Rollup merge of #146828 - el-ev:issue146646, r=GuillaumeGomez

fix a crash in rustdoc merge finalize without input file

- Closes rust-lang/rust#146646

`SerializedSearchIndex::union` calls `Symbol::intern`, requiring `SESSION_GLOBALS` to be set.

3 files changed, 33 insertions, 2 deletions

diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 0ff1c090689..5d8f8f4bed1 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -836,8 +836,10 @@ fn main_args(early_dcx: &mut EarlyDiagCtxt, at_args: &[String]) {
         config::InputMode::NoInputMergeFinalize => {
             return wrap_return(
                 dcx,
-                run_merge_finalize(render_options)
-                    .map_err(|e| format!("could not write merged cross-crate info: {e}")),
+                rustc_span::create_session_globals_then(options.edition, &[], None, || {
+                    run_merge_finalize(render_options)
+                        .map_err(|e| format!("could not write merged cross-crate info: {e}"))
+                }),
             );
         }
     };
diff --git a/tests/run-make/rustdoc-merge-no-input-finalize/rmake.rs b/tests/run-make/rustdoc-merge-no-input-finalize/rmake.rs
new file mode 100644
index 00000000000..0b1e1948d5f
--- /dev/null
+++ b/tests/run-make/rustdoc-merge-no-input-finalize/rmake.rs
@@ -0,0 +1,28 @@
+// Running --merge=finalize without an input crate root should not trigger ICE.
+// Issue: https://github.com/rust-lang/rust/issues/146646
+
+//@ needs-target-std
+
+use run_make_support::{path, rustdoc};
+
+fn main() {
+    let out_dir = path("out");
+    let merged_dir = path("merged");
+    let parts_out_dir = path("parts");
+    rustdoc()
+        .input("sierra.rs")
+        .out_dir(&out_dir)
+        .arg("-Zunstable-options")
+        .arg(format!("--parts-out-dir={}", parts_out_dir.display()))
+        .arg("--merge=none")
+        .run();
+    assert!(parts_out_dir.join("crate-info").exists());
+
+    let output = rustdoc()
+        .arg("-Zunstable-options")
+        .out_dir(&out_dir)
+        .arg(format!("--include-parts-dir={}", parts_out_dir.display()))
+        .arg("--merge=finalize")
+        .run();
+    output.assert_stderr_not_contains("error: the compiler unexpectedly panicked. this is a bug.");
+}
diff --git a/tests/run-make/rustdoc-merge-no-input-finalize/sierra.rs b/tests/run-make/rustdoc-merge-no-input-finalize/sierra.rs
new file mode 100644
index 00000000000..f8fc48341ed
--- /dev/null
+++ b/tests/run-make/rustdoc-merge-no-input-finalize/sierra.rs
@@ -0,0 +1 @@
+pub struct Sierra;