diff --git a/src/doc/rustc-dev-guide/src/tests/ui.md b/src/doc/rustc-dev-guide/src/tests/ui.md
index b31c861c947a0..5a2a06261846c 100644
--- a/src/doc/rustc-dev-guide/src/tests/ui.md
+++ b/src/doc/rustc-dev-guide/src/tests/ui.md
@@ -218,6 +218,9 @@ fn meow(_: [u8]) {}
 //~| ERROR anonymous parameters
 ```
 
+A question mark after the error kind (`//~ ERROR?`) means that the annotation error is not actually
+required to be produced by the compiler, this is useful for target-dependent errors.
+
 The space character between `//~` (or other variants) and the subsequent text is
 negligible (i.e. there is no semantic difference between `//~ ERROR` and
 `//~ERROR` although the former is more common in the codebase).
@@ -335,7 +338,9 @@ Use of `error-pattern` is not recommended in general.
 For strict testing of compile time output, try to use the line annotations `//~` as much as
 possible, including `//~?` annotations for diagnostics without spans.
 
-If the compile time output is target dependent or too verbose, use directive
+If the compile time output is target dependent, use optional annotations `//~ ERROR?`.
+
+If the compile time output is too verbose, use directive
 `//@ dont-require-annotations: <diagnostic-kind>` to make the line annotation checking
 non-exhaustive.
 Some of the compiler messages can stay uncovered by annotations in this mode.
diff --git a/src/tools/compiletest/src/errors.rs b/src/tools/compiletest/src/errors.rs
index a45f39b036cc9..1cb7243069382 100644
--- a/src/tools/compiletest/src/errors.rs
+++ b/src/tools/compiletest/src/errors.rs
@@ -65,9 +65,10 @@ pub struct Error {
     /// What kind of message we expect (e.g., warning, error, suggestion).
     pub kind: ErrorKind,
     pub msg: String,
-    /// For some `Error`s, like secondary lines of multi-line diagnostics, line annotations
-    /// are not mandatory, even if they would otherwise be mandatory for primary errors.
-    /// Only makes sense for "actual" errors, not for "expected" errors.
+    /// For `Error`s from the compiler, like secondary lines of multi-line diagnostics, line
+    /// annotations are not mandatory, even if they would otherwise be mandatory for primary errors.
+    /// For `Error`s from annotations this can be false if the annotation doesn't require to
+    /// annotate an actual error (useful for target-dependent errors).
     pub require_annotation: bool,
 }
 
@@ -167,7 +168,9 @@ fn parse_expected(
         rest.split_once(|c: char| c != '_' && !c.is_ascii_alphabetic()).unwrap_or((rest, ""));
     let kind = ErrorKind::from_user_str(kind_str);
     let untrimmed_msg = &rest[kind_str.len()..];
-    let msg = untrimmed_msg.strip_prefix(':').unwrap_or(untrimmed_msg).trim().to_owned();
+    let require_annotation = !untrimmed_msg.starts_with('?');
+    let msg = untrimmed_msg.strip_prefix('?').unwrap_or(untrimmed_msg);
+    let msg = msg.strip_prefix(':').unwrap_or(msg).trim().to_owned();
 
     let line_num_adjust = &captures["adjust"];
     let (follow_prev, line_num) = if line_num_adjust == "|" {
@@ -188,7 +191,7 @@ fn parse_expected(
         kind,
         msg
     );
-    Some((follow_prev, Error { line_num, kind, msg, require_annotation: true }))
+    Some((follow_prev, Error { line_num, kind, msg, require_annotation }))
 }
 
 #[cfg(test)]
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 97cb82c9e363a..dada828aa8cd0 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -753,7 +753,7 @@ impl<'test> TestCx<'test> {
         let mut not_found = Vec::new();
         // anything not yet found is a problem
         for (index, expected_error) in expected_errors.iter().enumerate() {
-            if !found[index] {
+            if expected_error.require_annotation && !found[index] {
                 self.error(&format!(
                     "{}:{}: expected {} not found: {}",
                     file_name,
diff --git a/tests/ui/cfg/cfg_false_no_std-2.rs b/tests/ui/cfg/cfg_false_no_std-2.rs
index 18b2c699fd7a5..32e77889b003b 100644
--- a/tests/ui/cfg/cfg_false_no_std-2.rs
+++ b/tests/ui/cfg/cfg_false_no_std-2.rs
@@ -1,6 +1,5 @@
 // Error, the linked empty library is `no_std` and doesn't provide a panic handler.
 
-//@ dont-require-annotations: ERROR
 //@ dont-check-compiler-stderr
 //@ aux-build: cfg_false_lib_no_std_before.rs
 
@@ -11,6 +10,4 @@ extern crate cfg_false_lib_no_std_before as _;
 fn main() {}
 
 //~? ERROR `#[panic_handler]` function required, but not found
-// FIXME: This error is target-dependent, could be served by some "optional error" annotation
-// instead of `dont-require-annotations`.
