1 files changed, 207 insertions, 0 deletions

diff --git a/crates/ide/src/completion.rs b/crates/ide/src/completion.rs
new file mode 100644
index 000000000..25e580d80
--- /dev/null
+++ b/crates/ide/src/completion.rs
@@ -0,0 +1,207 @@
+mod completion_config;
+mod completion_item;
+mod completion_context;
+mod presentation;
+mod patterns;
+mod generated_features;
+#[cfg(test)]
+mod test_utils;
+
+mod complete_attribute;
+mod complete_dot;
+mod complete_record;
+mod complete_pattern;
+mod complete_fn_param;
+mod complete_keyword;
+mod complete_snippet;
+mod complete_qualified_path;
+mod complete_unqualified_path;
+mod complete_postfix;
+mod complete_macro_in_item_position;
+mod complete_trait_impl;
+
+use ide_db::RootDatabase;
+
+use crate::{
+    completion::{
+        completion_context::CompletionContext,
+        completion_item::{CompletionKind, Completions},
+    },
+    FilePosition,
+};
+
+pub use crate::completion::{
+    completion_config::CompletionConfig,
+    completion_item::{CompletionItem, CompletionItemKind, CompletionScore, InsertTextFormat},
+};
+
+//FIXME: split the following feature into fine-grained features.
+
+// Feature: Magic Completions
+//
+// In addition to usual reference completion, rust-analyzer provides some ✨magic✨
+// completions as well:
+//
+// Keywords like `if`, `else` `while`, `loop` are completed with braces, and cursor
+// is placed at the appropriate position. Even though `if` is easy to type, you
+// still want to complete it, to get ` { }` for free! `return` is inserted with a
+// space or `;` depending on the return type of the function.
+//
+// When completing a function call, `()` are automatically inserted. If a function
+// takes arguments, the cursor is positioned inside the parenthesis.
+//
+// There are postfix completions, which can be triggered by typing something like
+// `foo().if`. The word after `.` determines postfix completion. Possible variants are:
+//
+// - `expr.if` -> `if expr {}` or `if let ... {}` for `Option` or `Result`
+// - `expr.match` -> `match expr {}`
+// - `expr.while` -> `while expr {}` or `while let ... {}` for `Option` or `Result`
+// - `expr.ref` -> `&expr`
+// - `expr.refm` -> `&mut expr`
+// - `expr.not` -> `!expr`
+// - `expr.dbg` -> `dbg!(expr)`
+//
+// There also snippet completions:
+//
+// .Expressions
+// - `pd` -> `eprintln!(" = {:?}", );`
+// - `ppd` -> `eprintln!(" = {:#?}", );`
+//
+// .Items
+// - `tfn` -> `#[test] fn feature(){}`
+// - `tmod` ->
+// ```rust
+// #[cfg(test)]
+// mod tests {
+//     use super::*;
+//
+//     #[test]
+//     fn test_name() {}
+// }
+// ```
+
+/// Main entry point for completion. We run completion as a two-phase process.
+///
+/// First, we look at the position and collect a so-called `CompletionContext.
+/// This is a somewhat messy process, because, during completion, syntax tree is
+/// incomplete and can look really weird.
+///
+/// Once the context is collected, we run a series of completion routines which
+/// look at the context and produce completion items. One subtlety about this
+/// phase is that completion engine should not filter by the substring which is
+/// already present, it should give all possible variants for the identifier at
+/// the caret. In other words, for
+///
+/// ```no-run
+/// fn f() {
+///     let foo = 92;
+///     let _ = bar<|>
+/// }
+/// ```
+///
+/// `foo` *should* be present among the completion variants. Filtering by
+/// identifier prefix/fuzzy match should be done higher in the stack, together
+/// with ordering of completions (currently this is done by the client).
+pub(crate) fn completions(
+    db: &RootDatabase,
+    config: &CompletionConfig,
+    position: FilePosition,
+) -> Option<Completions> {
+    let ctx = CompletionContext::new(db, position, config)?;
+
+    let mut acc = Completions::default();
+    complete_attribute::complete_attribute(&mut acc, &ctx);
+    complete_fn_param::complete_fn_param(&mut acc, &ctx);
+    complete_keyword::complete_expr_keyword(&mut acc, &ctx);
+    complete_keyword::complete_use_tree_keyword(&mut acc, &ctx);
+    complete_snippet::complete_expr_snippet(&mut acc, &ctx);
+    complete_snippet::complete_item_snippet(&mut acc, &ctx);
+    complete_qualified_path::complete_qualified_path(&mut acc, &ctx);
+    complete_unqualified_path::complete_unqualified_path(&mut acc, &ctx);
+    complete_dot::complete_dot(&mut acc, &ctx);
+    complete_record::complete_record(&mut acc, &ctx);
+    complete_pattern::complete_pattern(&mut acc, &ctx);
+    complete_postfix::complete_postfix(&mut acc, &ctx);
+    complete_macro_in_item_position::complete_macro_in_item_position(&mut acc, &ctx);
+    complete_trait_impl::complete_trait_impl(&mut acc, &ctx);
+
+    Some(acc)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::completion::completion_config::CompletionConfig;
+    use crate::mock_analysis::analysis_and_position;
+
+    struct DetailAndDocumentation<'a> {
+        detail: &'a str,
+        documentation: &'a str,
+    }
+
+    fn check_detail_and_documentation(ra_fixture: &str, expected: DetailAndDocumentation) {
+        let (analysis, position) = analysis_and_position(ra_fixture);
+        let config = CompletionConfig::default();
+        let completions = analysis.completions(&config, position).unwrap().unwrap();
+        for item in completions {
+            if item.detail() == Some(expected.detail) {
+                let opt = item.documentation();
+                let doc = opt.as_ref().map(|it| it.as_str());
+                assert_eq!(doc, Some(expected.documentation));
+                return;
+            }
+        }
+        panic!("completion detail not found: {}", expected.detail)
+    }
+
+    #[test]
+    fn test_completion_detail_from_macro_generated_struct_fn_doc_attr() {
+        check_detail_and_documentation(
+            r#"
+            //- /lib.rs
+            macro_rules! bar {
+                () => {
+                    struct Bar;
+                    impl Bar {
+                        #[doc = "Do the foo"]
+                        fn foo(&self) {}
+                    }
+                }
+            }
+
+            bar!();
+
+            fn foo() {
+                let bar = Bar;
+                bar.fo<|>;
+            }
+            "#,
+            DetailAndDocumentation { detail: "fn foo(&self)", documentation: "Do the foo" },
+        );
+    }
+
+    #[test]
+    fn test_completion_detail_from_macro_generated_struct_fn_doc_comment() {
+        check_detail_and_documentation(
+            r#"
+            //- /lib.rs
+            macro_rules! bar {
+                () => {
+                    struct Bar;
+                    impl Bar {
+                        /// Do the foo
+                        fn foo(&self) {}
+                    }
+                }
+            }
+
+            bar!();
+
+            fn foo() {
+                let bar = Bar;
+                bar.fo<|>;
+            }
+            "#,
+            DetailAndDocumentation { detail: "fn foo(&self)", documentation: " Do the foo" },
+        );
+    }
+}