Move parsing of CSI escape sequences into dedicated functions

This breaks up the deeply indented blocks which implemented this in
pty.Parser.parse() before. It also allows us to simplify the control
flow a bit: The two nested try … except blocks for StopIteration (to
detect if we need to postpone parsing) and AssertionError (to detect
if we don't understand what looked like an escape sequence or handle
other parse errors) into a single one.

1 files changed, 182 insertions, 159 deletions

diff --git a/saneterm/pty.py b/saneterm/pty.py
index c6fda6a..6940c6e 100644
--- a/saneterm/pty.py
+++ b/saneterm/pty.py
@@ -309,6 +309,171 @@ def parse_extended_color(iterator):
         # … but who needs these?
         raise AssertionError("unsupported extended color")
 
+
+def parse_sgr_sequence(params, special_evs):
+    """
+    SGR (Select Graphic Rendition) sequence:
+    any number of numbers separated by ';'
+    which change the current text presentation.
+    If the parameter string is empty, a single '0'
+    is implied.
+
+    We support a subset of the core SGR sequences
+    as specified by ECMA-48. Most notably we also
+    support the common additional bright color
+    sequences. This also justifies not to implement
+    the strange behavior of choosing brighter colors
+    when the current text is bold.
+
+    We also support ':' as a separator which is
+    only necessary for extended color sequences
+    as specified in ITU-T Rec. T.416 | ISO/IEC 8613-6
+    (see also parse_extended_color()). Actually
+    those sequences _must_ use colons and semicolons
+    would be invalid. In reality, however, the
+    incorrect usage of semicolons seems to be much
+    more common. Thus we are extremely lenient and
+    allow both ':' and ';' as well as a mix of both
+    as separators.
+    """
+    args = re.split(r'[:;]', params)
+
+    arg_it = iter(args)
+    for arg in arg_it:
+        if len(arg) == 0:
+            # empty implies 0
+            sgr_type = 0
+        else:
+            try:
+                sgr_type = int(arg)
+            except ValueError:
+                raise AssertionError("Invalid Integer")
+
+        change_payload = None
+
+        # Not supported:
+        #   5-6     blink
+        #   7       invert
+        #   10      default font
+        #   11-19   alternative font
+        #   20      blackletter font
+        #   25      disable blinking
+        #   26      proportional spacing
+        #   27      disable inversion
+        #   50      disable proportional spacing
+        #   51      framed
+        #   52      encircled
+        #   53      overlined (TODO: implement via GTK 4 TextTag)
+        #   54      neither framed nor encircled
+        #   55      not overlined
+        #   60-65   ideograms (TODO: find out what this is supposed to do)
+        #   58-59   underline color, non-standard
+        #   73-65   sub/superscript, non-standard (TODO: via scale and rise)
+        if sgr_type == 0:
+            change_payload = (TextStyleChange.RESET, None)
+        elif sgr_type == 1:
+            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.BOLD)
+        elif sgr_type == 2:
+            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.THIN)
+        elif sgr_type == 3:
+            change_payload = (TextStyleChange.ITALIC, True)
+        elif sgr_type == 4:
+            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.SINGLE)
+        elif sgr_type == 8:
+            change_payload = (TextStyleChange.CONCEALED, True)
+        elif sgr_type == 9:
+            change_payload = (TextStyleChange.STRIKETHROUGH, True)
+        elif sgr_type == 21:
+            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.DOUBLE)
+        elif sgr_type == 22:
+            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.NORMAL)
+        elif sgr_type == 23:
+            # also theoretically should disable blackletter
+            change_payload = (TextStyleChange.ITALIC, False)
+        elif sgr_type == 24:
+            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.NONE)
+        elif sgr_type == 28:
+            change_payload = (TextStyleChange.CONCEALED, False)
+        elif sgr_type == 29:
+            change_payload = (TextStyleChange.STRIKETHROUGH, False)
+        elif sgr_type >= 30 and sgr_type <= 37:
+            change_payload = (
+                TextStyleChange.FOREGROUND_COLOR,
+                Color(
+                    ColorType.NUMBERED_8,
+                    BasicColor(sgr_type - 30)
+                )
+            )
+        elif sgr_type == 38:
+            try:
+                change_payload = (
+                    TextStyleChange.FOREGROUND_COLOR,
+                    parse_extended_color(arg_it)
+                )
+            except AssertionError:
+                # TODO: maybe fail here?
+                pass
+        elif sgr_type == 39:
+            change_payload = (TextStyleChange.FOREGROUND_COLOR, None)
+        elif sgr_type >= 40 and sgr_type <= 47:
+            change_payload = (
+                TextStyleChange.BACKGROUND_COLOR,
+                Color(
+                    ColorType.NUMBERED_8,
+                    BasicColor(sgr_type - 40)
+                )
+            )
+        elif sgr_type == 48:
+            try:
+                change_payload = (
+                    TextStyleChange.BACKGROUND_COLOR,
+                    parse_extended_color(arg_it)
+                )
+            except AssertionError:
+                # TODO: maybe fail here?
+                pass
+        elif sgr_type == 49:
+            change_payload = (TextStyleChange.BACKGROUND_COLOR, None)
+        elif sgr_type >= 90 and sgr_type <= 97:
+            change_payload = (
+                TextStyleChange.FOREGROUND_COLOR,
+                Color(
+                    ColorType.NUMBERED_8_BRIGHT,
+                    BasicColor(sgr_type - 90)
+                )
+            )
+        elif sgr_type >= 100 and sgr_type <= 107:
+            change_payload = (
+                TextStyleChange.BACKGROUND_COLOR,
+                Color(
+                    ColorType.NUMBERED_8_BRIGHT,
+                    BasicColor(sgr_type - 100)
+                )
+            )
+
+        if change_payload != None:
+            special_evs.append((EventType.TEXT_STYLE, change_payload))
+
+def parse_csi_sequence(it, special_evs):
+    """
+    Parses control sequences which begin with a
+    Control Sequence Introducer (CSI) as specified
+    in ECMA-48, section 5.4.
+    Supported escape sequences append events to
+    special_evs while unsupported ones are ignored,
+    and thus filtered out.
+    """
+    params = it.takewhile_greedy(csi_parameter_byte)
+    inters = it.takewhile_greedy(csi_intermediate_byte)
+    final = it.next()
+
+    assert csi_final_byte(final)
+
+    # Unsupported CSI sequences are ignored which reduces
+    # the noise from unsupported sequences
+    if final == 'm':
+        parse_sgr_sequence(params, special_evs)
+
 class Parser(object):
     """
     Parses a subset of special control sequences read from
@@ -390,161 +555,7 @@ class Parser(object):
 
