Text Escaping

[justinpombrio]

Desired Behavior

In a JSON string:

• " inserts a quote, displayed as ", printed as \", treated as a single char in text navigation.
• \ opens a menu, \n inserts a newline, displayed as \n, printed as \n, treated as a single char in text navigation.
• \\ inserts a backslash, displayed as ⫽, represented as \\, printed as \\, treated as a single char in text navigation.

Data Structures

• Each texty construct has a replacement table (one table may be shared by multiple constructs):
  - A string entry has a src and display string, saying that occurrences of src in source text should be treated as a single character, and displayed as display.
  - A regex entry has a src Regex and a display template. The template can use $n to refer to the regex's n'th capture group. Behaves like the (potentially infinite) set of string replacements that stands for.
  - A ban list gives a set of characters that may start escape sequences and cannot be entered on their own.
• Each Text has:
  • A source string, and an index into it.
  • An optional display string and an index into it. If None, it's implied to be identical to the source string.

Code

• To navigate right, check if there's a source pattern in the replacement table for this construct. If so, skip that many bytes in the source string and a number of bytes equal to the size of the replacement in the display string.
• To navigate left, do the same but checking if something in the replacement table matches on the left. This is annoying for Regexes: each Regex will need a compiled version that starts with $ and one that ends with ^.
• To delete, do the same as navigating left, but modify the string to remove the matches.
• To insert a single character, call Text.insert_char(), which errors if the character is in the ban list.
• To insert an escape sequence, call Text.insert_escape_sequence(), which errors if the sequence does not match something in the replacement table. If it does match, it inserts the src&display matches into the src&display strings. (And sets the display string to Some if it was None.)
• Text.as_str() becomes Text.as_source_str() and Text.as_display_str(). If the display string is None, as_display_str() references the source string (as they're implied to be equal).
• unwrap_text() returns as_source_str() or as_display_str() depending on the mode.
• path_to_root() also returns either as_source_str() or as_display_str() depending on the mode. I think.