Add completions for patterns

1 files changed, 128 insertions, 0 deletions

diff --git a/crates/completion/src/render/pattern.rs b/crates/completion/src/render/pattern.rs
new file mode 100644
index 000000000..e20b0027b
--- /dev/null
+++ b/crates/completion/src/render/pattern.rs
@@ -0,0 +1,128 @@
+//! Renderer for patterns.
+
+use hir::{db::HirDatabase, HasVisibility, Name, StructKind};
+use itertools::Itertools;
+
+use crate::{item::CompletionKind, render::RenderContext, CompletionItem, CompletionItemKind};
+
+pub(crate) fn render_struct_pat<'a>(
+    ctx: RenderContext<'a>,
+    strukt: hir::Struct,
+    local_name: Option<Name>,
+) -> Option<CompletionItem> {
+    let _p = profile::span("render_struct_pat");
+
+    let module = ctx.completion.scope.module()?;
+    let fields = strukt.fields(ctx.db());
+    let n_fields = fields.len();
+    let fields = fields
+        .into_iter()
+        .filter(|field| field.is_visible_from(ctx.db(), module))
+        .collect::<Vec<_>>();
+
+    if fields.is_empty() {
+        // Matching a struct without matching its fields is pointless, unlike matching a Variant without its fields
+        return None;
+    }
+    let fields_omitted = n_fields - fields.len() > 0;
+
+    let name = local_name.unwrap_or_else(|| strukt.name(ctx.db())).to_string();
+    let mut pat = match strukt.kind(ctx.db()) {
+        StructKind::Tuple if ctx.snippet_cap().is_some() => {
+            render_tuple_as_pat(&fields, &name, fields_omitted)
+        }
+        StructKind::Record => render_record_as_pat(ctx.db(), &fields, &name, fields_omitted),
+        _ => return None,
+    };
+
+    if ctx.completion.is_param {
+        pat.push(':');
+        pat.push(' ');
+        pat.push_str(&name);
+    }
+    if ctx.snippet_cap().is_some() {
+        pat.push_str("$0");
+    }
+
+    let mut completion = CompletionItem::new(CompletionKind::Snippet, ctx.source_range(), name)
+        .kind(CompletionItemKind::Binding)
+        .set_documentation(ctx.docs(strukt))
+        .set_deprecated(ctx.is_deprecated(strukt))
+        .detail(&pat);
+    if let Some(snippet_cap) = ctx.snippet_cap() {
+        completion = completion.insert_snippet(snippet_cap, pat);
+    } else {
+        completion = completion.insert_text(pat);
+    }
+    Some(completion.build())
+}
+
+pub(crate) fn render_variant_pat<'a>(
+    ctx: RenderContext<'a>,
+    variant: hir::Variant,
+    local_name: Option<Name>,
+) -> Option<CompletionItem> {
+    let _p = profile::span("render_variant_pat");
+
+    let module = ctx.completion.scope.module()?;
+    let fields = variant.fields(ctx.db());
+    let n_fields = fields.len();
+    let fields = fields
+        .into_iter()
+        .filter(|field| field.is_visible_from(ctx.db(), module))
+        .collect::<Vec<_>>();
+
+    let fields_omitted = n_fields - fields.len() > 0;
+
+    let name = local_name.unwrap_or_else(|| variant.name(ctx.db())).to_string();
+    let mut pat = match variant.kind(ctx.db()) {
+        StructKind::Tuple if ctx.snippet_cap().is_some() => {
+            render_tuple_as_pat(&fields, &name, fields_omitted)
+        }
+        StructKind::Record => render_record_as_pat(ctx.db(), &fields, &name, fields_omitted),
+        _ => return None,
+    };
+
+    if ctx.completion.is_param {
+        pat.push(':');
+        pat.push(' ');
+        pat.push_str(&name);
+    }
+    if ctx.snippet_cap().is_some() {
+        pat.push_str("$0");
+    }
+    let mut completion = CompletionItem::new(CompletionKind::Snippet, ctx.source_range(), name)
+        .kind(CompletionItemKind::Binding)
+        .set_documentation(ctx.docs(variant))
+        .set_deprecated(ctx.is_deprecated(variant))
+        .detail(&pat);
+    if let Some(snippet_cap) = ctx.snippet_cap() {
+        completion = completion.insert_snippet(snippet_cap, pat);
+    } else {
+        completion = completion.insert_text(pat);
+    }
+    Some(completion.build())
+}
+
+fn render_record_as_pat(
+    db: &dyn HirDatabase,
+    fields: &[hir::Field],
+    name: &str,
+    fields_omitted: bool,
+) -> String {
+    format!(
+        "{name} {{ {}{} }}",
+        fields.into_iter().map(|field| field.name(db)).format(", "),
+        if fields_omitted { ", .." } else { "" },
+        name = name
+    )
+}
+
+fn render_tuple_as_pat(fields: &[hir::Field], name: &str, fields_omitted: bool) -> String {
+    format!(
+        "{name}({}{})",
+        fields.into_iter().enumerate().map(|(idx, _)| format!("${}", idx + 1)).format(", "),
+        if fields_omitted { ", .." } else { "" },
+        name = name
+    )
+}