1 files changed, 380 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs b/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs
new file mode 100644
index 000000000..d9fe94cb4
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-completion/src/completions/attribute.rs
@@ -0,0 +1,380 @@
+//! Completion for (built-in) attributes, derives and lints.
+//!
+//! This module uses a bit of static metadata to provide completions for builtin-in attributes and lints.
+
+use ide_db::{
+    generated::lints::{
+        Lint, CLIPPY_LINTS, CLIPPY_LINT_GROUPS, DEFAULT_LINTS, FEATURES, RUSTDOC_LINTS,
+    },
+    syntax_helpers::node_ext::parse_tt_as_comma_sep_paths,
+    FxHashMap, SymbolKind,
+};
+use itertools::Itertools;
+use once_cell::sync::Lazy;
+use syntax::{
+    ast::{self, AttrKind},
+    AstNode, SyntaxKind, T,
+};
+
+use crate::{
+    context::{AttrCtx, CompletionContext, PathCompletionCtx, Qualified},
+    item::CompletionItem,
+    Completions,
+};
+
+mod cfg;
+mod derive;
+mod lint;
+mod repr;
+
+pub(crate) use self::derive::complete_derive_path;
+
+/// Complete inputs to known builtin attributes as well as derive attributes
+pub(crate) fn complete_known_attribute_input(
+    acc: &mut Completions,
+    ctx: &CompletionContext<'_>,
+    &colon_prefix: &bool,
+    fake_attribute_under_caret: &ast::Attr,
+) -> Option<()> {
+    let attribute = fake_attribute_under_caret;
+    let name_ref = match attribute.path() {
+        Some(p) => Some(p.as_single_name_ref()?),
+        None => None,
+    };
+    let (path, tt) = name_ref.zip(attribute.token_tree())?;
+    if tt.l_paren_token().is_none() {
+        return None;
+    }
+
+    match path.text().as_str() {
+        "repr" => repr::complete_repr(acc, ctx, tt),
+        "feature" => {
+            lint::complete_lint(acc, ctx, colon_prefix, &parse_tt_as_comma_sep_paths(tt)?, FEATURES)
+        }
+        "allow" | "warn" | "deny" | "forbid" => {
+            let existing_lints = parse_tt_as_comma_sep_paths(tt)?;
+
+            let lints: Vec<Lint> = CLIPPY_LINT_GROUPS
+                .iter()
+                .map(|g| &g.lint)
+                .chain(DEFAULT_LINTS)
+                .chain(CLIPPY_LINTS)
+                .chain(RUSTDOC_LINTS)
+                .cloned()
+                .collect();
+
+            lint::complete_lint(acc, ctx, colon_prefix, &existing_lints, &lints);
+        }
+        "cfg" => cfg::complete_cfg(acc, ctx),
+        _ => (),
+    }
+    Some(())
+}
+
+pub(crate) fn complete_attribute_path(
+    acc: &mut Completions,
+    ctx: &CompletionContext<'_>,
+    path_ctx @ PathCompletionCtx { qualified, .. }: &PathCompletionCtx,
+    &AttrCtx { kind, annotated_item_kind }: &AttrCtx,
+) {
+    let is_inner = kind == AttrKind::Inner;
+
+    match qualified {
+        Qualified::With {
+            resolution: Some(hir::PathResolution::Def(hir::ModuleDef::Module(module))),
+            super_chain_len,
+            ..
