Allow for missing invisible close delim when reparsing an expression.

This can happen when invalid syntax is passed to a declarative macro. We
shouldn't be too strict about the token stream position once the parser
has rejected the invalid syntax.

Fixes #139248.

Author: nnethercote

compiler/rustc_parse/src/parser/mod.rs

@@ -778,7 +778,10 @@ impl<'a> Parser<'a> {
                 self.bump();
                 Some(res)
             } else {
-                panic!("no close delim when reparsing {mv_kind:?}");
+                // This can occur when invalid syntax is passed to a decl macro. E.g. see #139248,
+                // where the reparse attempt of an invalid expr consumed the trailing invisible
+                // delimiter.
+                None
             }
         } else {
             None

tests/ui/macros/no-close-delim-issue-139248.rs

@@ -0,0 +1,9 @@
+// This code caused a "no close delim when reparsing Expr" ICE in #139248.
+
+thread_local! { static a : () = (if b) }
+//~^ error: expected `{`, found `)`
+//~| error: expected `{`, found `)`
+//~| error: expected `{`, found `)`
+//~| error: expected expression, found end of macro arguments
+
+fn main() {}

tests/ui/macros/no-close-delim-issue-139248.stderr

@@ -0,0 +1,51 @@
+error: expected `{`, found `)`
+  --> $DIR/no-close-delim-issue-139248.rs:3:38
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                      ^ expected `{`
+   |
+note: the `if` expression is missing a block after this condition
+  --> $DIR/no-close-delim-issue-139248.rs:3:37
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                     ^
+
+error: expected `{`, found `)`
+  --> $DIR/no-close-delim-issue-139248.rs:3:38
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                      ^ expected `{`
+   |
+note: the `if` expression is missing a block after this condition
+  --> $DIR/no-close-delim-issue-139248.rs:3:37
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                     ^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: expected `{`, found `)`
+  --> $DIR/no-close-delim-issue-139248.rs:3:38
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                      ^ expected `{`
+   |
+note: the `if` expression is missing a block after this condition
+  --> $DIR/no-close-delim-issue-139248.rs:3:37
+   |
+LL | thread_local! { static a : () = (if b) }
+   |                                     ^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: expected expression, found end of macro arguments
+  --> $DIR/no-close-delim-issue-139248.rs:3:1
+   |
+LL | thread_local! { static a : () = (if b) }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected expression
+  --> $SRC_DIR/std/src/sys/thread_local/native/mod.rs:LL:COL
+   |
+   = note: while parsing argument for this `expr` macro fragment
+   |
+   = note: this error originates in the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 4 previous errors
+