[x-lint] add a stub for project linters

Closes: diem#3364
Approved by: bmwill

devtools/x-lint/src/lib.rs

@@ -199,7 +199,7 @@ pub mod prelude {
     pub use super::{
         content::{ContentContext, ContentLinter},
         file::FileContext,
-        project::ProjectContext,
+        project::{ProjectContext, ProjectLinter},
         LintFormatter, LintKind, LintLevel, LintMessage, LintSource, Linter, Result, RunStatus,
         SkipReason, SystemError,
     };

devtools/x-lint/src/project.rs

@@ -1,9 +1,22 @@
 // Copyright (c) The Libra Core Contributors
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::{LintContext, LintKind};
+use crate::prelude::*;
+use crate::LintContext;
 use std::path::{Path, PathBuf};
 
+/// Represents a linter that checks some property for the overall project.
+///
+/// Linters that implement `ProjectLinter` will run once for the whole project.
+pub trait ProjectLinter: Linter {
+    /// Executes the lint against the given project context.
+    fn run<'l>(
+        &self,
+        ctx: &ProjectContext<'l>,
+        out: &mut LintFormatter<'l, '_>,
+    ) -> Result<RunStatus<'l>>;
+}
+
 /// Overall linter context for a project.
 #[derive(Copy, Clone, Debug)]
 pub struct ProjectContext<'l> {