+        } => {
+            acc.add_super_keyword(ctx, *super_chain_len);
+
+            for (name, def) in module.scope(ctx.db, Some(ctx.module)) {
+                match def {
+                    hir::ScopeDef::ModuleDef(hir::ModuleDef::Macro(m)) if m.is_attr(ctx.db) => {
+                        acc.add_macro(ctx, path_ctx, m, name)
+                    }
+                    hir::ScopeDef::ModuleDef(hir::ModuleDef::Module(m)) => {
+                        acc.add_module(ctx, path_ctx, m, name)
+                    }
+                    _ => (),
+                }
+            }
+            return;
+        }
+        // fresh use tree with leading colon2, only show crate roots
+        Qualified::Absolute => acc.add_crate_roots(ctx, path_ctx),
+        // only show modules in a fresh UseTree
+        Qualified::No => {
+            ctx.process_all_names(&mut |name, def| match def {
+                hir::ScopeDef::ModuleDef(hir::ModuleDef::Macro(m)) if m.is_attr(ctx.db) => {
+                    acc.add_macro(ctx, path_ctx, m, name)
+                }
+                hir::ScopeDef::ModuleDef(hir::ModuleDef::Module(m)) => {
+                    acc.add_module(ctx, path_ctx, m, name)
+                }
+                _ => (),
+            });
+            acc.add_nameref_keywords_with_colon(ctx);
+        }
+        Qualified::TypeAnchor { .. } | Qualified::With { .. } => {}
+    }
+
+    let attributes = annotated_item_kind.and_then(|kind| {
+        if ast::Expr::can_cast(kind) {
+            Some(EXPR_ATTRIBUTES)
+        } else {
+            KIND_TO_ATTRIBUTES.get(&kind).copied()
+        }
+    });
+
+    let add_completion = |attr_completion: &AttrCompletion| {
+        let mut item =
+            CompletionItem::new(SymbolKind::Attribute, ctx.source_range(), attr_completion.label);
+
+        if let Some(lookup) = attr_completion.lookup {
+            item.lookup_by(lookup);
+        }
+
+        if let Some((snippet, cap)) = attr_completion.snippet.zip(ctx.config.snippet_cap) {
+            item.insert_snippet(cap, snippet);
+        }
+
+        if is_inner || !attr_completion.prefer_inner {
+            item.add_to(acc);
+        }
+    };
+
+    match attributes {
+        Some(applicable) => applicable
+            .iter()
+            .flat_map(|name| ATTRIBUTES.binary_search_by(|attr| attr.key().cmp(name)).ok())
+            .flat_map(|idx| ATTRIBUTES.get(idx))
+            .for_each(add_completion),
+        None if is_inner => ATTRIBUTES.iter().for_each(add_completion),
+        None => ATTRIBUTES.iter().filter(|compl| !compl.prefer_inner).for_each(add_completion),
+    }
+}
+
+struct AttrCompletion {
+    label: &'static str,
+    lookup: Option<&'static str>,
+    snippet: Option<&'static str>,
+    prefer_inner: bool,
+}
+
+impl AttrCompletion {
+    fn key(&self) -> &'static str {
+        self.lookup.unwrap_or(self.label)
+    }
+
+    const fn prefer_inner(self) -> AttrCompletion {
+        AttrCompletion { prefer_inner: true, ..self }
+    }
+}
+
+const fn attr(
+    label: &'static str,
+    lookup: Option<&'static str>,
+    snippet: Option<&'static str>,
+) -> AttrCompletion {
+    AttrCompletion { label, lookup, snippet, prefer_inner: false }
+}
+
+macro_rules! attrs {
+    // attributes applicable to all items
+    [@ { item $($tt:tt)* } {$($acc:tt)*}] => {
+        attrs!(@ { $($tt)* } { $($acc)*, "deprecated", "doc", "dochidden", "docalias", "must_use", "no_mangle" })
+    };
