Figuring out call stack introspection in bash via spec tests.

It appears the variables that collectively store the call stack don't
line up!  ${BASH_SOURCE[i]} and ${BASH_LINENO[i]} are out of whack!

But the current position is ${BASH_SOURCE[0]} and $LINENO.  Sigh.

This was good to test out, but I don't think Oil will compatible with
bash (and hence debuggers like bashdb).

Also:
- Test the values of $$ and $BASHPID in command subs too.

core/alloc.py

@@ -116,16 +116,16 @@ def GetDebugInfo(self, line_id):
def CompletionArena(pool):
  """A temporary arena that only exists for a function call?"""
  arena = pool.NewArena()
  arena.PushSource('<completion>')
  arena.PushSource('<temp completion buffer>')
  return arena


def PluginArena():
def PluginArena(source_name):
  """For PS4, etc."""
  # TODO: Should there only be one pool?  This isn't worked out yet.
  pool = Pool()
  arena = pool.NewArena()
  arena.PushSource('<plugin>')
  arena.PushSource(source_name)
  return arena

core/cmd_exec.py

@@ -1115,7 +1115,7 @@ def __init__(self, exec_opts, mem, word_ev):
    self.mem = mem
    self.word_ev = word_ev

    self.arena = alloc.PluginArena()
    self.arena = alloc.PluginArena('<$PS4>')
    self.parse_cache = {}  # PS4 value -> CompoundWord.  PS4 is scoped.

  def OnSimpleCommand(self, argv):

spec/introspect.test.sh

@@ -1,16 +1,86 @@
#!/usr/bin/env bash
#
# TODO:
# BASH_SOURCE, BASH_LINENO, caller builtin
# Test call stack introspection.  There are a bunch of special variables
# defined here:
#
# https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html
# 
# - The shell function ${FUNCNAME[$i]} is defined in the file
#   ${BASH_SOURCE[$i]} and called from ${BASH_SOURCE[$i+1]}
#
# - ${BASH_LINENO[$i]} is the line number in the source file
#   (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or
#   ${BASH_LINENO[$i-1]} if referenced within another shell function). 
#
# - For instance, ${FUNCNAME[$i]} was called from the file
#   ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The caller builtin
#   displays the current call stack using this information. 
#
# So ${BASH_SOURCE[@]} doesn't line up with ${BASH_LINENO}.  But
# ${BASH_SOURCE[0]} does line up with $LINENO!
#
# Geez.


### ${FUNCNAME[@]} array
g() {
  argv.py "${FUNCNAME[@]}"
}
f() {
  argv.py "${FUNCNAME[@]}"
  g
  argv.py "${FUNCNAME[@]}"
}
f
## STDOUT: 
['f']
['g', 'f']
['f']
## END

### ${BASH_SOURCE[@]} is a stack of source files for function calls
$SH spec/testdata/bash-source.sh
## STDOUT: 
['begin F funcs', 'f', 'main']
['begin F files', 'spec/testdata/bash-source.sh', 'spec/testdata/bash-source.sh']
['begin F lines', '21', '0']
['G funcs', 'g', 'f', 'main']
['G files', 'spec/testdata/bash-source-2.sh', 'spec/testdata/bash-source.sh', 'spec/testdata/bash-source.sh']
['G lines', '15', '21', '0']
['end F funcs', 'f', 'main']
['end F', 'spec/testdata/bash-source.sh', 'spec/testdata/bash-source.sh']
['end F lines', '21', '0']
## END

### ${BASH_LINENO[@]} is a stack of line numbers for function calls
# note: it's CALLS, not DEFINITIONS.
g() {
  argv.py "${FUNCNAME[@]}"
  argv.py G "${BASH_LINENO[@]}"
}
f() {
  argv.py 'begin F' "${BASH_LINENO[@]}"
  g  # line 6
  argv.py 'end F' "${BASH_LINENO[@]}"
}
f  # line 9
## STDOUT: 
['begin F', '9']
['G', '6', '9']
['end F', '9']
## END

