gdb/python: improve formatting of help text for user defined commands

Consider this command defined in Python (in the file test-cmd.py):

  class test_cmd (gdb.Command):
    """
    This is the first line.
      Indented second line.
    This is the third line.
    """

    def __init__ (self):
      super ().__init__ ("test-cmd", gdb.COMMAND_OBSCURE)

    def invoke (self, arg, from_tty):
      print ("In test-cmd")

  test_cmd()

Now, within a GDB session:

  (gdb) source test-cmd.py
  (gdb) help test-cmd

    This is the first line.
      Indented second line.
    This is the third line.

  (gdb)

I think there's three things wrong here:

  1. The leading blank line,
  2. The trailing blank line, and
  3. Every line is indented from the left edge slightly.

The problem of course, is that GDB is using the Python doc string
verbatim as its help text.  While the user has formatted the help text
so that it appears clear within the .py file, this means that the text
appear less well formatted when displayed in the "help" output.

The same problem can be observed for gdb.Parameter objects in their
set/show output.

In this commit I aim to improve the "help" output for commands and
parameters.

To do this I have added gdbpy_fix_doc_string_indentation, a new
function that rewrites the doc string text following the following
rules:

  1. Leading blank lines are removed,
  2. Trailing blank lines are removed, and
  3. Leading whitespace is removed in a "smart" way such that the
  relative indentation of lines is retained.

With this commit in place the above example now looks like this:

  (gdb) source ~/tmp/test-cmd.py
  (gdb) help test-cmd
  This is the first line.
    Indented second line.
  This is the third line.
  (gdb)

Which I think is much neater.  Notice that the indentation of the
second line is retained.  Any blank lines within the help text (not
leading or trailing) will be retained.

I've added a NEWS entry to note that there has been a change in
behaviour, but I didn't update the manual.  The existing manual is
suitably vague about how the doc string is used, so I think the new
behaviour is covered just as well by the existing text.

