macros: add `#[no_arg]` to skip `set_arg` call

A call to `set_arg` is generated for every field of a
`SessionDiagnostic` struct without attributes, but not all types support
being an argument, so `#[no_arg]` is introduced to skip these fields.

Signed-off-by: David Wood <david.wood@huawei.com>

2 files changed, 33 insertions, 1 deletions

diff --git a/src/test/ui-fulldeps/session-derive-errors.rs b/src/test/ui-fulldeps/session-derive-errors.rs
index 422f3894991..96d78c2d00e 100644
--- a/src/test/ui-fulldeps/session-derive-errors.rs
+++ b/src/test/ui-fulldeps/session-derive-errors.rs
@@ -311,3 +311,23 @@ struct ErrorWithLifetime<'a> {
     span: Span,
     name: &'a str,
 }
+
+#[derive(SessionDiagnostic)]
+//~^ ERROR no method named `into_diagnostic_arg` found for struct `Hello` in the current scope
+#[error(code = "E0123", slug = "foo")]
+struct ArgFieldWithoutSkip {
+    #[primary_span]
+    span: Span,
+    other: Hello,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(code = "E0123", slug = "foo")]
+struct ArgFieldWithSkip {
+    #[primary_span]
+    span: Span,
+    // `Hello` does not implement `IntoDiagnosticArg` so this would result in an error if
+    // not for `#[skip_arg]`.
+    #[skip_arg]
+    other: Hello,
+}
diff --git a/src/test/ui-fulldeps/session-derive-errors.stderr b/src/test/ui-fulldeps/session-derive-errors.stderr
index 78ed255523f..21bf8e060ba 100644
--- a/src/test/ui-fulldeps/session-derive-errors.stderr
+++ b/src/test/ui-fulldeps/session-derive-errors.stderr
@@ -274,5 +274,17 @@ error: cannot find attribute `nonsense` in this scope
 LL |     #[nonsense]
    |       ^^^^^^^^
 
-error: aborting due to 34 previous errors
+error[E0599]: no method named `into_diagnostic_arg` found for struct `Hello` in the current scope
+  --> $DIR/session-derive-errors.rs:315:10
+   |
+LL | struct Hello {}
+   | ------------ method `into_diagnostic_arg` not found for this
+...
+LL | #[derive(SessionDiagnostic)]
+   |          ^^^^^^^^^^^^^^^^^ method not found in `Hello`
+   |
+   = note: this error originates in the derive macro `SessionDiagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 35 previous errors
 
+For more information about this error, try `rustc --explain E0599`.