Check target of module/assembly level suppressions (#2129)

* Check that global level suppressions do not specify any target

* Run lint

* Update test/Mono.Linker.Tests.Cases/Warnings/WarningSuppression/SuppressWarningsInModule.cs

Co-authored-by: Sven Boemer <sbomer@gmail.com>

* Add code snippet with an example of 2108.

* PR feedback
Add tests

* Lint

* Don't silently suppress warnings on module if scope is missing and a target was used.

Co-authored-by: Sven Boemer <sbomer@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/docs/error-codes.md b/docs/error-codes.md
index 2ef1b68ff..115b3c243 100644
--- a/docs/error-codes.md
+++ b/docs/error-codes.md
@@ -1683,6 +1683,29 @@ class Test
   }
   ```
 
+#### `IL2108`: Invalid scope 'scope' used in 'UnconditionalSuppressMessageAttribute' on module 'module' with target 'target'.
+
+The only scopes supported on global unconditional suppressions are 'module', 'type' and 'member'. If the scope and target arguments are null or missing on a global suppression,
+it is assumed that the suppression is put on the module. Global unconditional suppressions using invalid scopes are ignored.
+
+```C#
+// Invalid scope 'method' used in 'UnconditionalSuppressMessageAttribute' on module 'Warning' with target 'MyTarget'.
+[module: UnconditionalSuppressMessage ("Test suppression with invalid scope", "IL2026", Scope = "method", Target = "MyTarget")]
+
+class Warning
+{
+   static void Main(string[] args)
+   {
+      Foo();
+   }
+
+   [RequiresUnreferencedCode("Warn when Foo() is called")]
+   static void Foo()
+   {
+   }
+}
+```
+
 ## Single-File Warning Codes
 
 #### `IL3000`: 'member' always returns an empty string for assemblies embedded in a single-file app. If the path to the app directory is needed, consider calling 'System.AppContext.BaseDirectory'