### $LINENO is the current line, not line of function call
g() {
  argv.py $LINENO  # line 2
}
f() {
  argv.py $LINENO  # line 5
  g
  argv.py $LINENO  # line 7
}
f
# stdout-json: "['f']\n['g', 'f']\n['f']\n"
## STDOUT: 
['5']
['2']
['7']
## END

spec/special-vars.test.sh

@@ -3,6 +3,14 @@
# NOTE:
# - $! is tested in background.test.sh
# - $- is tested in sh-options
#
# TODO: It would be nice to make a table, like:
#
# $$  $BASHPID  $PPID   $SHLVL   $BASH_SUBSHELL
#  X 
# (Subshell,  Command Sub,  Pipeline,  Spawn $0)
#
# And see whether the variable changed.

### $PWD
# Just test that it has a slash for now.
@@ -39,7 +47,7 @@ echo $_
echo $$ | egrep '[0-9]+'
# status: 0

### $$ doesn't change with subshell
### $$ doesn't change with subshell or command sub
# Just test that it has decimal digits
set -o errexit
die() {
@@ -48,28 +56,48 @@ die() {
parent=$$
test -n "$parent" || die "empty PID in parent"
( child=$$
  test -n "$child" || die "empty PID in child"
  test -n "$child" || die "empty PID in subshell"
  test "$parent" = "$child" || die "should be equal: $parent != $child"
  echo 'subshell OK'
)
echo $( child=$$
        test -n "$child" || die "empty PID in command sub"
        test "$parent" = "$child" || die "should be equal: $parent != $child"
        echo 'command sub OK'
      )
exit 3  # make sure we got here
# stdout-json: ""
# status: 3
## STDOUT:
subshell OK
command sub OK
## END

### $BASHPID DOES change with subshell
### $BASHPID DOES change with subshell and command sub
set -o errexit
die() {
  echo 1>&2 "$@"; exit 1
}
parent=$BASHPID
test -n "$parent" || die "empty BASHPID in parent"
( child=$BASHPID
  test -n "$child" || die "empty BASHPID in child"
  test -n "$child" || die "empty BASHPID in subshell"
  test "$parent" != "$child" || die "should not be equal: $parent = $child"
  echo 'subshell OK'
)
echo $( child=$BASHPID
        test -n "$child" || die "empty BASHPID in command sub"
        test "$parent" != "$child" ||
          die "should not be equal: $parent = $child"
        echo 'command sub OK'
      )
exit 3  # make sure we got here
# stdout-json: ""
# status: 3
# N-I dash status: 1
## status: 3
## STDOUT:
subshell OK
command sub OK
## END
## N-I dash status: 1
## N-I dash stdout-json: ""

### Background PID $! looks like a PID
sleep 0.01 &

spec/testdata/bash-source-2.sh

@@ -0,0 +1,7 @@
#!/bin/bash

g() {
  argv 'G funcs' "${FUNCNAME[@]}" 
  argv 'G files' "${BASH_SOURCE[@]}"
  argv 'G lines' "${BASH_LINENO[@]}" 
}

spec/testdata/bash-source.sh

@@ -0,0 +1,21 @@
#!/usr/bin/env bash
#
# For spec/introspect.test.sh.

source spec/testdata/bash-source-2.sh

argv() {
  spec/bin/argv.py "$@"
}

f() {
  argv 'begin F funcs' "${FUNCNAME[@]}" 
  argv 'begin F files' "${BASH_SOURCE[@]}" 
  argv 'begin F lines' "${BASH_LINENO[@]}" 
  g
  argv 'end F funcs' "${FUNCNAME[@]}" 
  argv 'end F' "${BASH_SOURCE[@]}"
  argv 'end F lines' "${BASH_LINENO[@]}" 
}

f  # call a function it defines