Add macro segment completion

Example
---
```rust
macro_rules! foo {
    ($($x:$0)*) => ();
}
```

**Completion items**:

```text
ba block
ba expr
ba expr_2021
ba ident
ba item
ba lifetime
ba literal
ba meta
ba pat
ba pat_param
ba path
ba stmt
ba tt
ba ty
ba vis
```

crates/ide-completion/src/completions.rs

@@ -13,6 +13,7 @@ pub(crate) mod format_string;
 pub(crate) mod item_list;
 pub(crate) mod keyword;
 pub(crate) mod lifetime;
+pub(crate) mod macro_def;
 pub(crate) mod mod_;
 pub(crate) mod pattern;
 pub(crate) mod postfix;

crates/ide-completion/src/completions/macro_def.rs

@@ -0,0 +1,31 @@
+//! Completion for macro meta-variable segments
+
+use ide_db::SymbolKind;
+
+use crate::{CompletionItem, Completions, context::CompletionContext};
+
+pub(crate) fn complete_macro_segment(acc: &mut Completions, ctx: &CompletionContext<'_>) {
+    for &label in MACRO_SEGMENTS {
+        let item =
+            CompletionItem::new(SymbolKind::BuiltinAttr, ctx.source_range(), label, ctx.edition);
+        item.add_to(acc, ctx.db);
+    }
+}
+
+const MACRO_SEGMENTS: &[&str] = &[
+    "ident",
+    "block",
+    "stmt",
+    "expr",
+    "pat",
+    "ty",
+    "lifetime",
+    "literal",
+    "path",
+    "meta",
+    "tt",
+    "item",
+    "vis",
+    "expr_2021",
+    "pat_param",
+];

crates/ide-completion/src/context.rs

@@ -13,7 +13,7 @@ use hir::{
 };
 use ide_db::{
     FilePosition, FxHashMap, FxHashSet, RootDatabase, famous_defs::FamousDefs,
-    helpers::is_editable_crate,
+    helpers::is_editable_crate, syntax_helpers::node_ext::is_in_macro_matcher,
 };
 use itertools::Either;
 use syntax::{
@@ -389,6 +389,7 @@ pub(crate) enum CompletionAnalysis<'db> {
         fake_attribute_under_caret: Option<ast::Attr>,
         extern_crate: Option<ast::ExternCrate>,
     },
+    MacroSegment,
 }
 
 /// Information about the field or method access we are completing.
@@ -729,7 +730,7 @@ impl<'db> CompletionContext<'db> {
             let prev_token = original_token.prev_token()?;
 
             // only has a single colon
-            if prev_token.kind() != T![:] {
+            if prev_token.kind() != T![:] && !is_in_macro_matcher(&original_token) {
                 return None;
             }
 

crates/ide-completion/src/context/analysis.rs

@@ -5,7 +5,7 @@ use hir::{ExpandResult, InFile, Semantics, Type, TypeInfo, Variant};
 use ide_db::{
     RootDatabase, active_parameter::ActiveParameter, syntax_helpers::node_ext::find_loops,
 };
-use itertools::Either;
+use itertools::{Either, Itertools};
 use stdx::always;
 use syntax::{
     AstNode, AstToken, Direction, NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken,
@@ -510,6 +510,21 @@ fn analyze<'db>(
                     colon_prefix,
                     extern_crate: p.ancestors().find_map(ast::ExternCrate::cast),
                 }
+            } else if p.kind() == SyntaxKind::TOKEN_TREE
+                && p.ancestors().any(|it| ast::Macro::can_cast(it.kind()))
+            {
+                if let Some([_ident, colon, _name, dollar]) = fake_ident_token
+                    .siblings_with_tokens(Direction::Prev)
+                    .filter(|it| !it.kind().is_trivia())
+                    .take(4)
+                    .collect_array()
+                    && dollar.kind() == T![$]
+                    && colon.kind() == T![:]
+                {
+                    CompletionAnalysis::MacroSegment
+                } else {
+                    return None;
+                }
             } else {
                 return None;
             }

crates/ide-completion/src/lib.rs

@@ -263,6 +263,9 @@ pub fn completions(
                     extern_crate.as_ref(),
                 );
             }
+            CompletionAnalysis::MacroSegment => {
+                completions::macro_def::complete_macro_segment(acc, ctx);
+            }
             CompletionAnalysis::UnexpandedAttrTT { .. } | CompletionAnalysis::String { .. } => (),
         }
     }

