From 6166addc822a819b60144339ce4094e1b24fc6ad Mon Sep 17 00:00:00 2001
From: Urgau <urgau@numericable.fr>
Date: Mon, 10 Aug 2026 19:01:36 +0200
Subject: [PATCH] Add nightly-only support for Cargo unremap trim-paths files
 in rust-lldb

---
 src/bootstrap/src/core/build_steps/dist.rs |   3 +
 src/etc/lldb_trim_paths.py                 | 115 +++++++++++++++++++++
 src/etc/rust-lldb                          |   8 ++
 3 files changed, 126 insertions(+)
 create mode 100644 src/etc/lldb_trim_paths.py

diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index 404d7d7b2aab0..8e9fb305084f6 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -761,6 +761,9 @@ impl Step for DebuggerScripts {
 
         cp_debugger_script("lldb_lookup.py");
         cp_debugger_script("lldb_providers.py");
+        if builder.build.unstable_features() {
+            cp_debugger_script("lldb_trim_paths.py");
+        }
     }
 }
 
diff --git a/src/etc/lldb_trim_paths.py b/src/etc/lldb_trim_paths.py
new file mode 100644
index 0000000000000..0084c15ab7dde
--- /dev/null
+++ b/src/etc/lldb_trim_paths.py
@@ -0,0 +1,115 @@
+# LLDB Python script to handle Cargo `<exe>.trim-paths.jsonl` files from the trim-paths feature
+#  - https://github.com/rust-lang/cargo/issues/12137
+#  - https://github.com/rust-lang/rust/issues/111540
+
+import json
+import os
+import sys
+import lldb
+import threading
+
+
+def _process_v1_trim_paths(debugger, lines, trim_paths_path):
+    for idx, line in enumerate(lines[2:], start=3):
+        try:
+            entry = json.loads(line)
+            if "from" in entry and "to" in entry:
+                # LLDB syntax: settings append target.source-map <from> <to>
+                cmd = f'settings append target.source-map "{entry["from"]}" "{entry["to"]}"'
+                debugger.HandleCommand(cmd)
+        except json.JSONDecodeError:
+            print(
+                f"(rust-lldb) warning: invalid JSON on line {idx} of {trim_paths_path}",
+                file=sys.stderr,
+            )
+
+
+def _load_trim_paths(debugger, filepath):
+    trim_paths_path = f"{filepath}.trim-paths.jsonl"
+
+    if not os.path.isfile(trim_paths_path):
+        return
+
+    try:
+        # Load all the lines of the trim-paths file
+        with open(trim_paths_path, "r", encoding="utf-8") as f:
+            lines = [line.strip() for line in f]
+
+        # Abort if we have less than 3 lines as that means that we cannot have any
+        # substitutions (header + metadata is already 2 lines)
+        if not lines or len(lines) < 3:
+            return
+
+        # Try loading the header line, which contains the version (v) field
+        try:
+            header = json.loads(lines[0])
+            ver = header.get("v")
+        except json.JSONDecodeError:
+            print(
+                f"(rust-lldb) warning: header line 1 of {trim_paths_path} is not valid JSON",
+                file=sys.stderr,
+            )
+            return
+
+        # We only handle version 1
+        if ver == 1:
+            _process_v1_trim_paths(debugger, lines, trim_paths_path)
+        else:
+            print(
+                f"(rust-lldb) warning: unsupported trim-paths version {ver}: {trim_paths_path}",
+                file=sys.stderr,
+            )
+    except Exception as e:
+        print(
+            f"(rust-lldb) warning: failed to process trim-paths mappings: {e} of {trim_paths_path}",
+            file=sys.stderr,
+        )
+
+
+def _on_target(debugger, target):
+    # https://lldb.llvm.org/python_reference/lldb.SBTarget-class.html
+    if not target or not target.IsValid():
+        return
+
+    for module in target.module_iter():
+        # SBFileSpec for the module's file on the host machine
+        # https://lldb.llvm.org/python_reference/lldb.SBFileSpec-class.html
+        file_spec = module.GetFileSpec()
+
+        filepath = os.path.join(file_spec.GetDirectory(), file_spec.GetFilename())
+
+        _load_trim_paths(debugger, filepath)
+
+
+def _listen_for_new_targets(debugger):
+    listener = lldb.SBListener("rust_lldb_target_listener")
+
+    # Listen for loaded modules
+    listener.StartListeningForEventClass(
+        debugger,
+        lldb.SBTarget.GetBroadcasterClassName(),
+        lldb.SBTarget.eBroadcastBitModulesLoaded,
+    )
+
+    while True:
+        event = lldb.SBEvent()
+
+        if not listener.WaitForEvent(1, event):
+            continue
+        if not lldb.SBTarget.EventIsTargetEvent(event):
+            continue
+
+        target = debugger.GetSelectedTarget()
+        _on_target(debugger, target)
+
+
+def __lldb_init_module(debugger, internal_dict):
+    # Process any existing target present on module load
+    target = debugger.GetSelectedTarget()
+    _on_target(debugger, target)
+
+    # Start background thread to listen to event in the background
+    listener_thread = threading.Thread(
+        target=_listen_for_new_targets, args=(debugger,), daemon=True
+    )
+    listener_thread.start()
diff --git a/src/etc/rust-lldb b/src/etc/rust-lldb
index 91c6591171392..c99357f324989 100755
--- a/src/etc/rust-lldb
+++ b/src/etc/rust-lldb
@@ -32,5 +32,13 @@ fi
 
 script_import="command script import \"$RUSTC_SYSROOT/lib/rustlib/etc/lldb_lookup.py\""
 
+# Unstable (nightly-only) trim-paths feature, activated only if
+#  - RUST_LLDB_TRIM_PATHS=unstable is set
+#  - and if the python file is present (only shipped on nightly)
+LLDB_TRIM_PATHS="$RUSTC_SYSROOT/lib/rustlib/etc/lldb_trim_paths.py"
+if [ "${RUST_LLDB_TRIM_PATHS:-}" = "unstable" ] && [ -f "$LLDB_TRIM_PATHS" ]; then
+    set -- --one-line-before-file "command script import \"$LLDB_TRIM_PATHS\"" "$@"
+fi
+
 # Call LLDB with the commands added to the argument list
 exec "$lldb" --one-line-before-file "$script_import" "$@"