                     try:
                         if it.next() == '[':
-                            # CSI sequence
-                            try:
-                                params = it.takewhile_greedy(csi_parameter_byte)
-                                inters = it.takewhile_greedy(csi_intermediate_byte)
-                                final = it.next()
-
-                                assert csi_final_byte(final)
-
-                                if final == 'm':
-                                    # SGR (Select Graphic Rendition) sequence:
-                                    # any number of numbers separated by ';'
-                                    # which change the current text presentation.
-                                    # If the parameter string is empty, a single '0'
-                                    # is implied.
-                                    #
-                                    # We support a subset of the core SGR sequences
-                                    # as specified by ECMA-48. Most notably we also
-                                    # support the common additional bright color
-                                    # sequences. This also justifies not to implement
-                                    # the strange behavior of choosing brighter colors
-                                    # when the current text is bold.
-                                    #
-                                    # We also support ':' as a separator which is
-                                    # only necessary for extended color sequences
-                                    # as specified in ITU-T Rec. T.416 | ISO/IEC 8613-6
-                                    # (see also parse_extended_color()). Actually
-                                    # those sequences _must_ use colons and semicolons
-                                    # would be invalid. In reality, however, the
-                                    # incorrect usage of semicolons seems to be much
-                                    # more common. Thus we are extremely lenient and
-                                    # allow both ':' and ';' as well as a mix of both
-                                    # as separators.
-                                    args = re.split(r'[:;]', params)
-
-                                    arg_it = iter(args)
-                                    for arg in arg_it:
-                                        if len(arg) == 0:
-                                            # empty implies 0
-                                            sgr_type = 0
-                                        else:
-                                            try:
-                                                sgr_type = int(arg)
-                                            except ValueError:
-                                                raise AssertionError("Invalid Integer")
-
-                                        change_payload = None
-
-                                        # Not supported:
-                                        #   5-6     blink
-                                        #   7       invert
-                                        #   10      default font
-                                        #   11-19   alternative font
-                                        #   20      blackletter font
-                                        #   25      disable blinking
-                                        #   26      proportional spacing
-                                        #   27      disable inversion
-                                        #   50      disable proportional spacing
-                                        #   51      framed
-                                        #   52      encircled
-                                        #   53      overlined (TODO: implement via GTK 4 TextTag)
-                                        #   54      neither framed nor encircled
-                                        #   55      not overlined
-                                        #   60-65   ideograms (TODO: find out what this is supposed to do)
-                                        #   58-59   underline color, non-standard
-                                        #   73-65   sub/superscript, non-standard (TODO: via scale and rise)
-                                        if sgr_type == 0:
-                                            change_payload = (TextStyleChange.RESET, None)
-                                        elif sgr_type == 1:
-                                            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.BOLD)
-                                        elif sgr_type == 2:
-                                            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.THIN)
-                                        elif sgr_type == 3:
-                                            change_payload = (TextStyleChange.ITALIC, True)
-                                        elif sgr_type == 4:
-                                            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.SINGLE)
-                                        elif sgr_type == 8:
-                                            change_payload = (TextStyleChange.CONCEALED, True)
-                                        elif sgr_type == 9:
-                                            change_payload = (TextStyleChange.STRIKETHROUGH, True)
-                                        elif sgr_type == 21:
-                                            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.DOUBLE)
-                                        elif sgr_type == 22:
-                                            change_payload = (TextStyleChange.WEIGHT, Pango.Weight.NORMAL)
-                                        elif sgr_type == 23:
-                                            # also theoretically should disable blackletter
-                                            change_payload = (TextStyleChange.ITALIC, False)
-                                        elif sgr_type == 24:
-                                            change_payload = (TextStyleChange.UNDERLINE, Pango.Underline.NONE)
