Fix ICE by rejecting const blocks in patterns during AST lowering (closes #148138)

[Shinonn23]

This PR fixes the ICE reported in #148138

The root cause is that const blocks aren’t allowed in pattern position, but the AST lowering logic still attempted to create PatExprKind::ConstBlock. That allowed invalid HIR to reach type checking, which then hit a span_bug!.

Following the discussion in the issue, this patch removes the ConstBlock lowering path from lower_expr_within_pat.
Any ExprKind::ConstBlock inside a pattern now lowers to PatKind::Err, consistent with how other invalid pattern expressions are handled.

A new UI test is included to ensure the compiler emits a proper error for const blocks in patterns and to prevent regressions.

Closes #148138

[rustbot]

r? @SparrowLii

rustbot has assigned @SparrowLii.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[dianne]

r? dianne

[rustbot]

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred in match checking

cc @Nadrieril

[Veykril]

This should not need to touch rust-analyzer source

View changes since this review

[dianne]

This is looking good now, thanks! Just a few more notes.
@rustbot author

View changes since this review

[dianne]

It'd be nice to keep this help message around. Could you add it to the ArbitraryExpressionInPattern error emitted during AST lowering? There's an optional pattern_from_macro_note note on it already, so you can use that as a reference (except making it a help rather than a note). We could also use the const blocks cannot be used as patterns message in that case too, but I could go either way on that; arbitrary expressions aren't allowed in patterns seems fine enough to me.

[Shinonn23]

Done!

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

diff of stderr:

5    |        ^
6    |
7    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
8 
9 error: arbitrary expressions aren't allowed in patterns
10   --> $DIR/issue-43250.rs:11:8

13    |        ^
14    |
15    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
16 
17 error: aborting due to 2 previous errors
18 


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args issues/issue-43250.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/issues/issue-43250.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/issues/issue-43250" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/issues/issue-43250.rs:9:8
   |
LL |     m!(y);
   |        ^
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/issues/issue-43250.rs:11:8
   |
LL |     m!(C);
   |        ^
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error: aborting due to 2 previous errors
------------------------------------------

---- [ui] tests/ui/issues/issue-43250.rs stdout end ----
---- [ui] tests/ui/lowering/expr-in-pat-issue-99380.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/lowering/expr-in-pat-issue-99380/expr-in-pat-issue-99380.stderr`
diff of stderr:

5    |          ^^^^^^^
6    |
7    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
8 
9 error: aborting due to 1 previous error
10 


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args lowering/expr-in-pat-issue-99380.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/lowering/expr-in-pat-issue-99380.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/lowering/expr-in-pat-issue-99380" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/lowering/expr-in-pat-issue-99380.rs:10:10
   |
LL |     foo!(Some(3)); //~ ERROR arbitrary expressions aren't allowed in patterns
   |          ^^^^^^^
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error: aborting due to 1 previous error
------------------------------------------

---- [ui] tests/ui/lowering/expr-in-pat-issue-99380.rs stdout end ----
---- [ui] tests/ui/match/expr_before_ident_pat.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/match/expr_before_ident_pat/expr_before_ident_pat.stderr`
diff of stderr:

11    |            ^
12    |
13    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
14 
15 error: aborting due to 2 previous errors
16 


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args match/expr_before_ident_pat.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/match/expr_before_ident_pat.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/match/expr_before_ident_pat" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0425]: cannot find value `a` in this scope
##[error]  --> /checkout/tests/ui/match/expr_before_ident_pat.rs:10:12
   |
LL |     funny!(a, a);
   |            ^ not found in this scope

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/match/expr_before_ident_pat.rs:10:12
   |
LL |     funny!(a, a);
   |            ^
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0425`.
------------------------------------------

---- [ui] tests/ui/match/expr_before_ident_pat.rs stdout end ----
---- [ui] tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock/ice-adjust-mode-unimplemented-for-constblock.stderr`
diff of stderr:

23    |
24 LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
25    |              ^^^^^^^^^^^^^^^^
+    |
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
26 
27 error[E0164]: expected tuple struct or tuple variant, found associated function `<[_]>::into_vec`
28   --> $DIR/ice-adjust-mode-unimplemented-for-constblock.rs:5:9


