Auto merge of #70261 - Centril:angle-args-partition, r=varkor

Move arg/constraint partition check to validation & improve recovery

- In the first commit, we move the check rejecting e.g., `<'a, Item = u8, String>` from the parser into AST validation.
- We then use this to improve the code for parsing generic arguments.
- And we add recovery for e.g., `<Item = >` (missing), `<Item = 42>` (constant), and `<Item = 'a>` (lifetime).

This is also preparatory work for supporting https://github.com/rust-lang/rust/issues/70256.

r? @varkor

9 files changed, 82 insertions, 5 deletions

diff --git a/src/test/ui/parser/constraints-before-generic-args-syntactic-pass.rs b/src/test/ui/parser/constraints-before-generic-args-syntactic-pass.rs
new file mode 100644
index 00000000000..afbd13e6fd9
--- /dev/null
+++ b/src/test/ui/parser/constraints-before-generic-args-syntactic-pass.rs
@@ -0,0 +1,9 @@
+// check-pass
+
+#[cfg(FALSE)]
+fn syntax() {
+    foo::<T = u8, T: Ord, String>();
+    foo::<T = u8, 'a, T: Ord>();
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-32214.rs b/src/test/ui/parser/issue-32214.rs
index 82f7ce62b94..1379eeb58e6 100644
--- a/src/test/ui/parser/issue-32214.rs
+++ b/src/test/ui/parser/issue-32214.rs
@@ -1,6 +1,6 @@
 trait Trait<T> { type Item; }
 
 pub fn test<W, I: Trait<Item=(), W> >() {}
-//~^ ERROR associated type bindings must be declared after generic parameters
+//~^ ERROR generic arguments must come before the first constraint
 
 fn main() { }
diff --git a/src/test/ui/parser/issue-32214.stderr b/src/test/ui/parser/issue-32214.stderr
index 08b230a14f5..742f4fdc38b 100644
--- a/src/test/ui/parser/issue-32214.stderr
+++ b/src/test/ui/parser/issue-32214.stderr
@@ -1,10 +1,10 @@
-error: associated type bindings must be declared after generic parameters
-  --> $DIR/issue-32214.rs:3:25
+error: generic arguments must come before the first constraint
+  --> $DIR/issue-32214.rs:3:34
    |
 LL | pub fn test<W, I: Trait<Item=(), W> >() {}
-   |                         -------^^^
+   |                         -------  ^ generic argument
    |                         |
-   |                         this associated type binding should be moved after the generic parameters
+   |                         the first constraint is provided here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/parser/recover-assoc-const-constraint.rs b/src/test/ui/parser/recover-assoc-const-constraint.rs
new file mode 100644
index 00000000000..06be3cdcc1a
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-const-constraint.rs
@@ -0,0 +1,7 @@
+#[cfg(FALSE)]
+fn syntax() {
+    bar::<Item = 42>(); //~ ERROR cannot constrain an associated constant to a value
+    bar::<Item = { 42 }>(); //~ ERROR cannot constrain an associated constant to a value
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/recover-assoc-const-constraint.stderr b/src/test/ui/parser/recover-assoc-const-constraint.stderr
new file mode 100644
index 00000000000..c6733b33faa
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-const-constraint.stderr
@@ -0,0 +1,20 @@
+error: cannot constrain an associated constant to a value
+  --> $DIR/recover-assoc-const-constraint.rs:3:11
+   |
+LL |     bar::<Item = 42>();
+   |           ----^^^--
+   |           |      |
+   |           |      ...cannot be constrained to this value
+   |           this associated constant...
+
+error: cannot constrain an associated constant to a value
+  --> $DIR/recover-assoc-const-constraint.rs:4:11
+   |
+LL |     bar::<Item = { 42 }>();
+   |           ----^^^------
+   |           |      |
+   |           |      ...cannot be constrained to this value
+   |           this associated constant...
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/parser/recover-assoc-eq-missing-term.rs b/src/test/ui/parser/recover-assoc-eq-missing-term.rs
new file mode 100644
index 00000000000..4b42c44dc64
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-eq-missing-term.rs
@@ -0,0 +1,6 @@
+#[cfg(FALSE)]
+fn syntax() {
+    bar::<Item =   >(); //~ ERROR missing type to the right of `=`
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/recover-assoc-eq-missing-term.stderr b/src/test/ui/parser/recover-assoc-eq-missing-term.stderr
new file mode 100644
index 00000000000..6e41e139220
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-eq-missing-term.stderr
@@ -0,0 +1,17 @@
+error: missing type to the right of `=`
+  --> $DIR/recover-assoc-eq-missing-term.rs:3:17
+   |
+LL |     bar::<Item =   >();
+   |                 ^^^
+   |
+help: to constrain the associated type, add a type after `=`
+   |
+LL |     bar::<Item = TheType>();
+   |                  ^^^^^^^
+help: remove the `=` if `Item` is a type
+   |
+LL |     bar::<Item >();
+   |               --
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/parser/recover-assoc-lifetime-constraint.rs b/src/test/ui/parser/recover-assoc-lifetime-constraint.rs
new file mode 100644
index 00000000000..558fcdfe177
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-lifetime-constraint.rs
@@ -0,0 +1,6 @@
+#[cfg(FALSE)]
+fn syntax() {
+    bar::<Item = 'a>(); //~ ERROR associated lifetimes are not supported
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/recover-assoc-lifetime-constraint.stderr b/src/test/ui/parser/recover-assoc-lifetime-constraint.stderr
new file mode 100644
index 00000000000..79437533d7c
--- /dev/null
+++ b/src/test/ui/parser/recover-assoc-lifetime-constraint.stderr
@@ -0,0 +1,12 @@
+error: associated lifetimes are not supported
+  --> $DIR/recover-assoc-lifetime-constraint.rs:3:11
+   |
+LL |     bar::<Item = 'a>();
+   |           ^^^^^^^--
+   |                  |
+   |                  the lifetime is given here
+   |
+   = help: if you meant to specify a trait object, write `dyn Trait + 'lifetime`
+
+error: aborting due to previous error
+