1 files changed, 156 insertions, 0 deletions

diff --git a/crates/ra_analysis/src/completion/completion_context.rs b/crates/ra_analysis/src/completion/completion_context.rs
new file mode 100644
index 000000000..064fbc6f7
--- /dev/null
+++ b/crates/ra_analysis/src/completion/completion_context.rs
@@ -0,0 +1,156 @@
+use ra_editor::find_node_at_offset;
+use ra_text_edit::AtomTextEdit;
+use ra_syntax::{
+    algo::find_leaf_at_offset,
+    ast,
+    AstNode,
+    SyntaxNodeRef,
+    SourceFileNode,
+    TextUnit,
+    SyntaxKind::*,
+};
+use hir::source_binder;
+
+use crate::{db, FilePosition, Cancelable};
+
+/// `CompletionContext` is created early during completion to figure out, where
+/// exactly is the cursor, syntax-wise.
+#[derive(Debug)]
+pub(super) struct CompletionContext<'a> {
+    pub(super) db: &'a db::RootDatabase,
+    pub(super) offset: TextUnit,
+    pub(super) leaf: SyntaxNodeRef<'a>,
+    pub(super) module: Option<hir::Module>,
+    pub(super) enclosing_fn: Option<ast::FnDef<'a>>,
+    pub(super) is_param: bool,
+    /// A single-indent path, like `foo`.
+    pub(super) is_trivial_path: bool,
+    /// If not a trivial, path, the prefix (qualifier).
+    pub(super) path_prefix: Option<hir::Path>,
+    pub(super) after_if: bool,
+    pub(super) is_stmt: bool,
+    /// Something is typed at the "top" level, in module or impl/trait.
+    pub(super) is_new_item: bool,
+}
+
+impl<'a> CompletionContext<'a> {
+    pub(super) fn new(
+        db: &'a db::RootDatabase,
+        original_file: &'a SourceFileNode,
+        position: FilePosition,
+    ) -> Cancelable<Option<CompletionContext<'a>>> {
+        let module = source_binder::module_from_position(db, position)?;
+        let leaf =
+            ctry!(find_leaf_at_offset(original_file.syntax(), position.offset).left_biased());
+        let mut ctx = CompletionContext {
+            db,
+            leaf,
+            offset: position.offset,
+            module,
+            enclosing_fn: None,
+            is_param: false,
+            is_trivial_path: false,
+            path_prefix: None,
+            after_if: false,
+            is_stmt: false,
+            is_new_item: false,
+        };
+        ctx.fill(original_file, position.offset);
+        Ok(Some(ctx))
+    }
+
+    fn fill(&mut self, original_file: &SourceFileNode, offset: TextUnit) {
+        // Insert a fake ident to get a valid parse tree. We will use this file
+        // to determine context, though the original_file will be used for
+        // actual completion.
+        let file = {
+            let edit = AtomTextEdit::insert(offset, "intellijRulezz".to_string());
+            original_file.reparse(&edit)
+        };
+
+        // First, let's try to complete a reference to some declaration.
+        if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), offset) {
+            // Special case, `trait T { fn foo(i_am_a_name_ref) {} }`.
+            // See RFC#1685.
+            if is_node::<ast::Param>(name_ref.syntax()) {
+                self.is_param = true;
+                return;
+            }
+            self.classify_name_ref(&file, name_ref);
+        }
+
+        // Otherwise, see if this is a declaration. We can use heuristics to
+        // suggest declaration names, see `CompletionKind::Magic`.
+        if let Some(name) = find_node_at_offset::<ast::Name>(file.syntax(), offset) {
+            if is_node::<ast::Param>(name.syntax()) {
+                self.is_param = true;
+                return;
+            }
+        }
+    }
+    fn classify_name_ref(&mut self, file: &SourceFileNode, name_ref: ast::NameRef) {
+        let name_range = name_ref.syntax().range();
+        let top_node = name_ref
+            .syntax()
+            .ancestors()
+            .take_while(|it| it.range() == name_range)
+            .last()
+            .unwrap();
+
+        match top_node.parent().map(|it| it.kind()) {
+            Some(SOURCE_FILE) | Some(ITEM_LIST) => {
+                self.is_new_item = true;
+                return;
+            }
+            _ => (),
+        }
+
+        let parent = match name_ref.syntax().parent() {
+            Some(it) => it,
+            None => return,
+        };
+        if let Some(segment) = ast::PathSegment::cast(parent) {
+            let path = segment.parent_path();
+            if let Some(mut path) = hir::Path::from_ast(path) {
+                if !path.is_ident() {
+                    path.segments.pop().unwrap();
+                    self.path_prefix = Some(path);
+                    return;
+                }
+            }
+            if path.qualifier().is_none() {
+                self.is_trivial_path = true;
+                self.enclosing_fn = self
+                    .leaf
+                    .ancestors()
+                    .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+                    .find_map(ast::FnDef::cast);
+
+                self.is_stmt = match name_ref
+                    .syntax()
+                    .ancestors()
+                    .filter_map(ast::ExprStmt::cast)
+                    .next()
+                {
+                    None => false,
+                    Some(expr_stmt) => expr_stmt.syntax().range() == name_ref.syntax().range(),
+                };
+
+                if let Some(off) = name_ref.syntax().range().start().checked_sub(2.into()) {
+                    if let Some(if_expr) = find_node_at_offset::<ast::IfExpr>(file.syntax(), off) {
+                        if if_expr.syntax().range().end() < name_ref.syntax().range().start() {
+                            self.after_if = true;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn is_node<'a, N: AstNode<'a>>(node: SyntaxNodeRef<'a>) -> bool {
+    match node.ancestors().filter_map(N::cast).next() {
+        None => false,
+        Some(n) => n.syntax().range() == node.range(),
+    }
+}