-                                        elif sgr_type == 28:
-                                            change_payload = (TextStyleChange.CONCEALED, False)
-                                        elif sgr_type == 29:
-                                            change_payload = (TextStyleChange.STRIKETHROUGH, False)
-                                        elif sgr_type >= 30 and sgr_type <= 37:
-                                            change_payload = (
-                                                TextStyleChange.FOREGROUND_COLOR,
-                                                Color(
-                                                    ColorType.NUMBERED_8,
-                                                    BasicColor(sgr_type - 30)
-                                                )
-                                            )
-                                        elif sgr_type == 38:
-                                            try:
-                                                change_payload = (
-                                                    TextStyleChange.FOREGROUND_COLOR,
-                                                    parse_extended_color(arg_it)
-                                                )
-                                            except AssertionError:
-                                                # TODO: maybe fail here?
-                                                pass
-                                        elif sgr_type == 39:
-                                            change_payload = (TextStyleChange.FOREGROUND_COLOR, None)
-                                        elif sgr_type >= 40 and sgr_type <= 47:
-                                            change_payload = (
-                                                TextStyleChange.BACKGROUND_COLOR,
-                                                Color(
-                                                    ColorType.NUMBERED_8,
-                                                    BasicColor(sgr_type - 40)
-                                                )
-                                            )
-                                        elif sgr_type == 48:
-                                            try:
-                                                change_payload = (
-                                                    TextStyleChange.BACKGROUND_COLOR,
-                                                    parse_extended_color(arg_it)
-                                                )
-                                            except AssertionError:
-                                                # TODO: maybe fail here?
-                                                pass
-                                        elif sgr_type == 49:
-                                            change_payload = (TextStyleChange.BACKGROUND_COLOR, None)
-                                        elif sgr_type >= 90 and sgr_type <= 97:
-                                            change_payload = (
-                                                TextStyleChange.FOREGROUND_COLOR,
-                                                Color(
-                                                    ColorType.NUMBERED_8_BRIGHT,
-                                                    BasicColor(sgr_type - 90)
-                                                )
-                                            )
-                                        elif sgr_type >= 100 and sgr_type <= 107:
-                                            change_payload = (
-                                                TextStyleChange.BACKGROUND_COLOR,
-                                                Color(
-                                                    ColorType.NUMBERED_8_BRIGHT,
-                                                    BasicColor(sgr_type - 100)
-                                                )
-                                            )
-
-                                        if change_payload != None:
-                                            special_evs.append((EventType.TEXT_STYLE, change_payload))
-
-
-                            except AssertionError:
-                                # invalid CSI sequence, we'll render it as text for now
-                                ignore_esc = True
-
+                            parse_csi_sequence(it, special_evs)
                         else:
                             # we only parse CSI sequences for now, all other
                             # sequences will be rendered as text to the terminal.
@@ -552,10 +563,10 @@ class Parser(object):
                             # we also want to filter out, e. g. OSC sequences
                             ignore_esc = True
 
-                        # with only backtracks if the end of input is
-                        # reached, so we do need to do it explicitly here.
-                        if ignore_esc:
-                            it.backtrack()
+                    except AssertionError:
+                        # AssertionError indicates a parse error, we'll render
+                        # a escape sequence we can't parse verbatim for now
+                        ignore_esc = True
 
                     except StopIteration:
                         # the full escape sequence wasn't contained in
@@ -566,6 +577,18 @@ class Parser(object):
                         # exhausted.
                         self.__leftover = it.wrapped[flush_until:]
 
+                        # prevent a backtrack which would break
+                        # (this can't happen in the current code, but is
+                        # a subtle problem in practise, so this line could
+                        # save us some debugging later)
+                        ignore_esc = False
+
+                    # if we want to add the (invalid) escape sequence to the
+                    # TermView verbatim, we'll need to backtrack as well as well
+                    if ignore_esc:
+                        it.backtrack()
+
+
             # at the end of input, flush if we aren't already
             if flush_until == None and it.empty():
                 flush_until = it.pos + 1