1 files changed, 274 insertions, 0 deletions

diff --git a/crates/ra_ide/src/completion/completion_context.rs b/crates/ra_ide/src/completion/completion_context.rs
new file mode 100644
index 000000000..b8345c91d
--- /dev/null
+++ b/crates/ra_ide/src/completion/completion_context.rs
@@ -0,0 +1,274 @@
+//! FIXME: write short doc here
+
+use ra_syntax::{
+    algo::{find_covering_element, find_node_at_offset},
+    ast, AstNode, Parse, SourceFile,
+    SyntaxKind::*,
+    SyntaxNode, SyntaxToken, TextRange, TextUnit,
+};
+use ra_text_edit::AtomTextEdit;
+
+use crate::{db, FilePosition};
+
+/// `CompletionContext` is created early during completion to figure out, where
+/// exactly is the cursor, syntax-wise.
+#[derive(Debug)]
+pub(crate) struct CompletionContext<'a> {
+    pub(super) db: &'a db::RootDatabase,
+    pub(super) analyzer: hir::SourceAnalyzer,
+    pub(super) offset: TextUnit,
+    pub(super) token: SyntaxToken,
+    pub(super) module: Option<hir::Module>,
+    pub(super) function_syntax: Option<ast::FnDef>,
+    pub(super) use_item_syntax: Option<ast::UseItem>,
+    pub(super) record_lit_syntax: Option<ast::RecordLit>,
+    pub(super) record_lit_pat: Option<ast::RecordPat>,
+    pub(super) is_param: bool,
+    /// If a name-binding or reference to a const in a pattern.
+    /// Irrefutable patterns (like let) are excluded.
+    pub(super) is_pat_binding: bool,
+    /// A single-indent path, like `foo`. `::foo` should not be considered a trivial path.
+    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,
+    /// `true` if we are a statement or a last expr in the block.
+    pub(super) can_be_stmt: bool,
+    /// Something is typed at the "top" level, in module or impl/trait.
+    pub(super) is_new_item: bool,
+    /// The receiver if this is a field or method access, i.e. writing something.<|>
+    pub(super) dot_receiver: Option<ast::Expr>,
+    pub(super) dot_receiver_is_ambiguous_float_literal: bool,
+    /// If this is a call (method or function) in particular, i.e. the () are already there.
+    pub(super) is_call: bool,
+    pub(super) is_path_type: bool,
+    pub(super) has_type_args: bool,
+}
+
+impl<'a> CompletionContext<'a> {
+    pub(super) fn new(
+        db: &'a db::RootDatabase,
+        original_parse: &'a Parse<ast::SourceFile>,
+        position: FilePosition,
+    ) -> Option<CompletionContext<'a>> {
+        let src = hir::ModuleSource::from_position(db, position);
+        let module = hir::Module::from_definition(
+            db,
+            hir::Source { file_id: position.file_id.into(), value: src },
+        );
+        let token =
+            original_parse.tree().syntax().token_at_offset(position.offset).left_biased()?;
+        let analyzer = hir::SourceAnalyzer::new(
+            db,
+            hir::Source::new(position.file_id.into(), &token.parent()),
+            Some(position.offset),
+        );
+        let mut ctx = CompletionContext {
+            db,
+            analyzer,
+            token,
+            offset: position.offset,
+            module,
+            function_syntax: None,
+            use_item_syntax: None,
+            record_lit_syntax: None,
+            record_lit_pat: None,
+            is_param: false,
+            is_pat_binding: false,
+            is_trivial_path: false,
+            path_prefix: None,
+            after_if: false,
+            can_be_stmt: false,
+            is_new_item: false,
+            dot_receiver: None,
+            is_call: false,
+            is_path_type: false,
+            has_type_args: false,
+            dot_receiver_is_ambiguous_float_literal: false,
+        };
+        ctx.fill(&original_parse, position.offset);
+        Some(ctx)
+    }
+
+    // The range of the identifier that is being completed.
+    pub(crate) fn source_range(&self) -> TextRange {
+        match self.token.kind() {
+            // workaroud when completion is triggered by trigger characters.
