[Python] Fixes for string escapes, placeholders, replacements (sublimehq#4366)

* [Python] Scope placeholders in raw strings

This commit includes `string-placeholders` context to raw strings
as all of them can be used as format-strings in e.g. `R"Hello %s" % R'World'`.

* [Python] Reorder context includes

This commit reorders include statements to reduce syntax cache size.

* [Python] Fix string replacements

This commit...

1. moves string-replacement includes before includes of normal escapes
   to make sure special `{{` and `\{{` escape patterns take precedence.

2. removes string-replacement includes from b-strings as those don't
   support format methods such as `b"{0}".format(b"invalid")` and string
   format placeholders are not scoped as well.

3. adds string-replacement includes to plain raw strings, as those can be
   used in format strings and string format placeholders have been added,
   before.

   Notes:
   - raw SQL strings already include them
   - raw RegExp strings need more work to prevent ambiguities with braced
     quantifiers such as `{1}`, hence don't include them at the moment.

* [Python] Drop unicode escapes from raw-strings

This commit removes `escaped-unicode-chars` context includes from all raw
string content contexts as each of them returns e.g. `\u2020` unchanged.

* [Python] Merge escaped string replacement braces

As a result of reordering string-replacement contexts, it turns out f-strings
and normal string-replacements sharing same brace escaping rules.

* [Python] Move and extend some f-string tests

This commit...
1. moves various tests to group f-string tests.
2. adds tests for escape sequences and placeholders in all sorts of f-strings.

* [Python] Add tests to verify recent changes

This commit adds tests for all sorts of (except f-) strings to verify escape
sequences, placeholders and string replacements being applied as expected.

* [Python] Restrict known regexp escape sequences

This commit overrides `known_char_escape` variable in python's regexp syntax to

1. scope all `\c` sequences illegal, even when followed by numbers,
   as python's `re` and `regex` modules don't support it.
2. remove explicit patterns `\\[tnrfae]` as those are handled by default
   escape pattern `\.`.

Author: deathaxe

Python/Embeddings/RegExp (for Python).sublime-syntax

@@ -8,6 +8,9 @@ hidden: true
 extends: Packages/Regular Expressions/RegExp (Basic).sublime-syntax
 
 variables:
+  # escapes
+  known_char_escape: \\(?:[0-7]{3}|x\{\h{1,7}\}|x\h\h)
+
   # modifiers
   activate_x_mode: (?:\?[imsLua]*x[ixmsLua]*(?:-[imsLua]+)?)
   deactivate_x_mode: (?:\?[imsLua]*-[imsLua]*x[imxsLua]*)

Python/Python.sublime-syntax

@@ -2806,8 +2806,9 @@ contexts:
 
   triple-double-quoted-plain-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
+    - include: triple-double-quoted-string-replacements
     - include: escaped-raw-quotes
-    - include: escaped-unicode-chars
 
   triple-double-quoted-raw-u-string:
     # Triple-quoted raw string, unicode or not, will detect SQL, otherwise regex
@@ -2841,7 +2842,7 @@ contexts:
 
   triple-double-quoted-regexp-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-unicode-chars
+    - include: string-placeholders
 
   triple-double-quoted-sql-raw-u-string-body:
     - meta_include_prototype: false
@@ -2855,10 +2856,9 @@ contexts:
 
   triple-double-quoted-sql-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-raw-quotes
-    - include: escaped-unicode-chars
     - include: string-placeholders
     - include: triple-double-quoted-string-replacements
+    - include: escaped-raw-quotes
 
   triple-double-quoted-b-string:
     # Triple-quoted string, bytes, no syntax embedding
@@ -2877,9 +2877,8 @@ contexts:
   triple-double-quoted-b-string-content:
     - include: string-prototype
     - include: string-continuations
-    - include: escaped-chars
     - include: string-placeholders
-    - include: triple-double-quoted-string-replacements
+    - include: escaped-chars
 
   triple-double-quoted-f-string:
     # Triple-quoted f-string or t-string
@@ -2942,10 +2941,10 @@ contexts:
   triple-double-quoted-u-string-content:
     - include: string-prototype
     - include: string-continuations
-    - include: escaped-unicode-chars
-    - include: escaped-chars
     - include: string-placeholders
     - include: triple-double-quoted-string-replacements
+    - include: escaped-unicode-chars
+    - include: escaped-chars
 
   triple-double-quoted-string-replacements:
     - include: escaped-string-braces
@@ -2989,7 +2988,7 @@ contexts:
       fail: triple-double-quoted-string-replacement
 
   triple-double-quoted-f-string-replacements:
-    - include: escaped-f-string-braces
+    - include: escaped-string-braces
     - include: invalid-f-string-replacements
     - match: \{
       scope: punctuation.section.interpolation.begin.python
@@ -3158,6 +3157,8 @@ contexts:
 
   double-quoted-plain-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
+    - include: double-quoted-string-replacements
     - include: escaped-raw-quotes
 
   double-quoted-raw-u-string:
@@ -3193,6 +3194,7 @@ contexts:
 
   double-quoted-regexp-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
 
   double-quoted-sql-raw-u-string-body:
     - meta_include_prototype: false
@@ -3206,9 +3208,9 @@ contexts:
 
   double-quoted-sql-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-raw-quotes
     - include: string-placeholders
     - include: double-quoted-string-replacements
+    - include: escaped-raw-quotes
 
