rust/crates/ide_completion/src/lib.rs

//! `completions` crate provides utilities for generating completions of user input.

mod completions;
mod config;
mod context;
mod item;
mod patterns;
mod render;

#[cfg(test)]
mod tests;

use completions::flyimport::position_for_import;
use ide_db::{
    base_db::FilePosition,
    helpers::{
        import_assets::{LocatedImport, NameToImport},
        insert_use::ImportScope,
    },
    items_locator, RootDatabase,
};
use text_edit::TextEdit;

use crate::{completions::Completions, context::CompletionContext, item::CompletionKind};

pub use crate::{
    config::CompletionConfig,
    item::{CompletionItem, CompletionItemKind, CompletionRelevance, ImportEdit},
};

//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.let` -> `let $0 = expr;`
// - `expr.letm` -> `let mut $0 = expr;`
// - `expr.not` -> `!expr`
// - `expr.dbg` -> `dbg!(expr)`
// - `expr.dbgr` -> `dbg!(&expr)`
// - `expr.call` -> `(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() {}
// }
// ```
//
// And the auto import completions, enabled with the `rust-analyzer.completion.autoimport.enable` setting and the corresponding LSP client capabilities.
// Those are the additional completion options with automatic `use` import and options from all project importable items,
// fuzzy matched against the completion input.
//
// image::https://user-images.githubusercontent.com/48062697/113020667-b72ab880-917a-11eb-8778-716cf26a0eb3.gif[]

/// 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$0
/// }
/// ```
///
/// `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).
///
/// # Speculative Completion Problem
///
/// There's a curious unsolved problem in the current implementation. Often, you
/// want to compute completions on a *slightly different* text document.
///
/// In the simplest case, when the code looks like `let x = `, you want to
/// insert a fake identifier to get a better syntax tree: `let x = complete_me`.
///
/// We do this in `CompletionContext`, and it works OK-enough for *syntax*
/// analysis. However, we might want to, eg, ask for the type of `complete_me`
/// variable, and that's where our current infrastructure breaks down. salsa
/// doesn't allow such "phantom" inputs.
///
/// Another case where this would be instrumental is macro expansion. We want to
/// insert a fake ident and re-expand code. There's `expand_speculative` as a
/// work-around for this.
///
/// A different use-case is completion of injection (examples and links in doc
/// comments). When computing completion for a path in a doc-comment, you want
/// to inject a fake path expression into the item being documented and complete
/// that.
///
/// IntelliJ has CodeFragment/Context infrastructure for that. You can create a
/// temporary PSI node, and say that the context ("parent") of this node is some
/// existing node. Asking for, eg, type of this `CodeFragment` node works
/// correctly, as the underlying infrastructure makes use of contexts to do
/// analysis.
pub fn completions(
    db: &RootDatabase,
    config: &CompletionConfig,
    position: FilePosition,
) -> Option<Completions> {
    let ctx = CompletionContext::new(db, position, config)?;

    if ctx.no_completion_required() {
        cov_mark::hit!(no_completion_required);
        // No work required here.
        return None;
    }

    let mut acc = Completions::default();
    completions::attribute::complete_attribute(&mut acc, &ctx);
    completions::fn_param::complete_fn_param(&mut acc, &ctx);
    completions::keyword::complete_expr_keyword(&mut acc, &ctx);
    completions::snippet::complete_expr_snippet(&mut acc, &ctx);
    completions::snippet::complete_item_snippet(&mut acc, &ctx);
    completions::qualified_path::complete_qualified_path(&mut acc, &ctx);
    completions::unqualified_path::complete_unqualified_path(&mut acc, &ctx);
    completions::dot::complete_dot(&mut acc, &ctx);
    completions::record::complete_record(&mut acc, &ctx);
    completions::pattern::complete_pattern(&mut acc, &ctx);
    completions::postfix::complete_postfix(&mut acc, &ctx);
    completions::trait_impl::complete_trait_impl(&mut acc, &ctx);
    completions::mod_::complete_mod(&mut acc, &ctx);
    completions::flyimport::import_on_the_fly(&mut acc, &ctx);
    completions::lifetime::complete_lifetime(&mut acc, &ctx);
    completions::lifetime::complete_label(&mut acc, &ctx);

    Some(acc)
}

/// Resolves additional completion data at the position given.
pub fn resolve_completion_edits(
    db: &RootDatabase,
    config: &CompletionConfig,
    position: FilePosition,
    full_import_path: &str,
    imported_name: String,
) -> Option<Vec<TextEdit>> {
    let ctx = CompletionContext::new(db, position, config)?;
    let position_for_import = position_for_import(&ctx, None)?;
    let scope = ImportScope::find_insert_use_container_with_macros(position_for_import, &ctx.sema)?;

    let current_module = ctx.sema.scope(position_for_import).module()?;
    let current_crate = current_module.krate();

    let (import_path, item_to_import) = items_locator::items_with_name(
        &ctx.sema,
        current_crate,
        NameToImport::Exact(imported_name),
        items_locator::AssocItemSearch::Include,
        Some(items_locator::DEFAULT_QUERY_SEARCH_LIMIT),
    )
    .filter_map(|candidate| {
        current_module
            .find_use_path_prefixed(db, candidate, config.insert_use.prefix_kind)
            .zip(Some(candidate))
    })
    .find(|(mod_path, _)| mod_path.to_string() == full_import_path)?;
    let import =
        LocatedImport::new(import_path.clone(), item_to_import, item_to_import, Some(import_path));

    ImportEdit { import, scope }.to_text_edit(config.insert_use).map(|edit| vec![edit])
}