[gcc/devel/rust/master] parser: Allow parsing of qualified type path as nested generic argument

[gcc/devel/rust/master] parser: Allow parsing of qualified type path as nested generic argument

[Thomas Schwinge]

https://gcc.gnu.org/g:57b64a64261ed1d1774af61a1e36eeac604abcde

commit 57b64a64261ed1d1774af61a1e36eeac604abcde
Author: Arthur Cohen <arthur.cohen@embecosm.com>
Date:   Thu Feb 16 13:53:22 2023 +0100

    parser: Allow parsing of qualified type path as nested generic argument
    
    Let's take the example of lexing `Option<<T as Iterator>::Item>` and look
    at the first few tokens. Originally, `Option<<T` was lexed as 3 tokens:
    
    * IDENTIFIER(Option)
    * LEFT_SHIFT
    * IDENTIFIER(T)
    
    The parser did not allow a list of generic arguments to start with a left
    shift, and rejected the above type. We are now splitting the left shift
    into two left angles, as this allows complex generic arguments and overall
    makes sense parsing wise. Thus, the above list becomes:
    
    * IDENTIFIER(Option)
    * LEFT_ANGLE
    * LEFT_ANGLE
    * IDENTIFIER(T)
    
    and `<T as Iterator>` is properly parsed as a qualified path.
    
    Fixes #1815
    Fixed #1809
    
    Addresses #1524
    
    gcc/rust/ChangeLog:
    
            * parse/rust-parse-impl.h (Parser::parse_path_generic_args): Split leading
            `LEFT_SHIFT` token into two `LEFT_ANGLE` tokens when parsing generic arguments.
            (Parser::parse_type_path_segment): Allow `LEFT_ANGLE` as starting token for
            parsing generic arguments.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/parse_associated_type_as_generic_arg.rs: New test.
            * rust/compile/parse_associated_type_as_generic_arg2.rs: New test.
            * rust/compile/path_as_generic_arg.rs: New test.
            * rust/compile/nested_generic.rs: New test.

Diff:
---
 gcc/rust/parse/rust-parse-impl.h                   |  4 ++++
 gcc/testsuite/rust/compile/nested_generic.rs       |  4 ++++
 .../parse_associated_type_as_generic_arg.rs        | 24 ++++++++++++++++++++++
 .../parse_associated_type_as_generic_arg2.rs       | 24 ++++++++++++++++++++++
 gcc/testsuite/rust/compile/path_as_generic_arg.rs  | 12 +++++++++++
 5 files changed, 68 insertions(+)

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 4c39284749d..3bf26bc6fdc 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -6383,6 +6383,9 @@ template <typename ManagedTokenSource>
 AST::GenericArgs
 Parser<ManagedTokenSource>::parse_path_generic_args ()
 {
+  if (lexer.peek_token ()->get_id () == LEFT_SHIFT)
+    lexer.split_current_token (LEFT_ANGLE, LEFT_ANGLE);
+
   if (!skip_token (LEFT_ANGLE))
     {
       // skip after somewhere?
@@ -6557,6 +6560,7 @@ Parser<ManagedTokenSource>::parse_type_path_segment ()
   const_TokenPtr t = lexer.peek_token ();
   switch (t->get_id ())
     {
+    case LEFT_SHIFT:
       case LEFT_ANGLE: {
 	// parse generic args
 	AST::GenericArgs generic_args = parse_path_generic_args ();
diff --git a/gcc/testsuite/rust/compile/nested_generic.rs b/gcc/testsuite/rust/compile/nested_generic.rs
new file mode 100644
index 00000000000..6c3109957f9
--- /dev/null
+++ b/gcc/testsuite/rust/compile/nested_generic.rs
@@ -0,0 +1,4 @@
+pub struct A<T>(T);
+pub struct B<T>(T);
+
+pub fn foo(_: A<B<i32>>) {}
diff --git a/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg.rs b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg.rs
new file mode 100644
index 00000000000..dc05c068359
--- /dev/null
+++ b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg.rs
@@ -0,0 +1,24 @@
+// { dg-additional-options "-fsyntax-only" }
+
+trait Foo {
+    type A;
+
+    fn foo();
+}
+
+struct S;
+
+impl Foo for S {
+    type A = i32;
+
+    fn foo() {}
+}
+
+enum Maybe<T> {
+    Something(T),
+    Nothing,
+}
+
+fn foo() -> Maybe<<S as Foo>::A> {
+    Maybe::Something(15)
+}
diff --git a/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg2.rs b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg2.rs
new file mode 100644
index 00000000000..9c518a03ca7
--- /dev/null
+++ b/gcc/testsuite/rust/compile/parse_associated_type_as_generic_arg2.rs
@@ -0,0 +1,24 @@
+// { dg-additional-options "-fsyntax-only" }
+
+trait Foo {
+    type A;
+
+    fn foo();
+}
+
+struct S;
+
+impl Foo for S {
+    type A = ();
+
+    fn foo() {}
+}
+
+enum Maybe<T> {
+    Something(T),
+    Nothing,
+}
+
+fn main() {
+    let a: Maybe<<S as Foo>::A> = Maybe::Something(());
+}
diff --git a/gcc/testsuite/rust/compile/path_as_generic_arg.rs b/gcc/testsuite/rust/compile/path_as_generic_arg.rs
new file mode 100644
index 00000000000..35b3160e9a8
--- /dev/null
+++ b/gcc/testsuite/rust/compile/path_as_generic_arg.rs
@@ -0,0 +1,12 @@
+pub enum Result<T, E> {
+    Ok(T),
+    Err(E),
+}
+
+pub mod module {
+    pub struct E;
+}
+
+pub fn foo() -> Result<(), module::E> {
+    Result::Err(module::E)
+}