1 files changed, 89 insertions, 0 deletions

diff --git a/crates/ra_ide_api/src/assists.rs b/crates/ra_ide_api/src/assists.rs
new file mode 100644
index 000000000..2da251df5
--- /dev/null
+++ b/crates/ra_ide_api/src/assists.rs
@@ -0,0 +1,89 @@
+mod fill_match_arm;
+
+use ra_syntax::{
+    TextRange, SourceFile, AstNode,
+    algo::find_node_at_offset,
+};
+use ra_ide_api_light::{
+    LocalEdit,
+    assists::{
+        Assist,
+        AssistBuilder
+    }
+};
+use crate::{
+    db::RootDatabase,
+    FileId
+};
+
+/// Return all the assists applicable at the given position.
+pub(crate) fn assists(
+    db: &RootDatabase,
+    file_id: FileId,
+    file: &SourceFile,
+    range: TextRange,
+) -> Vec<LocalEdit> {
+    let ctx = AssistCtx::new(db, file_id, file, range);
+    [fill_match_arm::fill_match_arm]
+        .iter()
+        .filter_map(|&assist| ctx.clone().apply(assist))
+        .collect()
+}
+
+#[derive(Debug, Clone)]
+pub struct AssistCtx<'a> {
+    file_id: FileId,
+    source_file: &'a SourceFile,
+    db: &'a RootDatabase,
+    range: TextRange,
+    should_compute_edit: bool,
+}
+
+impl<'a> AssistCtx<'a> {
+    pub(crate) fn new(
+        db: &'a RootDatabase,
+        file_id: FileId,
+        source_file: &'a SourceFile,
+        range: TextRange,
+    ) -> AssistCtx<'a> {
+        AssistCtx {
+            source_file,
+            file_id,
+            db,
+            range,
+            should_compute_edit: false,
+        }
+    }
+
+    pub fn apply(mut self, assist: fn(AssistCtx) -> Option<Assist>) -> Option<LocalEdit> {
+        self.should_compute_edit = true;
+        match assist(self) {
+            None => None,
+            Some(Assist::Edit(e)) => Some(e),
+            Some(Assist::Applicable) => unreachable!(),
+        }
+    }
+
+    #[allow(unused)]
+    pub fn check(mut self, assist: fn(AssistCtx) -> Option<Assist>) -> bool {
+        self.should_compute_edit = false;
+        match assist(self) {
+            None => false,
+            Some(Assist::Edit(_)) => unreachable!(),
+            Some(Assist::Applicable) => true,
+        }
+    }
+
+    fn build(self, label: impl Into<String>, f: impl FnOnce(&mut AssistBuilder)) -> Option<Assist> {
+        if !self.should_compute_edit {
+            return Some(Assist::Applicable);
+        }
+        let mut edit = AssistBuilder::default();
+        f(&mut edit);
+        Some(edit.build(label))
+    }
+
+    pub(crate) fn node_at_offset<N: AstNode>(&self) -> Option<&'a N> {
+        find_node_at_offset(self.source_file.syntax(), self.range.start())
+    }
+}