+    // attributes applicable to all adts
+    [@ { adt $($tt:tt)* } {$($acc:tt)*}] => {
+        attrs!(@ { $($tt)* } { $($acc)*, "derive", "repr" })
+    };
+    // attributes applicable to all linkable things aka functions/statics
+    [@ { linkable $($tt:tt)* } {$($acc:tt)*}] => {
+        attrs!(@ { $($tt)* } { $($acc)*, "export_name", "link_name", "link_section" })
+    };
+    // error fallback for nicer error message
+    [@ { $ty:ident $($tt:tt)* } {$($acc:tt)*}] => {
+        compile_error!(concat!("unknown attr subtype ", stringify!($ty)))
+    };
+    // general push down accumulation
+    [@ { $lit:literal $($tt:tt)*} {$($acc:tt)*}] => {
+        attrs!(@ { $($tt)* } { $($acc)*, $lit })
+    };
+    [@ {$($tt:tt)+} {$($tt2:tt)*}] => {
+        compile_error!(concat!("Unexpected input ", stringify!($($tt)+)))
+    };
+    // final output construction
+    [@ {} {$($tt:tt)*}] => { &[$($tt)*] as _ };
+    // starting matcher
+    [$($tt:tt),*] => {
+        attrs!(@ { $($tt)* } { "allow", "cfg", "cfg_attr", "deny", "forbid", "warn" })
+    };
+}
+
+#[rustfmt::skip]
+static KIND_TO_ATTRIBUTES: Lazy<FxHashMap<SyntaxKind, &[&str]>> = Lazy::new(|| {
+    use SyntaxKind::*;
+    [
+        (
+            SOURCE_FILE,
+            attrs!(
+                item,
+                "crate_name", "feature", "no_implicit_prelude", "no_main", "no_std",
+                "recursion_limit", "type_length_limit", "windows_subsystem"
+            ),
+        ),
+        (MODULE, attrs!(item, "macro_use", "no_implicit_prelude", "path")),
+        (ITEM_LIST, attrs!(item, "no_implicit_prelude")),
+        (MACRO_RULES, attrs!(item, "macro_export", "macro_use")),
+        (MACRO_DEF, attrs!(item)),
+        (EXTERN_CRATE, attrs!(item, "macro_use", "no_link")),
+        (USE, attrs!(item)),
+        (TYPE_ALIAS, attrs!(item)),
+        (STRUCT, attrs!(item, adt, "non_exhaustive")),
+        (ENUM, attrs!(item, adt, "non_exhaustive")),
+        (UNION, attrs!(item, adt)),
+        (CONST, attrs!(item)),
+        (
+            FN,
+            attrs!(
+                item, linkable,
+                "cold", "ignore", "inline", "must_use", "panic_handler", "proc_macro",
+                "proc_macro_derive", "proc_macro_attribute", "should_panic", "target_feature",
+                "test", "track_caller"
+            ),
+        ),
+        (STATIC, attrs!(item, linkable, "global_allocator", "used")),
+        (TRAIT, attrs!(item, "must_use")),
+        (IMPL, attrs!(item, "automatically_derived")),
+        (ASSOC_ITEM_LIST, attrs!(item)),
+        (EXTERN_BLOCK, attrs!(item, "link")),
+        (EXTERN_ITEM_LIST, attrs!(item, "link")),
+        (MACRO_CALL, attrs!()),
+        (SELF_PARAM, attrs!()),
+        (PARAM, attrs!()),
+        (RECORD_FIELD, attrs!()),
+        (VARIANT, attrs!("non_exhaustive")),
+        (TYPE_PARAM, attrs!()),
+        (CONST_PARAM, attrs!()),
+        (LIFETIME_PARAM, attrs!()),
+        (LET_STMT, attrs!()),
+        (EXPR_STMT, attrs!()),
+        (LITERAL, attrs!()),
+        (RECORD_EXPR_FIELD_LIST, attrs!()),
+        (RECORD_EXPR_FIELD, attrs!()),
+        (MATCH_ARM_LIST, attrs!()),
+        (MATCH_ARM, attrs!()),
+        (IDENT_PAT, attrs!()),
+        (RECORD_PAT_FIELD, attrs!()),
+    ]
+    .into_iter()
+    .collect()
+});
+const EXPR_ATTRIBUTES: &[&str] = attrs!();
+
+/// <https://doc.rust-lang.org/reference/attributes.html#built-in-attributes-index>
+// Keep these sorted for the binary search!
