build: print a backtrace with the original metadata locations of Bash shell funcs

Leverage the comments that emit_var writes and the backtrace that
the shell func writes to generate an additional metadata-relative
backtrace. This will help the user troubleshoot shell funcs much
more easily.

Example:

| WARNING: /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955:171 exit 1 from 'exit 1'
| WARNING: Backtrace (BB generated script):
| 	#1: myclass_do_something, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 171
| 	#2: do_something, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 166
| 	#3: actually_fail, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 153
| 	#4: my_compile_extra, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 155
| 	#5: do_compile, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 141
| 	#6: main, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.68955, line 184
|
| Backtrace (metadata-relative locations):
| 	#1: myclass_do_something, /home/laplante/repos/oe-core/meta/classes/myclass.bbclass, line 2
| 	#2: do_something, autogenerated, line 2
| 	#3: actually_fail, /home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb, line 36
| 	#4: my_compile_extra, /home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb, line 38
| 	#5: do_compile, autogenerated, line 3
ERROR: Task (/home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb:do_compile) failed with exit code '1'
NOTE: Tasks Summary: Attempted 542 tasks of which 541 didn't need to be rerun and 1 failed.

Summary: 1 task failed:
  /home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb:do_compile
Summary: There was 1 ERROR message shown, returning a non-zero exit code.

Signed-off-by: Chris Laplante <chris.laplante@agilent.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Author: chris-laplante

lib/bb/build.py

@@ -16,7 +16,9 @@
 import sys
 import logging
 import glob
+import itertools
 import time
+import re
 import stat
 import bb
 import bb.msg
@@ -495,6 +497,62 @@ def readfifo(data):
             bb.debug(2, "Executing shell function %s" % func)
             with open(os.devnull, 'r+') as stdin, logfile:
                 bb.process.run(cmd, shell=False, stdin=stdin, log=logfile, extrafiles=[(fifo,readfifo)])
+        except bb.process.ExecutionError as exe:
+            # Find the backtrace that the shell trap generated
+            backtrace_marker_regex = re.compile(r"WARNING: Backtrace \(BB generated script\)")
+            stdout_lines = (exe.stdout or "").split("\n")
+            backtrace_start_line = None
+            for i, line in enumerate(reversed(stdout_lines)):
+                if backtrace_marker_regex.search(line):
+                    backtrace_start_line = len(stdout_lines) - i
+                    break
+
+            # Read the backtrace frames, starting at the location we just found
+            backtrace_entry_regex = re.compile(r"#(?P<frameno>\d+): (?P<funcname>[^\s]+), (?P<file>.+?), line ("
+                                               r"?P<lineno>\d+)")
+            backtrace_frames = []
+            if backtrace_start_line:
+                for line in itertools.islice(stdout_lines, backtrace_start_line, None):
+                    match = backtrace_entry_regex.search(line)
+                    if match:
+                        backtrace_frames.append(match.groupdict())
+
+            with open(runfile, "r") as script:
+                script_lines = [line.rstrip() for line in script.readlines()]
+
+            # For each backtrace frame, search backwards in the script (from the line number called out by the frame),
+            # to find the comment that emit_vars injected when it wrote the script. This will give us the metadata
+            # filename (e.g. .bb or .bbclass) and line number where the shell function was originally defined.
+            script_metadata_comment_regex = re.compile(r"# line: (?P<lineno>\d+), file: (?P<file>.+)")
+            better_frames = []
+            # Skip the very last frame since it's just the call to the shell task in the body of the script
+            for frame in backtrace_frames[:-1]:
+                # Check whether the frame corresponds to a function defined in the script vs external script.
+                if os.path.samefile(frame["file"], runfile):
+                    # Search backwards from the frame lineno to locate the comment that BB injected
+                    i = int(frame["lineno"]) - 1
+                    while i >= 0:
+                        match = script_metadata_comment_regex.match(script_lines[i])
+                        if match:
+                            # Calculate the relative line in the function itself
+                            relative_line_in_function = int(frame["lineno"]) - i - 2
+                            # Calculate line in the function as declared in the metadata
+                            metadata_function_line = relative_line_in_function + int(match["lineno"])
+                            better_frames.append("#{frameno}: {funcname}, {file}, line {lineno}".format(
+                                frameno=frame["frameno"],
+                                funcname=frame["funcname"],
+                                file=match["file"],
+                                lineno=metadata_function_line
+                            ))
+                            break
+                        i -= 1
+                else:
+                    better_frames.append("#{frameno}: {funcname}, {file}, line {lineno}".format(**frame))
+
+            if better_frames:
+                better_frames = ("\t{0}".format(frame) for frame in better_frames)
+                exe.extra_message = "\nBacktrace (metadata-relative locations):\n{0}".format("\n".join(better_frames))
+            raise
         finally:
             os.unlink(fifopath)
 

lib/bb/process.py

@@ -41,6 +41,7 @@ def __init__(self, command, exitcode, stdout = None, stderr = None):
         self.exitcode = exitcode
         self.stdout = stdout
         self.stderr = stderr
+        self.extra_message = None
 
     def __str__(self):
         message = ""
@@ -51,7 +52,7 @@ def __str__(self):
         if message:
             message = ":\n" + message
         return (CmdError.__str__(self) +
-                " with exit code %s" % self.exitcode + message)
+                " with exit code %s" % self.exitcode + message + (self.extra_message or ""))
 
 class Popen(subprocess.Popen):
     defaults = {