spack external find: show backtrace on error when --backtrace (#47082)

3 files changed, 16 insertions, 11 deletions

diff --git a/lib/spack/spack/detection/path.py b/lib/spack/spack/detection/path.py
index e8081f6e3c..d529f94f29 100644
--- a/lib/spack/spack/detection/path.py
+++ b/lib/spack/spack/detection/path.py
@@ -11,6 +11,7 @@ import os
 import os.path
 import re
 import sys
+import traceback
 import warnings
 from typing import Dict, Iterable, List, Optional, Set, Tuple, Type
 
@@ -18,6 +19,7 @@ import llnl.util.filesystem
 import llnl.util.lang
 import llnl.util.tty
 
+import spack.error
 import spack.spec
 import spack.util.elf as elf_utils
 import spack.util.environment
@@ -274,8 +276,12 @@ class Finder:
                 )
             except Exception as e:
                 specs = []
+                if spack.error.SHOW_BACKTRACE:
+                    details = traceback.format_exc()
+                else:
+                    details = f"[{e.__class__.__name__}: {e}]"
                 warnings.warn(
-                    f'error detecting "{pkg.name}" from prefix {candidate_path} [{str(e)}]'
+                    f'error detecting "{pkg.name}" from prefix {candidate_path}: {details}'
                 )
 
             if not specs:
@@ -449,9 +455,9 @@ def by_path(
                     llnl.util.tty.debug(
                         f"[EXTERNAL DETECTION] Skipping {pkg_name}: timeout reached"
                     )
-                except Exception as e:
+                except Exception:
                     llnl.util.tty.debug(
-                        f"[EXTERNAL DETECTION] Skipping {pkg_name}: exception occured {e}"
+                        f"[EXTERNAL DETECTION] Skipping {pkg_name}: {traceback.format_exc()}"
                     )
 
     return result
diff --git a/lib/spack/spack/error.py b/lib/spack/spack/error.py
index edb4b9e89f..45a39a4f20 100644
--- a/lib/spack/spack/error.py
+++ b/lib/spack/spack/error.py
@@ -12,6 +12,9 @@ import llnl.util.tty as tty
 #: this is module-scoped because it needs to be set very early
 debug = 0
 
+#: whether to show a backtrace when an error is printed, enabled with --backtrace.
+SHOW_BACKTRACE = False
+
 
 class SpackError(Exception):
     """This is the superclass for all Spack errors.
diff --git a/lib/spack/spack/main.py b/lib/spack/spack/main.py
index c0bb3d3355..7493e993ab 100644
--- a/lib/spack/spack/main.py
+++ b/lib/spack/spack/main.py
@@ -102,9 +102,6 @@ required_command_properties = ["level", "section", "description"]
 
 spack_ld_library_path = os.environ.get("LD_LIBRARY_PATH", "")
 
-#: Whether to print backtraces on error
-SHOW_BACKTRACE = False
-
 
 def add_all_commands(parser):
     """Add all spack subcommands to the parser."""
@@ -527,8 +524,7 @@ def setup_main_options(args):
 
     if args.debug or args.backtrace:
         spack.error.debug = True
-        global SHOW_BACKTRACE
-        SHOW_BACKTRACE = True
+        spack.error.SHOW_BACKTRACE = True
 
     if args.debug:
         spack.util.debug.register_interrupt_handler()
@@ -1021,19 +1017,19 @@ def main(argv=None):
         e.die()  # gracefully die on any SpackErrors
 
     except KeyboardInterrupt:
-        if spack.config.get("config:debug") or SHOW_BACKTRACE:
+        if spack.config.get("config:debug") or spack.error.SHOW_BACKTRACE:
             raise
         sys.stderr.write("\n")
         tty.error("Keyboard interrupt.")
         return signal.SIGINT.value
 
     except SystemExit as e:
-        if spack.config.get("config:debug") or SHOW_BACKTRACE:
+        if spack.config.get("config:debug") or spack.error.SHOW_BACKTRACE:
             traceback.print_exc()
         return e.code
 
     except Exception as e:
-        if spack.config.get("config:debug") or SHOW_BACKTRACE:
+        if spack.config.get("config:debug") or spack.error.SHOW_BACKTRACE:
             raise
         tty.error(e)
         return 3