+const ATTRIBUTES: &[AttrCompletion] = &[
+    attr("allow(…)", Some("allow"), Some("allow(${0:lint})")),
+    attr("automatically_derived", None, None),
+    attr("cfg(…)", Some("cfg"), Some("cfg(${0:predicate})")),
+    attr("cfg_attr(…)", Some("cfg_attr"), Some("cfg_attr(${1:predicate}, ${0:attr})")),
+    attr("cold", None, None),
+    attr(r#"crate_name = """#, Some("crate_name"), Some(r#"crate_name = "${0:crate_name}""#))
+        .prefer_inner(),
+    attr("deny(…)", Some("deny"), Some("deny(${0:lint})")),
+    attr(r#"deprecated"#, Some("deprecated"), Some(r#"deprecated"#)),
+    attr("derive(…)", Some("derive"), Some(r#"derive(${0:Debug})"#)),
+    attr(r#"doc = "…""#, Some("doc"), Some(r#"doc = "${0:docs}""#)),
+    attr(r#"doc(alias = "…")"#, Some("docalias"), Some(r#"doc(alias = "${0:docs}")"#)),
+    attr(r#"doc(hidden)"#, Some("dochidden"), Some(r#"doc(hidden)"#)),
+    attr(
+        r#"export_name = "…""#,
+        Some("export_name"),
+        Some(r#"export_name = "${0:exported_symbol_name}""#),
+    ),
+    attr("feature(…)", Some("feature"), Some("feature(${0:flag})")).prefer_inner(),
+    attr("forbid(…)", Some("forbid"), Some("forbid(${0:lint})")),
+    attr("global_allocator", None, None),
+    attr(r#"ignore = "…""#, Some("ignore"), Some(r#"ignore = "${0:reason}""#)),
+    attr("inline", Some("inline"), Some("inline")),
+    attr("link", None, None),
+    attr(r#"link_name = "…""#, Some("link_name"), Some(r#"link_name = "${0:symbol_name}""#)),
+    attr(
+        r#"link_section = "…""#,
+        Some("link_section"),
+        Some(r#"link_section = "${0:section_name}""#),
+    ),
+    attr("macro_export", None, None),
+    attr("macro_use", None, None),
+    attr(r#"must_use"#, Some("must_use"), Some(r#"must_use"#)),
+    attr("no_implicit_prelude", None, None).prefer_inner(),
+    attr("no_link", None, None).prefer_inner(),
+    attr("no_main", None, None).prefer_inner(),
+    attr("no_mangle", None, None),
+    attr("no_std", None, None).prefer_inner(),
+    attr("non_exhaustive", None, None),
+    attr("panic_handler", None, None),
+    attr(r#"path = "…""#, Some("path"), Some(r#"path ="${0:path}""#)),
+    attr("proc_macro", None, None),
+    attr("proc_macro_attribute", None, None),
+    attr("proc_macro_derive(…)", Some("proc_macro_derive"), Some("proc_macro_derive(${0:Trait})")),
+    attr(
+        r#"recursion_limit = "…""#,
+        Some("recursion_limit"),
+        Some(r#"recursion_limit = "${0:128}""#),
+    )
+    .prefer_inner(),
+    attr("repr(…)", Some("repr"), Some("repr(${0:C})")),
+    attr("should_panic", Some("should_panic"), Some(r#"should_panic"#)),
+    attr(
+        r#"target_feature(enable = "…")"#,
+        Some("target_feature"),
+        Some(r#"target_feature(enable = "${0:feature}")"#),
+    ),
+    attr("test", None, None),
+    attr("track_caller", None, None),
+    attr("type_length_limit = …", Some("type_length_limit"), Some("type_length_limit = ${0:128}"))
+        .prefer_inner(),
+    attr("used", None, None),
+    attr("warn(…)", Some("warn"), Some("warn(${0:lint})")),
+    attr(
+        r#"windows_subsystem = "…""#,
+        Some("windows_subsystem"),
+        Some(r#"windows_subsystem = "${0:subsystem}""#),
+    )
+    .prefer_inner(),
+];
+
+fn parse_comma_sep_expr(input: ast::TokenTree) -> Option<Vec<ast::Expr>> {
+    let r_paren = input.r_paren_token()?;
+    let tokens = input
+        .syntax()
+        .children_with_tokens()
+        .skip(1)
+        .take_while(|it| it.as_token() != Some(&r_paren));
+    let input_expressions = tokens.group_by(|tok| tok.kind() == T![,]);
+    Some(
+        input_expressions
+            .into_iter()
+            .filter_map(|(is_sep, group)| (!is_sep).then(|| group))
+            .filter_map(|mut tokens| syntax::hacks::parse_expr_from_str(&tokens.join("")))
+            .collect::<Vec<ast::Expr>>(),
+    )
+}
+
+#[test]
+fn attributes_are_sorted() {
+    let mut attrs = ATTRIBUTES.iter().map(|attr| attr.key());
+    let mut prev = attrs.next().unwrap();
+
+    attrs.for_each(|next| {
+        assert!(
+            prev < next,
+            r#"ATTRIBUTES array is not sorted, "{}" should come after "{}""#,
+            prev,
+            next
+        );
+        prev = next;
+    });
+}