-//FIXME~? ERROR unwinding panics are not supported without std
+//~? ERROR? unwinding panics are not supported without std
diff --git a/tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.rs b/tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.rs
index b79b5ff6fdb1a..b2a07cd07c2c8 100644
--- a/tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.rs
+++ b/tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.rs
@@ -1,12 +1,11 @@
-//FIXME~ ERROR values of the type `[u8; usize::MAX]` are too big for the target architecture
+//~ ERROR? values of the type `[u8; usize::MAX]` are too big for the target architecture
 // Make sure the compiler does not ICE when trying to generate the debuginfo name of a type that
 // causes a layout error.
 // This version of the test already ICE'd before the commit that introduce the ICE described in
 // https://github.com/rust-lang/rust/issues/94961.
 
-//@ compile-flags:-C debuginfo=2 --error-format=human
+//@ compile-flags:-C debuginfo=2
 //@ build-fail
-//@ error-pattern: values of the type `[u8; usize::MAX]` are too big for the target architecture
 
 #![crate_type = "rlib"]
 
@@ -18,5 +17,5 @@ pub fn foo() -> usize {
     std::mem::size_of::<Foo<u8>>()
 }
 
-// FIXME: the error is reported on different lines on different targets
-//FIXME~? ERROR values of the type `[u8; usize::MAX]` are too big for the target architecture
+// The error is reported on different lines on different targets
+//~? ERROR? values of the type `[u8; usize::MAX]` are too big for the target architecture
diff --git a/tests/ui/panic-runtime/two-panic-runtimes.rs b/tests/ui/panic-runtime/two-panic-runtimes.rs
index 80591edd10771..3b4b813bbbd03 100644
--- a/tests/ui/panic-runtime/two-panic-runtimes.rs
+++ b/tests/ui/panic-runtime/two-panic-runtimes.rs
@@ -1,6 +1,4 @@
-// ignore-tidy-linelength
 //@ build-fail
-//@ dont-require-annotations: ERROR
 //@ dont-check-compiler-stderr
 //@ aux-build:panic-runtime-unwind.rs
 //@ aux-build:panic-runtime-unwind2.rs
@@ -16,7 +14,5 @@ extern crate panic_runtime_lang_items;
 fn main() {}
 
 //~? ERROR cannot link together two panic runtimes: panic_runtime_unwind and panic_runtime_unwind2
-// FIXME: These errors are target-dependent, could be served by some "optional error" annotation
-// instead of `dont-require-annotations`.
-//FIXME~? ERROR the linked panic runtime `panic_runtime_unwind2` is not compiled with this crate's panic strategy `abort`
-//FIXME~? ERROR the crate `panic_runtime_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`
+//~? ERROR? the linked panic runtime `panic_runtime_unwind2` is not compiled with this crate's panic strategy `abort`
+//~? ERROR? the crate `panic_runtime_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`
diff --git a/tests/ui/panic-runtime/want-abort-got-unwind.rs b/tests/ui/panic-runtime/want-abort-got-unwind.rs
index 42cdf8bc6626b..020243207ea03 100644
--- a/tests/ui/panic-runtime/want-abort-got-unwind.rs
+++ b/tests/ui/panic-runtime/want-abort-got-unwind.rs
@@ -1,6 +1,4 @@
-// ignore-tidy-linelength
 //@ build-fail
-//@ dont-require-annotations: ERROR
 //@ dont-check-compiler-stderr
 //@ aux-build:panic-runtime-unwind.rs
 //@ compile-flags:-C panic=abort
@@ -10,7 +8,5 @@ extern crate panic_runtime_unwind;
 fn main() {}
 
 //~? ERROR the linked panic runtime `panic_runtime_unwind` is not compiled with this crate's panic strategy `abort`
-// FIXME: These errors are target-dependent, could be served by some "optional error" annotation
-// instead of `dont-require-annotations`.
-//FIXME~? ERROR cannot link together two panic runtimes: panic_unwind and panic_runtime_unwind
-//FIXME~? ERROR the crate `panic_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`
+//~? ERROR? cannot link together two panic runtimes: panic_unwind and panic_runtime_unwind
+//~? ERROR? the crate `panic_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`
diff --git a/tests/ui/panic-runtime/want-abort-got-unwind2.rs b/tests/ui/panic-runtime/want-abort-got-unwind2.rs
index ddf12cd2a9a52..4ed2119d6f9e7 100644
--- a/tests/ui/panic-runtime/want-abort-got-unwind2.rs
+++ b/tests/ui/panic-runtime/want-abort-got-unwind2.rs
@@ -1,6 +1,4 @@
-// ignore-tidy-linelength
 //@ build-fail
-//@ dont-require-annotations: ERROR
 //@ dont-check-compiler-stderr
 //@ aux-build:panic-runtime-unwind.rs
 //@ aux-build:wants-panic-runtime-unwind.rs
@@ -11,7 +9,5 @@ extern crate wants_panic_runtime_unwind;
 fn main() {}
 
 //~? ERROR the linked panic runtime `panic_runtime_unwind` is not compiled with this crate's panic strategy `abort`
-// FIXME: These errors are target-dependent, could be served by some "optional error" annotation
-// instead of `dont-require-annotations`.
-//FIXME~? ERROR cannot link together two panic runtimes: panic_unwind and panic_runtime_unwind
-//FIXME~? ERROR the crate `panic_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`
+//~? ERROR? cannot link together two panic runtimes: panic_unwind and panic_runtime_unwind
+//~? ERROR? the crate `panic_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`