crates/ide-completion/src/tests/special.rs

@@ -481,6 +481,226 @@ fn foo() {}
     );
 }
 
+#[test]
+fn completes_macro_segment() {
+    check(
+        r#"
+macro_rules! foo {
+    ($x:e$0) => ();
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check(
+        r#"
+macro_rules! foo {
+    ($x:$0) => ();
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check(
+        r#"
+macro_rules! foo {
+    ($($x:$0)*) => ();
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check(
+        r#"
+macro foo {
+    ($($x:$0)*) => ();
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check(
+        r#"
+macro foo($($x:$0)*) {
+    xxx;
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check_edit(
+        "expr",
+        r#"
+macro foo($($x:$0)*) {
+    xxx;
+}
+"#,
+        r#"
+macro foo($($x:expr)*) {
+    xxx;
+}
+"#,
+    );
+
+    check(
+        r#"
+macro_rules! foo {
+    ($fn : e$0) => ();
+}
+"#,
+        expect![[r#"
+            ba block
+            ba expr
+            ba expr_2021
+            ba ident
+            ba item
+            ba lifetime
+            ba literal
+            ba meta
+            ba pat
+            ba pat_param
+            ba path
+            ba stmt
+            ba tt
+            ba ty
+            ba vis
+        "#]],
+    );
+
+    check_edit(
+        "expr",
+        r#"
+macro foo($($x:ex$0)*) {
+    xxx;
+}
+"#,
+        r#"
+macro foo($($x:expr)*) {
+    xxx;
+}
+"#,
+    );
+}
+
+#[test]
+fn completes_in_macro_body() {
+    check(
+        r#"
+macro_rules! foo {
+    ($x:expr) => ($y:$0);
+}
+"#,
+        expect![[r#""#]],
+    );
+
+    check(
+        r#"
+macro_rules! foo {
+    ($x:expr) => ({$y:$0});
+}
+"#,
+        expect![[r#""#]],
+    );
+
+    check(
+        r#"
+macro foo {
+    ($x:expr) => ($y:$0);
+}
+"#,
+        expect![[r#""#]],
+    );
+
+    check(
+        r#"
+macro foo($x:expr) {
+    $y:$0
+}
+"#,
+        expect![[r#""#]],
+    );
+}
+
 #[test]
 fn function_mod_share_name() {
     check_no_kw(
@@ -942,6 +1162,15 @@ fn foo { crate::$0 }
     check_with_trigger_character(
         r#"
 fn foo { crate:$0 }
+"#,
+        Some(':'),
+        expect![""],
+    );
+
+    check_with_trigger_character(
+        r#"
+macro_rules! bar { ($($x:tt)*) => ($($x)*); }
+fn foo { bar!(crate:$0) }
 "#,
         Some(':'),
         expect![""],

crates/ide-db/src/syntax_helpers/node_ext.rs

@@ -5,8 +5,10 @@ use itertools::Itertools;
 use parser::T;
 use span::Edition;
 use syntax::{
-    AstNode, AstToken, Preorder, RustLanguage, WalkEvent,
+    AstNode, AstToken, Direction, Preorder, RustLanguage, SyntaxToken, WalkEvent,
+    algo::non_trivia_sibling,
     ast::{self, HasLoopBody, MacroCall, PathSegmentKind, VisibilityKind},
+    syntax_editor::Element,
 };
 
 pub fn expr_as_name_ref(expr: &ast::Expr) -> Option<ast::NameRef> {
@@ -542,3 +544,33 @@ pub fn macro_call_for_string_token(string: &ast::String) -> Option<MacroCall> {
     let macro_call = string.syntax().parent_ancestors().find_map(ast::MacroCall::cast)?;
     Some(macro_call)
 }
+
+pub fn is_in_macro_matcher(token: &SyntaxToken) -> bool {
+    let Some(macro_def) = token.parent_ancestors().find_map(ast::Macro::cast) else {
+        return false;
+    };
+    let range = token.text_range();
+    let Some(body) = (match macro_def {
+        ast::Macro::MacroDef(macro_def) => {
+            if let Some(args) = macro_def.args() {
+                return args.syntax().text_range().contains_range(range);
+            }
+            macro_def.body()
+        }
+        ast::Macro::MacroRules(macro_rules) => macro_rules.token_tree(),
+    }) else {
+        return false;
+    };
+    if !body.syntax().text_range().contains_range(range) {
+        return false;
+    }
+    body.token_trees_and_tokens().filter_map(|tt| tt.into_node()).any(|tt| {
+        let Some(next) = non_trivia_sibling(tt.syntax().syntax_element(), Direction::Next) else {
+            return false;
+        };
+        let Some(next_next) = next.next_sibling_or_token() else { return false };
+        next.kind() == T![=]
+            && next_next.kind() == T![>]
+            && tt.syntax().text_range().contains_range(range)
+    })
+}