Metadata V15: Expose pallet documentation (#13452)

* frame/proc: Helpers to parse pallet documentation attributes

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/proc: Expand pallet with runtime metadata documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/dispatch: Implement doc function getter for dispatch

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/tests: Check exposed runtime metadata documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/tests: Add UI tests for `pallet_doc` attribute

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/proc: Document pallet_doc attribute

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Use `derive_syn_parse`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame/support/procedural/src/lib.rs

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* frame/support: Improve documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: parity-processbot <>
Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

substrate/frame/support/test/tests/pallet_ui/pallet_doc_arg_non_path.rs

@@ -0,0 +1,16 @@
+#[frame_support::pallet]
+// Must receive a string literal pointing to a path
+#[pallet_doc(X)]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config
+	where
+		<Self as frame_system::Config>::Index: From<u128>,
+	{
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+}
+
+fn main() {}

substrate/frame/support/test/tests/pallet_ui/pallet_doc_arg_non_path.stderr

@@ -0,0 +1,5 @@
+error: The `pallet_doc` received an unsupported argument. Supported format: `pallet_doc(PATH)`
+ --> tests/pallet_ui/pallet_doc_arg_non_path.rs:3:1
+  |
+3 | #[pallet_doc(X)]
+  | ^

substrate/frame/support/test/tests/pallet_ui/pallet_doc_empty.rs

@@ -0,0 +1,16 @@
+#[frame_support::pallet]
+// Expected one argument for the doc path.
+#[pallet_doc]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config
+	where
+		<Self as frame_system::Config>::Index: From<u128>,
+	{
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+}
+
+fn main() {}

substrate/frame/support/test/tests/pallet_ui/pallet_doc_empty.stderr

@@ -0,0 +1,5 @@
+error: The `pallet_doc` attribute must receive arguments as a list. Supported format: `pallet_doc(PATH)`
+ --> tests/pallet_ui/pallet_doc_empty.rs:3:1
+  |
+3 | #[pallet_doc]
+  | ^

substrate/frame/support/test/tests/pallet_ui/pallet_doc_invalid_arg.rs

@@ -0,0 +1,16 @@
+#[frame_support::pallet]
+// Argument expected as list, not named value.
+#[pallet_doc = "invalid"]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config
+	where
+		<Self as frame_system::Config>::Index: From<u128>,
+	{
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+}
+
+fn main() {}

substrate/frame/support/test/tests/pallet_ui/pallet_doc_invalid_arg.stderr

@@ -0,0 +1,5 @@
+error: The `pallet_doc` attribute must receive arguments as a list. Supported format: `pallet_doc(PATH)`
+ --> tests/pallet_ui/pallet_doc_invalid_arg.rs:3:1
+  |
+3 | #[pallet_doc = "invalid"]
+  | ^

substrate/frame/support/test/tests/pallet_ui/pallet_doc_multiple_args.rs

@@ -0,0 +1,16 @@
+#[frame_support::pallet]
+// Supports only one argument.
+#[pallet_doc("A", "B")]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config
+	where
+		<Self as frame_system::Config>::Index: From<u128>,
+	{
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+}
+
+fn main() {}

substrate/frame/support/test/tests/pallet_ui/pallet_doc_multiple_args.stderr

@@ -0,0 +1,5 @@
+error: The `pallet_doc` attribute must receive only one argument. Supported format: `pallet_doc(PATH)`
+ --> tests/pallet_ui/pallet_doc_multiple_args.rs:3:1
+  |
+3 | #[pallet_doc("A", "B")]
+  | ^