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0532]: expected a pattern, found a function call
##[error]  --> /checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
   |
LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
   |         ^^^^^^^^^^^^^^^^^^^^^^ not a tuple struct or tuple variant
   |
   = note: function calls are not allowed in patterns: <https://doc.rust-lang.org/book/ch19-00-patterns.html>
   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0658]: usage of qualified paths in this context is experimental
##[error]  --> /checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
   |
LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
   |         ^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #86935 <https://github.com/rust-lang/rust/issues/86935> for more information
   = help: add `#![feature(more_qualified_paths)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:5:14
   |
LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
   |              ^^^^^^^^^^^^^^^^
   |
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error[E0164]: expected tuple struct or tuple variant, found associated function `<[_]>::into_vec`
##[error]  --> /checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:5:9
   |
LL |     let vec![const { vec![] }]: Vec<usize> = vec![];
   |         ^^^^^^^^^^^^^^^^^^^^^^ `fn` calls are not allowed in patterns
   |
   = help: for more information, visit https://doc.rust-lang.org/book/ch19-00-patterns.html
   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 4 previous errors
---
diff of stderr:

8    |                               ----------- in this macro invocation
9    |
10    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
11    = note: this error originates in the macro `make_vec` (in Nightly builds, run with -Z macro-backtrace for more info)
12 
13 error: arbitrary expressions aren't allowed in patterns

20    |                         ----------- in this macro invocation
21    |
22    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
23    = note: this error originates in the macro `make_pat` (in Nightly builds, run with -Z macro-backtrace for more info)
24 
25 error: arbitrary expressions aren't allowed in patterns

32    |                         ----------- in this macro invocation
33    |
34    = note: the `expr` fragment specifier forces the metavariable's content to be an expression
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
35    = note: this error originates in the macro `make_pat` (in Nightly builds, run with -Z macro-backtrace for more info)
36 
37 error: aborting due to 3 previous errors


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args pattern/issue-92074-macro-ice.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/pattern/issue-92074-macro-ice.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/pattern/issue-92074-macro-ice" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/issue-92074-macro-ice.rs:18:25
   |
LL |     () => { force_expr!(Vec::new()) } //~ ERROR arbitrary expressions aren't allowed
   |                         ^^^^^^^^^^
...
LL |     assert!(matches!(x, En::A(make_vec!())));
   |                               ----------- in this macro invocation
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
   = note: this error originates in the macro `make_vec` (in Nightly builds, run with -Z macro-backtrace for more info)

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/issue-92074-macro-ice.rs:22:24
   |
LL |     () => { force_pat!(get_usize(), get_usize()) }
   |                        ^^^^^^^^^^^
...
LL |     assert!(matches!(5, make_pat!()));
   |                         ----------- in this macro invocation
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
   = note: this error originates in the macro `make_pat` (in Nightly builds, run with -Z macro-backtrace for more info)

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/issue-92074-macro-ice.rs:22:37
   |
LL |     () => { force_pat!(get_usize(), get_usize()) }
   |                                     ^^^^^^^^^^^
...
LL |     assert!(matches!(5, make_pat!()));
   |                         ----------- in this macro invocation
   |
   = note: the `expr` fragment specifier forces the metavariable's content to be an expression
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
   = note: this error originates in the macro `make_pat` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 3 previous errors
------------------------------------------

---- [ui] tests/ui/pattern/issue-92074-macro-ice.rs stdout end ----
---
3    |
4 LL |     Arith = 1 + 1,
5    |             ^^^^^
+    |
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
6 
7 error: arbitrary expressions aren't allowed in patterns
8   --> $DIR/patkind-litrange-no-expr.rs:20:13

10 LL |     Arith = 1 + 1,
11    |             ^^^^^
12    |
+    = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
13    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
14 
15 error: aborting due to 2 previous errors


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args pattern/patkind-litrange-no-expr.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/pattern/patkind-litrange-no-expr.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/pattern/patkind-litrange-no-expr" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/patkind-litrange-no-expr.rs:20:13
   |
LL |     Arith = 1 + 1, //~ ERROR arbitrary expressions aren't allowed in patterns
   |             ^^^^^
   |
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead

error: arbitrary expressions aren't allowed in patterns
##[error]  --> /checkout/tests/ui/pattern/patkind-litrange-no-expr.rs:20:13
   |
LL |     Arith = 1 + 1, //~ ERROR arbitrary expressions aren't allowed in patterns
   |             ^^^^^
   |
   = help: use a named `const`-item or an `if`-guard (`x if x == const { ... }`) instead
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 2 previous errors
------------------------------------------

---- [ui] tests/ui/pattern/patkind-litrange-no-expr.rs stdout end ----

[dianne]

Since the help message is specific to const blocks, it should only show up if the AST expression being lowered is actually a const block. It might be helpful to name its corresponding field as such too.