+            IDENT => self.token.text_range(),
+            _ => TextRange::offset_len(self.offset, 0.into()),
+        }
+    }
+
+    fn fill(&mut self, original_parse: &'a Parse<ast::SourceFile>, 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_parse.reparse(&edit).tree()
+        };
+
+        // 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(original_parse.tree(), 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 let Some(bind_pat) = name.syntax().ancestors().find_map(ast::BindPat::cast) {
+                let parent = bind_pat.syntax().parent();
+                if parent.clone().and_then(ast::MatchArm::cast).is_some()
+                    || parent.and_then(ast::Condition::cast).is_some()
+                {
+                    self.is_pat_binding = true;
+                }
+            }
+            if is_node::<ast::Param>(name.syntax()) {
+                self.is_param = true;
+                return;
+            }
+            if name.syntax().ancestors().find_map(ast::RecordFieldPatList::cast).is_some() {
+                self.record_lit_pat =
+                    find_node_at_offset(original_parse.tree().syntax(), self.offset);
+            }
+        }
+    }
+
+    fn classify_name_ref(&mut self, original_file: SourceFile, name_ref: ast::NameRef) {
+        let name_range = name_ref.syntax().text_range();
+        if name_ref.syntax().parent().and_then(ast::RecordField::cast).is_some() {
+            self.record_lit_syntax = find_node_at_offset(original_file.syntax(), self.offset);
+        }
+
+        let top_node = name_ref
+            .syntax()
+            .ancestors()
+            .take_while(|it| it.text_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;
+            }
+            _ => (),
+        }
+
+        self.use_item_syntax = self.token.parent().ancestors().find_map(ast::UseItem::cast);
+
+        self.function_syntax = self
+            .token
+            .parent()
+            .ancestors()
+            .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+            .find_map(ast::FnDef::cast);
+
+        let parent = match name_ref.syntax().parent() {
+            Some(it) => it,
+            None => return,
+        };
+
+        if let Some(segment) = ast::PathSegment::cast(parent.clone()) {
+            let path = segment.parent_path();
+            self.is_call = path
+                .syntax()
+                .parent()
+                .and_then(ast::PathExpr::cast)
+                .and_then(|it| it.syntax().parent().and_then(ast::CallExpr::cast))
+                .is_some();
+
+            self.is_path_type = path.syntax().parent().and_then(ast::PathType::cast).is_some();
+            self.has_type_args = segment.type_arg_list().is_some();
+
+            if let Some(mut path) = hir::Path::from_ast(path.clone()) {
+                if !path.is_ident() {
+                    path.segments.pop().unwrap();
+                    self.path_prefix = Some(path);
+                    return;
+                }
+            }
+
+            if path.qualifier().is_none() {
+                self.is_trivial_path = true;
+
+                // Find either enclosing expr statement (thing with `;`) or a
+                // block. If block, check that we are the last expr.
+                self.can_be_stmt = name_ref
+                    .syntax()
+                    .ancestors()
+                    .find_map(|node| {
+                        if let Some(stmt) = ast::ExprStmt::cast(node.clone()) {
+                            return Some(
+                                stmt.syntax().text_range() == name_ref.syntax().text_range(),
+                            );
+                        }
+                        if let Some(block) = ast::Block::cast(node) {
+                            return Some(
+                                block.expr().map(|e| e.syntax().text_range())
+                                    == Some(name_ref.syntax().text_range()),
+                            );
+                        }
+                        None
+                    })
+                    .unwrap_or(false);
+
+                if let Some(off) = name_ref.syntax().text_range().start().checked_sub(2.into()) {
+                    if let Some(if_expr) =
+                        find_node_at_offset::<ast::IfExpr>(original_file.syntax(), off)
+                    {
+                        if if_expr.syntax().text_range().end()
+                            < name_ref.syntax().text_range().start()
+                        {
+                            self.after_if = true;
+                        }
+                    }
+                }
+            }
+        }
+        if let Some(field_expr) = ast::FieldExpr::cast(parent.clone()) {
+            // The receiver comes before the point of insertion of the fake
+            // ident, so it should have the same range in the non-modified file
+            self.dot_receiver = field_expr
+                .expr()
+                .map(|e| e.syntax().text_range())
+                .and_then(|r| find_node_with_range(original_file.syntax(), r));
+            self.dot_receiver_is_ambiguous_float_literal = if let Some(ast::Expr::Literal(l)) =
+                &self.dot_receiver
+            {
+                match l.kind() {
+                    ast::LiteralKind::FloatNumber { suffix: _ } => l.token().text().ends_with('.'),
+                    _ => false,
+                }
+            } else {
+                false
+            }
+        }
+        if let Some(method_call_expr) = ast::MethodCallExpr::cast(parent) {
+            // As above
+            self.dot_receiver = method_call_expr
+                .expr()
+                .map(|e| e.syntax().text_range())
+                .and_then(|r| find_node_with_range(original_file.syntax(), r));
+            self.is_call = true;
+        }
+    }
+}
+
+fn find_node_with_range<N: AstNode>(syntax: &SyntaxNode, range: TextRange) -> Option<N> {
+    find_covering_element(syntax, range).ancestors().find_map(N::cast)
+}
+
+fn is_node<N: AstNode>(node: &SyntaxNode) -> bool {
+    match node.ancestors().find_map(N::cast) {
+        None => false,
+        Some(n) => n.syntax().text_range() == node.text_range(),
+    }
+}