4 files changed, 90 insertions, 7 deletions

diff --git a/crates/ra_ide_api/src/completion/presentation.rs b/crates/ra_ide_api/src/completion/presentation.rs
index 6878008d3..2b3f98482 100644
--- a/crates/ra_ide_api/src/completion/presentation.rs
+++ b/crates/ra_ide_api/src/completion/presentation.rs
@@ -118,7 +118,10 @@ impl Completions {
             .set_documentation(func.docs(ctx.db))
             .detail(detail);
         // If not an import, add parenthesis automatically.
-        if ctx.use_item_syntax.is_none() && !ctx.is_call {
+        if ctx.use_item_syntax.is_none()
+            && !ctx.is_call
+            && ctx.db.feature_flags.get("completion.insertion.add-call-parenthesis")
+        {
             tested_by!(inserts_parens_for_function_calls);
             let snippet =
                 if data.params().is_empty() || data.has_self_param() && data.params().len() == 1 {
diff --git a/crates/ra_ide_api/src/db.rs b/crates/ra_ide_api/src/db.rs
index fc8252e4b..f2e6b8f12 100644
--- a/crates/ra_ide_api/src/db.rs
+++ b/crates/ra_ide_api/src/db.rs
@@ -7,7 +7,7 @@ use ra_db::{
 
 use crate::{
     symbol_index::{self, SymbolsDatabase},
-    LineIndex,
+    FeatureFlags, LineIndex,
 };
 
 #[salsa::database(
@@ -22,6 +22,7 @@ use crate::{
 #[derive(Debug)]
 pub(crate) struct RootDatabase {
     runtime: salsa::Runtime<RootDatabase>,
+    pub(crate) feature_flags: Arc<FeatureFlags>,
     pub(crate) last_gc: time::Instant,
     pub(crate) last_gc_check: time::Instant,
 }
@@ -46,16 +47,17 @@ impl salsa::Database for RootDatabase {
 
 impl Default for RootDatabase {
     fn default() -> RootDatabase {
-        RootDatabase::new(None)
+        RootDatabase::new(None, FeatureFlags::default())
     }
 }
 
 impl RootDatabase {
-    pub fn new(lru_capacity: Option<usize>) -> RootDatabase {
+    pub fn new(lru_capacity: Option<usize>, feature_flags: FeatureFlags) -> RootDatabase {
         let mut db = RootDatabase {
             runtime: salsa::Runtime::default(),
             last_gc: time::Instant::now(),
             last_gc_check: time::Instant::now(),
+            feature_flags: Arc::new(feature_flags),
         };
         db.set_crate_graph_with_durability(Default::default(), Durability::HIGH);
         db.set_local_roots_with_durability(Default::default(), Durability::HIGH);
@@ -74,6 +76,7 @@ impl salsa::ParallelDatabase for RootDatabase {
             runtime: self.runtime.snapshot(self),
             last_gc: self.last_gc,
             last_gc_check: self.last_gc_check,
+            feature_flags: Arc::clone(&self.feature_flags),
         })
     }
 }
diff --git a/crates/ra_ide_api/src/feature_flags.rs b/crates/ra_ide_api/src/feature_flags.rs
new file mode 100644
index 000000000..9f82ac71c
--- /dev/null
+++ b/crates/ra_ide_api/src/feature_flags.rs
@@ -0,0 +1,67 @@
+use rustc_hash::FxHashMap;
+
+/// Feature flags hold fine-grained toggles for all *user-visible* features of
+/// rust-analyzer.
+///
+/// The exists such that users are able to disable any annoying feature (and,
+/// with many users and many features,  some features are bound to be annoying
+/// for some users)
+///
+/// Note that we purposefully use run-time checked strings, and not something
+/// checked at compile time, to keep things simple and flexible.
+///
+/// Also note that, at the moment, `FeatureFlags` also store features for
+/// `ra_lsp_server`. This should be benign layering violation.
+#[derive(Debug)]
+pub struct FeatureFlags {
+    flags: FxHashMap<String, bool>,
+}
+
+impl FeatureFlags {
+    fn new(flags: &[(&str, bool)]) -> FeatureFlags {
+        let flags = flags
+            .iter()
+            .map(|&(name, value)| {
+                check_flag_name(name);
+                (name.to_string(), value)
+            })
+            .collect();
+        FeatureFlags { flags }
+    }
+
+    pub fn set(&mut self, flag: &str, value: bool) -> Result<(), ()> {
+        match self.flags.get_mut(flag) {
+            None => Err(()),
+            Some(slot) => {
+                *slot = value;
+                Ok(())
+            }
+        }
+    }
+
+    pub fn get(&self, flag: &str) -> bool {
+        match self.flags.get(flag) {
+            None => panic!("unknown flag: {:?}", flag),
+            Some(value) => *value,
+        }
+    }
+}
+
+impl Default for FeatureFlags {
+    fn default() -> FeatureFlags {
+        FeatureFlags::new(&[
+            ("lsp.diagnostics", true),
+            ("completion.insertion.add-call-parenthesis", true),
+            ("notifications.workspace-loaded", true),
+        ])
+    }
+}
+
+fn check_flag_name(flag: &str) {
+    for c in flag.bytes() {
+        match c {
+            b'a'..=b'z' | b'-' | b'.' => (),
+            _ => panic!("flag name does not match conventions: {:?}", flag),
+        }
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index fa4ae4379..514dcaf96 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -14,6 +14,7 @@ mod db;
 pub mod mock_analysis;
 mod symbol_index;
 mod change;
+mod feature_flags;
 
 mod status;
 mod completion;
@@ -63,6 +64,7 @@ pub use crate::{
     completion::{CompletionItem, CompletionItemKind, InsertTextFormat},
     diagnostics::Severity,
     display::{file_structure, FunctionSignature, NavigationTarget, StructureNode},
+    feature_flags::FeatureFlags,
     folding_ranges::{Fold, FoldKind},
     hover::HoverResult,
     inlay_hints::{InlayHint, InlayKind},
@@ -247,13 +249,13 @@ pub struct AnalysisHost {
 
 impl Default for AnalysisHost {
     fn default() -> AnalysisHost {
-        AnalysisHost::new(None)
+        AnalysisHost::new(None, FeatureFlags::default())
     }
 }
 
 impl AnalysisHost {
-    pub fn new(lru_capcity: Option<usize>) -> AnalysisHost {
-        AnalysisHost { db: db::RootDatabase::new(lru_capcity) }
+    pub fn new(lru_capcity: Option<usize>, feature_flags: FeatureFlags) -> AnalysisHost {
+        AnalysisHost { db: db::RootDatabase::new(lru_capcity, feature_flags) }
     }
     /// Returns a snapshot of the current state, which you can query for
     /// semantic information.
@@ -261,6 +263,10 @@ impl AnalysisHost {
         Analysis { db: self.db.snapshot() }
     }
 
+    pub fn feature_flags(&self) -> &FeatureFlags {
+        &self.db.feature_flags
+    }
+
     /// Applies changes to the current state of the world. If there are
     /// outstanding snapshots, they will be canceled.
     pub fn apply_change(&mut self, change: AnalysisChange) {
@@ -319,6 +325,10 @@ impl Analysis {
         (host.analysis(), file_id)
     }
 
+    pub fn feature_flags(&self) -> &FeatureFlags {
+        &self.db.feature_flags
+    }
+
     /// Debug info about the current state of the analysis
     pub fn status(&self) -> Cancelable<String> {
         self.with_db(|db| status::status(&*db))