2 files changed, 71 insertions, 23 deletions

diff --git a/crates/test_utils/src/fixture.rs b/crates/test_utils/src/fixture.rs
index 6ba112de8..005a5c092 100644
--- a/crates/test_utils/src/fixture.rs
+++ b/crates/test_utils/src/fixture.rs
@@ -129,8 +129,18 @@ impl Fixture {
             if line.starts_with("//-") {
                 let meta = Fixture::parse_meta_line(line);
                 res.push(meta)
-            } else if let Some(entry) = res.last_mut() {
-                entry.text.push_str(line);
+            } else {
+                if line.starts_with("// ")
+                    && line.contains(":")
+                    && !line.contains("::")
+                    && line.chars().all(|it| !it.is_uppercase())
+                {
+                    panic!("looks like invalid metadata line: {:?}", line)
+                }
+
+                if let Some(entry) = res.last_mut() {
+                    entry.text.push_str(line);
+                }
             }
         }
 
@@ -154,7 +164,9 @@ impl Fixture {
         let mut env = FxHashMap::default();
         let mut introduce_new_source_root = false;
         for component in components[1..].iter() {
-            let (key, value) = component.split_once(':').unwrap();
+            let (key, value) = component
+                .split_once(':')
+                .unwrap_or_else(|| panic!("invalid meta line: {:?}", meta));
             match key {
                 "crate" => krate = Some(value.to_string()),
                 "deps" => deps = value.split(',').map(|it| it.to_string()).collect(),
@@ -276,38 +288,44 @@ impl MiniCore {
             }
         }
 
-        let mut curr_region = "";
+        let mut active_regions = Vec::new();
         let mut seen_regions = Vec::new();
         for line in lines {
             let trimmed = line.trim();
             if let Some(region) = trimmed.strip_prefix("// region:") {
-                assert_eq!(curr_region, "");
-                curr_region = region;
+                active_regions.push(region);
                 continue;
             }
             if let Some(region) = trimmed.strip_prefix("// endregion:") {
-                assert_eq!(curr_region, region);
-                curr_region = "";
+                let prev = active_regions.pop().unwrap();
+                assert_eq!(prev, region);
                 continue;
             }
-            seen_regions.push(curr_region);
 
-            let mut flag = curr_region;
+            let mut line_region = false;
             if let Some(idx) = trimmed.find("// :") {
-                flag = &trimmed[idx + "// :".len()..];
+                line_region = true;
+                active_regions.push(&trimmed[idx + "// :".len()..]);
             }
 
-            let skip = if flag == "" {
-                false
-            } else {
-                assert!(!flag.starts_with(' '), "region marker starts with a space: {:?}", flag);
-                self.assert_valid_flag(flag);
-                !self.has_flag(flag)
-            };
+            let mut keep = true;
+            for &region in &active_regions {
+                assert!(
+                    !region.starts_with(' '),
+                    "region marker starts with a space: {:?}",
+                    region
+                );
+                self.assert_valid_flag(region);
+                seen_regions.push(region);
+                keep &= self.has_flag(region);
+            }
 
-            if !skip {
+            if keep {
                 buf.push_str(line)
             }
+            if line_region {
+                active_regions.pop().unwrap();
+            }
         }
 
         for flag in &self.valid_flags {
@@ -315,7 +333,7 @@ impl MiniCore {
                 panic!("unused minicore flag: {:?}", flag);
             }
         }
-
+        format!("{}", buf);
         buf
     }
 }
diff --git a/crates/test_utils/src/minicore.rs b/crates/test_utils/src/minicore.rs
index 5ff60178c..e04ca58d2 100644
--- a/crates/test_utils/src/minicore.rs
+++ b/crates/test_utils/src/minicore.rs
@@ -9,11 +9,13 @@
 //!
 //! Available flags:
 //!     sized:
+//!     unsize: sized
+//!     coerce_unsized: unsize
 //!     slice:
 //!     range:
-//!     unsize: sized
 //!     deref: sized
-//!     coerce_unsized: unsize
+//!     deref_mut: deref
+//!     fn:
 //!     pin:
 //!     future: pin
 //!     option:
@@ -64,9 +66,16 @@ pub mod ops {
             type Target: ?Sized;
             fn deref(&self) -> &Self::Target;
         }
+        // region:deref_mut
+        #[lang = "deref_mut"]
+        pub trait DerefMut: Deref {
+            fn deref_mut(&mut self) -> &mut Self::Target;
+        }
+        // endregion:deref_mut
     }
     pub use self::deref::Deref;
-    // endregion:deref
+    pub use self::deref::DerefMut; //:deref_mut
+                                   // endregion:deref
 
     // region:range
     mod range {
@@ -104,6 +113,26 @@ pub mod ops {
     pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};
     pub use self::range::{RangeInclusive, RangeToInclusive};
     // endregion:range
+
+    // region:fn
+    mod function {
+        #[lang = "fn"]
+        #[fundamental]
+        pub trait Fn<Args>: FnMut<Args> {}
+
+        #[lang = "fn_mut"]
+        #[fundamental]
+        pub trait FnMut<Args>: FnOnce<Args> {}
+
+        #[lang = "fn_once"]
+        #[fundamental]
+        pub trait FnOnce<Args> {
+            #[lang = "fn_once_output"]
+            type Output;
+        }
+    }
+    pub use self::function::{Fn, FnMut, FnOnce};
+    // endregion:fn
 }
 
 // region:slice
@@ -181,6 +210,7 @@ pub mod prelude {
     pub mod v1 {
         pub use crate::{
             marker::Sized,                      // :sized
+            ops::{Fn, FnMut, FnOnce},           // :fn
             option::Option::{self, None, Some}, // :option
             result::Result::{self, Err, Ok},    // :result
         };