1 files changed, 282 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.python/py-doc-reformat.exp b/gdb/testsuite/gdb.python/py-doc-reformat.exp
new file mode 100644
index 0000000..aae3939
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-doc-reformat.exp
@@ -0,0 +1,282 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test how GDB reformats the documentation string of commands
+# implemented in Python for use as the help text of those same
+# commands.
+
+load_lib gdb-python.exp
+
+# A global counter used to number the tests.
+set idx 0
+
+# Run a test, create both a command and a parameter with INPUT_DOCS as
+# the Python documentation string, load the command and parameter into
+# GDB, and then ask for the help text of the command, and the show and
+# set help for the parameter.  The output from GDB should match
+# EXPECTED_OUTPUT in each case.
+#
+# The INPUT_DOCS must start with 2 space characters, followed by the
+# 3-quote characters to start the doc string, and must end with the
+# final 3-quote characters.  If this is not true then an error is
+# thrown, and this function immediately returns.
+proc test { input_docs expected_output } {
+    global idx
+
+    set local_idx $idx
+    incr idx
+
+    with_test_prefix "test ${local_idx}" {
+
+	# The tests in this script don't have descriptive names,
+	# rather they use the global IDX to generate a unique name for
+	# each test.  To make it easier to track down a failing test,
+	# we print out the test name and the input string.
+	verbose -log "Start of: test_cmd ${local_idx}"
+	verbose -log "Input:\n${input_docs}"
+
+	if { [string range $input_docs 0 4] != "  \"\"\"" } {
+	    perror "Input string does not start with the required pattern"
+	    return
+	}
+
+	if { [string range $input_docs end-2 end] != "\"\"\"" } {
+	    perror "Input string does not end with the required pattern"
+	    return
+	}
+
+	set python_filename [standard_output_file "${::gdb_test_file_name}-${local_idx}.py"]
+
+	set fd [open $python_filename w]
+
+	puts $fd "class test_cmd (gdb.Command):"
+	puts $fd $input_docs
+	puts $fd ""
+	puts $fd "  def __init__ (self):"
+	puts $fd "    super ().__init__ (\"test-cmd\", gdb.COMMAND_OBSCURE)"
+	puts $fd ""
+	puts $fd "  def invoke (self, arg, from_tty):"
+	puts $fd "    print (\"In test-cmd\")"
+	puts $fd ""
+
+	puts $fd "class test_param (gdb.Parameter):"
+	puts $fd $input_docs
+	puts $fd ""
+	puts $fd "  show_doc = \"This is the show doc line\""
+	puts $fd "  set_doc = \"This is the set doc line\""
+	puts $fd ""
+	puts $fd "  def __init__ (self):"
+	puts $fd "    super ().__init__ (\"test-param\", gdb.COMMAND_OBSCURE, gdb.PARAM_BOOLEAN)"
+	puts $fd ""
+	puts $fd "  def get_show_string (self, value):"
+	puts $fd "    return \"The state is '\" + value + \"'\""
+
+	puts $fd ""
+	puts $fd "test_param ()"
+	puts $fd "test_cmd ()"
+
+	puts $fd ""
+	puts $fd "print(\"Loaded OK.\")"
+
+	close $fd
+
+	set remote_python_file \
+	    [gdb_remote_download host $python_filename]
+
+	clean_restart
+
+	gdb_test "source ${remote_python_file}" \
+	    "Loaded OK\\." \
+	    "source python command file"
+
+	# Use gdb_test_multiple here as plain gdb_test will allow
+	# excess blank lines between the expected_output pattern and
+	# the gdb_prompt - a core part of this test is that we are
+	# checking that such blank lines are removed - so we can't use
+	# gdb_test here.
+	gdb_test_multiple "help test-cmd" "" {
+	    -re "^help test-cmd\r\n" {
+		exp_continue
+	    }
+	    -re "^$expected_output\r\n$::gdb_prompt $" {
+		pass $gdb_test_name
+	    }
+	}
+
+	gdb_test_multiple "help set test-param" "" {
+	    -re "^help set test-param\r\n" {
+		exp_continue
+	    }
+	    -re "^This is the set doc line\r\n" {
+		exp_continue
+	    }
+	    -re "^$expected_output\r\n$::gdb_prompt $" {
+		pass $gdb_test_name
+	    }
+	}
+
+	gdb_test_multiple "help show test-param" "" {
+	    -re "^help show test-param\r\n" {
+		exp_continue
+	    }
+	    -re "^This is the show doc line\r\n" {
+		exp_continue
+	    }
+	    -re "^$expected_output\r\n$::gdb_prompt $" {
+		pass $gdb_test_name
+	    }
+	}
+    }
+}
+
+# The first test is pretty vanilla. First line starts immediately
+# after the opening quotes, and closing quotes are immediately after
+# the last line.
+test \
+    [multi_line_input \
+	 "  \"\"\"This is the first line." \
+	 "" \
+	 "  This is the third line.\"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "" \
+	 "This is the third line\\."]
+
+# In this test the first line starts on the line after the opening
+# quotes.  The blank line in the middle is still completely empty.
+test \
+    [multi_line_input \
+	 "  \"\"\"" \
+	 "  This is the first line." \
+	 "" \
+	 "  This is the third line.\"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "" \
+	 "This is the third line\\."]
+
+# This test adds an indented line in the middle, we expect the
+# relative indentation to be retained.
+test\
+    [multi_line_input \
+	 "  \"\"\"" \
+	 "  This is the first line." \
+	 "    Indented second line." \
+	 "  This is the third line.\"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "  Indented second line\\." \
+	 "This is the third line\\."]
+
+# The indentation moves to the first line.
+test\
+    [multi_line_input \
+	 "  \"\"\"" \
+	 "    Indented first line." \
+	 "  This is the second line." \
+	 "  This is the third line.\"\"\""] \
+    [multi_line \
+	 "  Indented first line\\." \
+	 "This is the second line\\." \
+	 "This is the third line\\."]
+
+# The indentation moves to the last line.
+test\
+    [multi_line_input \
+	 "  \"\"\"" \
+	 "  This is the first line." \
+	 "  This is the second line." \
+	 "    Indented third line.\"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "This is the second line\\." \
+	 "  Indented third line\\."]
+
+# Tests using different amounts of white-space on a line of its own.
+# We test with the white-space at the beginning, end, and in the
+# middle of the doc string.
+foreach line [list "" " " "  " "   " "    "] {
+    # Blank lines at the beginning should be removed.
+    test \
+	[multi_line_input \
+	     "  \"\"\"" \
+	     $line \
+	     "  This is the first line." \
+	     "    Indented second line." \
+	     "  This is the third line.\"\"\""] \
+	[multi_line \
+	     "This is the first line\\." \
+	     "  Indented second line\\." \
+	     "This is the third line\\."]
+
+    # As should blank lines at the end.
+    test \
+	[multi_line_input \
+	     "  \"\"\"" \
+	     "  This is the first line." \
+	     "    Indented second line." \
+	     "  This is the third line." \
+	     $line \
+	     "  \"\"\""] \
+	[multi_line \
+	     "This is the first line\\." \
+	     "  Indented second line\\." \
+	     "This is the third line\\."]
+
+    # While blank lines in the middle should have all white-space
+    # removed.
+    test \
+	[multi_line_input \
+	     "  \"\"\"" \
+	     "  This is the first line." \
+	     $line \
+	     "  This is the third line." \
+	     $line \
+	     "  \"\"\""] \
+	[multi_line \
+	     "This is the first line\\." \
+	     "" \
+	     "This is the third line\\."]
+}
+
+# Check for correct handling of closing quotes being on a line of
+# their own.
+test\
+    [multi_line_input \
+	 "  \"\"\"  " \
+	 "  This is the first line." \
+	 "    Indented second line." \
+	 "  This is the third line." \
+	 "  \"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "  Indented second line\\." \
+	 "This is the third line\\." ]
+
+
+# Check with a single 'x' character before the closing quotes.  Make
+# sure we don't drop this character.
+test\
+    [multi_line_input \
+	 "  \"\"\"  " \
+	 "  This is the first line." \
+	 "    Indented second line." \
+	 "  This is the third line." \
+	 "  x\"\"\""] \
+    [multi_line \
+	 "This is the first line\\." \
+	 "  Indented second line\\." \
+	 "This is the third line\\." \
+	 "x"]