Disable CTFE if const_limit was set to 0, otherwise use the value set, which defaults to 1_000_000

src/librustc/middle/limits.rs

@@ -1,9 +1,9 @@
-// Registering limits, recursion_limit, type_length_limit and const_limit
-//
-// There are various parts of the compiler that must impose arbitrary limits
-// on how deeply they recurse to prevent stack overflow. Users can override
-// this via an attribute on the crate like `#![recursion_limit="22"]`. This pass
-// just peeks and looks for that attribute.
+//! Registering limits, recursion_limit, type_length_limit and const_limit
+//!
+//! There are various parts of the compiler that must impose arbitrary limits
+//! on how deeply they recurse to prevent stack overflow. Users can override
+//! this via an attribute on the crate like `#![recursion_limit="22"]`. This pass
+//! just peeks and looks for that attribute.
 
 use crate::session::Session;
 use core::num::IntErrorKind;
@@ -16,7 +16,7 @@ use rustc_data_structures::sync::Once;
 pub fn update_limits(sess: &Session, krate: &ast::Crate) {
     update_limit(sess, krate, &sess.recursion_limit, sym::recursion_limit, 128);
     update_limit(sess, krate, &sess.type_length_limit, sym::type_length_limit, 1048576);
-    update_limit(sess, krate, &sess.const_limit, sym::const_limit, 128);
+    update_limit(sess, krate, &sess.const_limit, sym::const_limit, 1_000_000);
 }
 
 fn update_limit(

src/test/ui/consts/const_limit/const_limit_not_reached.rs

@@ -0,0 +1,15 @@
+// run-pass
+#![feature(const_limit)]
+#![const_limit="1000"]
+
+const CONSTANT: usize = limit();
+
+fn main() {
+    assert_eq!(CONSTANT, 1764);
+}
+
+const fn limit() -> usize {
+    let x = 42;
+
+    x * 42
+}

src/test/ui/consts/const_limit/const_limit_overflow.rs

@@ -0,0 +1,15 @@
+// run-pass
+#![feature(const_limit)]
+#![const_limit="18_446_744_073_709_551_615"]
+
+const CONSTANT: usize = limit();
+
+fn main() {
+    assert_eq!(CONSTANT, 1764);
+}
+
+const fn limit() -> usize {
+    let x = 42;
+
+    x * 42
+}

src/test/ui/consts/const_limit/feature-gate-const_limit.rs

@@ -3,7 +3,9 @@
 
 const CONSTANT: usize = limit();
 
-fn main() {}
+fn main() {
+    assert_eq!(CONSTANT, 1764);
+}
 
 const fn limit() -> usize {
     let x = 42;