Rollup merge of #121917 - GuillaumeGomez:pattern-complexity_limit.rs, r=Nadrieril

Add new `pattern_complexity` attribute to add possibility to limit and check recursion in pattern matching

Needed for https://github.com/rust-lang/rust-analyzer/issues/9528.

This PR adds a new attribute only available when running rust testsuite called `pattern_complexity` which allows to set the maximum recursion for the pattern matching. It is quite useful to ensure the complexity doesn't grow, like in `tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs`.

r? `@Nadrieril`

5 files changed, 141 insertions, 0 deletions

diff --git a/tests/ui/feature-gates/feature-gate-pattern-complexity.rs b/tests/ui/feature-gates/feature-gate-pattern-complexity.rs
new file mode 100644
index 00000000000..43e9a00c9a7
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-pattern-complexity.rs
@@ -0,0 +1,6 @@
+// check that `pattern_complexity` is feature-gated
+
+#![pattern_complexity = "42"]
+//~^ ERROR: the `#[pattern_complexity]` attribute is just used for rustc unit tests
+
+fn main() {}
diff --git a/tests/ui/feature-gates/feature-gate-pattern-complexity.stderr b/tests/ui/feature-gates/feature-gate-pattern-complexity.stderr
new file mode 100644
index 00000000000..c05e6abb017
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-pattern-complexity.stderr
@@ -0,0 +1,12 @@
+error[E0658]: the `#[pattern_complexity]` attribute is just used for rustc unit tests and will never be stable
+  --> $DIR/feature-gate-pattern-complexity.rs:3:1
+   |
+LL | #![pattern_complexity = "42"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/pattern/complexity_limit.rs b/tests/ui/pattern/complexity_limit.rs
new file mode 100644
index 00000000000..c9a3f99bccd
--- /dev/null
+++ b/tests/ui/pattern/complexity_limit.rs
@@ -0,0 +1,106 @@
+#![feature(rustc_attrs)]
+#![pattern_complexity = "10000"]
+
+#[derive(Default)]
+struct BaseCommand {
+    field01: bool,
+    field02: bool,
+    field03: bool,
+    field04: bool,
+    field05: bool,
+    field06: bool,
+    field07: bool,
+    field08: bool,
+    field09: bool,
+    field10: bool,
+    field11: bool,
+    field12: bool,
+    field13: bool,
+    field14: bool,
+    field15: bool,
+    field16: bool,
+    field17: bool,
+    field18: bool,
+    field19: bool,
+    field20: bool,
+    field21: bool,
+    field22: bool,
+    field23: bool,
+    field24: bool,
+    field25: bool,
+    field26: bool,
+    field27: bool,
+    field28: bool,
+    field29: bool,
+    field30: bool,
+}
+
+fn request_key(command: BaseCommand) {
+    match command { //~ ERROR: reached pattern complexity limit
+        BaseCommand { field01: true, .. } => {}
+        BaseCommand { field02: true, .. } => {}
+        BaseCommand { field03: true, .. } => {}
+        BaseCommand { field04: true, .. } => {}
+        BaseCommand { field05: true, .. } => {}
+        BaseCommand { field06: true, .. } => {}
+        BaseCommand { field07: true, .. } => {}
+        BaseCommand { field08: true, .. } => {}
+        BaseCommand { field09: true, .. } => {}
+        BaseCommand { field10: true, .. } => {}
+        BaseCommand { field11: true, .. } => {}
+        BaseCommand { field12: true, .. } => {}
+        BaseCommand { field13: true, .. } => {}
+        BaseCommand { field14: true, .. } => {}
+        BaseCommand { field15: true, .. } => {}
+        BaseCommand { field16: true, .. } => {}
+        BaseCommand { field17: true, .. } => {}
+        BaseCommand { field18: true, .. } => {}
+        BaseCommand { field19: true, .. } => {}
+        BaseCommand { field20: true, .. } => {}
+        BaseCommand { field21: true, .. } => {}
+        BaseCommand { field22: true, .. } => {}
+        BaseCommand { field23: true, .. } => {}
+        BaseCommand { field24: true, .. } => {}
+        BaseCommand { field25: true, .. } => {}
+        BaseCommand { field26: true, .. } => {}
+        BaseCommand { field27: true, .. } => {}
+        BaseCommand { field28: true, .. } => {}
+        BaseCommand { field29: true, .. } => {}
+        BaseCommand { field30: true, .. } => {}
+
+        BaseCommand { field01: false, .. } => {}
+        BaseCommand { field02: false, .. } => {}
+        BaseCommand { field03: false, .. } => {}
+        BaseCommand { field04: false, .. } => {}
+        BaseCommand { field05: false, .. } => {}
+        BaseCommand { field06: false, .. } => {}
+        BaseCommand { field07: false, .. } => {}
+        BaseCommand { field08: false, .. } => {}
+        BaseCommand { field09: false, .. } => {}
+        BaseCommand { field10: false, .. } => {}
+        BaseCommand { field11: false, .. } => {}
+        BaseCommand { field12: false, .. } => {}
+        BaseCommand { field13: false, .. } => {}
+        BaseCommand { field14: false, .. } => {}
+        BaseCommand { field15: false, .. } => {}
+        BaseCommand { field16: false, .. } => {}
+        BaseCommand { field17: false, .. } => {}
+        BaseCommand { field18: false, .. } => {}
+        BaseCommand { field19: false, .. } => {}
+        BaseCommand { field20: false, .. } => {}
+        BaseCommand { field21: false, .. } => {}
+        BaseCommand { field22: false, .. } => {}
+        BaseCommand { field23: false, .. } => {}
+        BaseCommand { field24: false, .. } => {}
+        BaseCommand { field25: false, .. } => {}
+        BaseCommand { field26: false, .. } => {}
+        BaseCommand { field27: false, .. } => {}
+        BaseCommand { field28: false, .. } => {}
+        BaseCommand { field29: false, .. } => {}
+        BaseCommand { field30: false, .. } => {}
+    }
+}
+
+fn main() {
+    request_key(BaseCommand::default());
+}
diff --git a/tests/ui/pattern/complexity_limit.stderr b/tests/ui/pattern/complexity_limit.stderr
new file mode 100644
index 00000000000..08d9d40fe46
--- /dev/null
+++ b/tests/ui/pattern/complexity_limit.stderr
@@ -0,0 +1,14 @@
+error: reached pattern complexity limit
+  --> $DIR/complexity_limit.rs:39:5
+   |
+LL | /     match command {
+LL | |         BaseCommand { field01: true, .. } => {}
+LL | |         BaseCommand { field02: true, .. } => {}
+LL | |         BaseCommand { field03: true, .. } => {}
+...  |
+LL | |         BaseCommand { field30: false, .. } => {}
+LL | |     }
+   | |_____^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs b/tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs
index 984feef5f47..783512d5cca 100644
--- a/tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs
+++ b/tests/ui/pattern/usefulness/issue-118437-exponential-time-on-diagonal-match.rs
@@ -1,3 +1,6 @@
+#![feature(rustc_attrs)]
+#![pattern_complexity = "61"]
+
 //@ check-pass
 struct BaseCommand {
     field01: bool,