1 files changed, 132 insertions, 0 deletions

diff --git a/crates/parser/src/grammar/items/use_item.rs b/crates/parser/src/grammar/items/use_item.rs
new file mode 100644
index 000000000..8e836a77e
--- /dev/null
+++ b/crates/parser/src/grammar/items/use_item.rs
@@ -0,0 +1,132 @@
+//! FIXME: write short doc here
+
+use super::*;
+
+pub(super) fn use_item(p: &mut Parser, m: Marker) {
+    assert!(p.at(T![use]));
+    p.bump(T![use]);
+    use_tree(p, true);
+    p.expect(T![;]);
+    m.complete(p, USE);
+}
+
+/// Parse a use 'tree', such as `some::path` in `use some::path;`
+/// Note that this is called both by `use_item` and `use_tree_list`,
+/// so handles both `some::path::{inner::path}` and `inner::path` in
+/// `use some::path::{inner::path};`
+fn use_tree(p: &mut Parser, top_level: bool) {
+    let m = p.start();
+    match p.current() {
+        // Finish the use_tree for cases of e.g.
+        // `use some::path::{self, *};` or `use *;`
+        // This does not handle cases such as `use some::path::*`
+        // N.B. in Rust 2015 `use *;` imports all from crate root
+        // however in Rust 2018 `use *;` errors: ('cannot glob-import all possible crates')
+        // FIXME: Add this error (if not out of scope)
+
+        // test use_star
+        // use *;
+        // use ::*;
+        // use some::path::{*};
+        // use some::path::{::*};
+        T![*] => p.bump(T![*]),
+        T![:] if p.at(T![::]) && p.nth(2) == T![*] => {
+            // Parse `use ::*;`, which imports all from the crate root in Rust 2015
+            // This is invalid inside a use_tree_list, (e.g. `use some::path::{::*}`)
+            // but still parses and errors later: ('crate root in paths can only be used in start position')
+            // FIXME: Add this error (if not out of scope)
+            // In Rust 2018, it is always invalid (see above)
+            p.bump(T![::]);
+            p.bump(T![*]);
+        }
+        // Open a use tree list
+        // Handles cases such as `use {some::path};` or `{inner::path}` in
+        // `use some::path::{{inner::path}, other::path}`
+
+        // test use_tree_list
+        // use {crate::path::from::root, or::path::from::crate_name}; // Rust 2018 (with a crate named `or`)
+        // use {path::from::root}; // Rust 2015
+        // use ::{some::arbritrary::path}; // Rust 2015
+        // use ::{{{root::export}}}; // Nonsensical but perfectly legal nesting
+        T!['{'] => {
+            use_tree_list(p);
+        }
+        T![:] if p.at(T![::]) && p.nth(2) == T!['{'] => {
+            p.bump(T![::]);
+            use_tree_list(p);
+        }
+        // Parse a 'standard' path.
+        // Also handles aliases (e.g. `use something as something_else`)
+
+        // test use_path
+        // use ::crate_name; // Rust 2018 - All flavours
+        // use crate_name; // Rust 2018 - Anchored paths
+        // use item_in_scope_or_crate_name; // Rust 2018 - Uniform Paths
+        //
+        // use self::module::Item;
+        // use crate::Item;
+        // use self::some::Struct;
+        // use crate_name::some_item;
+        _ if paths::is_use_path_start(p) => {
+            paths::use_path(p);
+            match p.current() {
+                T![as] => {
+                    // test use_alias
+                    // use some::path as some_name;
+                    // use some::{
+                    //  other::path as some_other_name,
+                    //  different::path as different_name,
+                    //  yet::another::path,
+                    //  running::out::of::synonyms::for_::different::*
+                    // };
+                    // use Trait as _;
+                    opt_alias(p);
+                }
+                T![:] if p.at(T![::]) => {
+                    p.bump(T![::]);
+                    match p.current() {
+                        T![*] => {
+                            p.bump(T![*]);
+                        }
+                        // test use_tree_list_after_path
+                        // use crate::{Item};
+                        // use self::{Item};
+                        T!['{'] => use_tree_list(p),
+                        _ => {
+                            // is this unreachable?
+                            p.error("expected `{` or `*`");
+                        }
+                    }
+                }
+                _ => (),
+            }
+        }
+        _ => {
+            m.abandon(p);
+            let msg = "expected one of `*`, `::`, `{`, `self`, `super` or an identifier";
+            if top_level {
+                p.err_recover(msg, ITEM_RECOVERY_SET);
+            } else {
+                // if we are parsing a nested tree, we have to eat a token to
+                // main balanced `{}`
+                p.err_and_bump(msg);
+            }
+            return;
+        }
+    }
+    m.complete(p, USE_TREE);
+}
+
+pub(crate) fn use_tree_list(p: &mut Parser) {
+    assert!(p.at(T!['{']));
+    let m = p.start();
+    p.bump(T!['{']);
+    while !p.at(EOF) && !p.at(T!['}']) {
+        use_tree(p, false);
+        if !p.at(T!['}']) {
+            p.expect(T![,]);
+        }
+    }
+    p.expect(T!['}']);
+    m.complete(p, USE_TREE_LIST);
+}