+
+                (snippet, format!("{}(…)", name))
             };
             builder = builder.lookup_by(name).label(label).insert_snippet(snippet);
         }
diff --git a/crates/ra_ide_db/src/feature_flags.rs b/crates/ra_ide_db/src/feature_flags.rs
index 76655f572..d9c9d6cd2 100644
--- a/crates/ra_ide_db/src/feature_flags.rs
+++ b/crates/ra_ide_db/src/feature_flags.rs
@@ -54,6 +54,7 @@ impl Default for FeatureFlags {
         FeatureFlags::new(&[
             ("lsp.diagnostics", true),
             ("completion.insertion.add-call-parenthesis", true),
+            ("completion.insertion.add-argument-sippets", true),
             ("completion.enable-postfix", true),
             ("notifications.workspace-loaded", true),
             ("notifications.cargo-toml-not-found", true),
diff --git a/crates/rust-analyzer/src/conv.rs b/crates/rust-analyzer/src/conv.rs
index eeeb33e8f..fe3b588e4 100644
--- a/crates/rust-analyzer/src/conv.rs
+++ b/crates/rust-analyzer/src/conv.rs
@@ -150,6 +150,16 @@ impl ConvWith<(&LineIndex, LineEndings)> for CompletionItem {
             additional_text_edits: Some(additional_text_edits),
             documentation: self.documentation().map(|it| it.conv()),
             deprecated: Some(self.deprecated()),
+            command: if self.trigger_call_info() {
+                let cmd = lsp_types::Command {
+                    title: "triggerParameterHints".into(),
+                    command: "editor.action.triggerParameterHints".into(),
+                    arguments: None,
+                };
+                Some(cmd)
+            } else {
+                None
+            },
             ..Default::default()
         };