1 files changed, 116 insertions, 0 deletions

diff --git a/crates/completion/src/render/macro_.rs b/crates/completion/src/render/macro_.rs
new file mode 100644
index 000000000..bcf94f47e
--- /dev/null
+++ b/crates/completion/src/render/macro_.rs
@@ -0,0 +1,116 @@
+use hir::{Documentation, HasAttrs, HasSource};
+use syntax::display::macro_label;
+use test_utils::mark;
+
+use crate::{
+    item::{CompletionItem, CompletionItemKind, CompletionKind},
+    render::RenderContext,
+};
+
+#[derive(Debug)]
+pub(crate) struct MacroRender<'a> {
+    ctx: RenderContext<'a>,
+    name: String,
+    macro_: hir::MacroDef,
+    docs: Option<Documentation>,
+    bra: &'static str,
+    ket: &'static str,
+}
+
+impl<'a> MacroRender<'a> {
+    pub(crate) fn new(
+        ctx: RenderContext<'a>,
+        name: String,
+        macro_: hir::MacroDef,
+    ) -> MacroRender<'a> {
+        let docs = macro_.docs(ctx.db());
+        let docs_str = docs.as_ref().map_or("", |s| s.as_str());
+        let (bra, ket) = guess_macro_braces(&name, docs_str);
+
+        MacroRender { ctx, name, macro_, docs, bra, ket }
+    }
+
+    pub(crate) fn render(&self) -> Option<CompletionItem> {
+        // FIXME: Currently proc-macro do not have ast-node,
+        // such that it does not have source
+        if self.macro_.is_proc_macro() {
+            return None;
+        }
+
+        let mut builder =
+            CompletionItem::new(CompletionKind::Reference, self.ctx.source_range(), &self.label())
+                .kind(CompletionItemKind::Macro)
+                .set_documentation(self.docs.clone())
+                .set_deprecated(self.ctx.is_deprecated(self.macro_))
+                .detail(self.detail());
+
+        let needs_bang = self.needs_bang();
+        builder = match self.ctx.snippet_cap() {
+            Some(cap) if needs_bang => {
+                let snippet = self.snippet();
+                let lookup = self.lookup();
+                builder.insert_snippet(cap, snippet).lookup_by(lookup)
+            }
+            None if needs_bang => builder.insert_text(self.banged_name()),
+            _ => {
+                mark::hit!(dont_insert_macro_call_parens_unncessary);
+                builder.insert_text(&self.name)
+            }
+        };
+
+        Some(builder.build())
+    }
+
+    fn needs_bang(&self) -> bool {
+        self.ctx.completion.use_item_syntax.is_none() && !self.ctx.completion.is_macro_call
+    }
+
+    fn label(&self) -> String {
+        format!("{}!{}…{}", self.name, self.bra, self.ket)
+    }
+
+    fn snippet(&self) -> String {
+        format!("{}!{}$0{}", self.name, self.bra, self.ket)
+    }
+
+    fn lookup(&self) -> String {
+        self.banged_name()
+    }
+
+    fn banged_name(&self) -> String {
+        format!("{}!", self.name)
+    }
+
+    fn detail(&self) -> String {
+        let ast_node = self.macro_.source(self.ctx.db()).value;
+        macro_label(&ast_node)
+    }
+}
+
+fn guess_macro_braces(macro_name: &str, docs: &str) -> (&'static str, &'static str) {
+    let mut votes = [0, 0, 0];
+    for (idx, s) in docs.match_indices(&macro_name) {
+        let (before, after) = (&docs[..idx], &docs[idx + s.len()..]);
+        // Ensure to match the full word
+        if after.starts_with('!')
+            && !before.ends_with(|c: char| c == '_' || c.is_ascii_alphanumeric())
+        {
+            // It may have spaces before the braces like `foo! {}`
+            match after[1..].chars().find(|&c| !c.is_whitespace()) {
+                Some('{') => votes[0] += 1,
+                Some('[') => votes[1] += 1,
+                Some('(') => votes[2] += 1,
+                _ => {}
+            }
+        }
+    }
+
+    // Insert a space before `{}`.
+    // We prefer the last one when some votes equal.
+    let (_vote, (bra, ket)) = votes
+        .iter()
+        .zip(&[(" {", "}"), ("[", "]"), ("(", ")")])
+        .max_by_key(|&(&vote, _)| vote)
+        .unwrap();
+    (*bra, *ket)
+}