   double-quoted-b-string:
     # Single-line string, bytes
@@ -3226,9 +3228,8 @@ contexts:
 
   double-quoted-b-string-content:
     - include: string-prototype
-    - include: escaped-chars
     - include: string-placeholders
-    - include: double-quoted-string-replacements
+    - include: escaped-chars
 
   double-quoted-f-string:
     # Single-line f-string or t-string
@@ -3289,10 +3290,10 @@ contexts:
 
   double-quoted-u-string-content:
     - include: string-prototype
-    - include: escaped-unicode-chars
-    - include: escaped-chars
     - include: string-placeholders
     - include: double-quoted-string-replacements
+    - include: escaped-unicode-chars
+    - include: escaped-chars
 
   double-quoted-string-replacements:
     - include: escaped-string-braces
@@ -3336,7 +3337,7 @@ contexts:
       fail: double-quoted-string-replacement
 
   double-quoted-f-string-replacements:
-    - include: escaped-f-string-braces
+    - include: escaped-string-braces
     - include: invalid-f-string-replacements
     - match: \{
       scope: punctuation.section.interpolation.begin.python
@@ -3496,6 +3497,8 @@ contexts:
 
   triple-single-quoted-plain-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
+    - include: triple-single-quoted-string-replacements
     - include: escaped-raw-quotes
 
   triple-single-quoted-raw-u-string:
@@ -3530,7 +3533,7 @@ contexts:
 
   triple-single-quoted-regexp-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-unicode-chars
+    - include: string-placeholders
 
   triple-single-quoted-sql-raw-u-string-body:
     - meta_include_prototype: false
@@ -3544,10 +3547,9 @@ contexts:
 
   triple-single-quoted-sql-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-raw-quotes
-    - include: escaped-unicode-chars
     - include: string-placeholders
     - include: triple-single-quoted-string-replacements
+    - include: escaped-raw-quotes
 
   triple-single-quoted-b-string:
     # Triple-quoted string, bytes, no syntax embedding
@@ -3566,9 +3568,8 @@ contexts:
   triple-single-quoted-b-string-content:
     - include: string-prototype
     - include: string-continuations
-    - include: escaped-chars
     - include: string-placeholders
-    - include: triple-single-quoted-string-replacements
+    - include: escaped-chars
 
   triple-single-quoted-f-string:
     # Triple-quoted f-string or t-string
@@ -3631,10 +3632,10 @@ contexts:
   triple-single-quoted-u-string-content:
     - include: string-prototype
     - include: string-continuations
-    - include: escaped-unicode-chars
-    - include: escaped-chars
     - include: string-placeholders
     - include: triple-single-quoted-string-replacements
+    - include: escaped-unicode-chars
+    - include: escaped-chars
 
   triple-single-quoted-string-replacements:
     - include: escaped-string-braces
@@ -3678,7 +3679,7 @@ contexts:
       fail: triple-single-quoted-string-replacement
 
   triple-single-quoted-f-string-replacements:
-    - include: escaped-f-string-braces
+    - include: escaped-string-braces
     - include: invalid-f-string-replacements
     - match: \{
       scope: punctuation.section.interpolation.begin.python
@@ -3806,6 +3807,8 @@ contexts:
 
   single-quoted-plain-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
+    - include: single-quoted-string-replacements
     - include: escaped-raw-quotes
 
   single-quoted-raw-u-string:
@@ -3841,6 +3844,7 @@ contexts:
 
   single-quoted-regexp-raw-u-string-content:
     - include: string-prototype
+    - include: string-placeholders
 
   single-quoted-sql-raw-u-string-body:
     - meta_include_prototype: false
@@ -3854,9 +3858,9 @@ contexts:
 
   single-quoted-sql-raw-u-string-content:
     - include: string-prototype
-    - include: escaped-raw-quotes
     - include: string-placeholders
     - include: single-quoted-string-replacements
+    - include: escaped-raw-quotes
 
   single-quoted-plain-raw-f-string:
     # Single-line raw f-string
@@ -3915,9 +3919,8 @@ contexts:
 
   single-quoted-b-string-content:
     - include: string-prototype
-    - include: escaped-chars
     - include: string-placeholders
-    - include: single-quoted-string-replacements
+    - include: escaped-chars
 
   single-quoted-f-string:
     # Single-line f-string or t-string
@@ -3978,10 +3981,10 @@ contexts:
 
   single-quoted-u-string-content:
     - include: string-prototype
-    - include: escaped-unicode-chars
-    - include: escaped-chars
     - include: string-placeholders
     - include: single-quoted-string-replacements
+    - include: escaped-unicode-chars
+    - include: escaped-chars
 
   single-quoted-string-replacements:
     - include: escaped-string-braces
@@ -4025,7 +4028,7 @@ contexts:
       fail: single-quoted-string-replacement
 
   single-quoted-f-string-replacements:
-    - include: escaped-f-string-braces
+    - include: escaped-string-braces
     - include: invalid-f-string-replacements
     - match: \{
       scope: punctuation.section.interpolation.begin.python
@@ -4099,7 +4102,7 @@ contexts:
     # but don't scope them as escapes as they are treated literal
     - match: \\[\\'"]
 
-  escaped-f-string-braces:
+  escaped-string-braces:
     # https://peps.python.org/pep-0498
     # https://peps.python.org/pep-0701
     # https://docs.python.org/3.6/reference/lexical_analysis.html#f-strings
@@ -4108,10 +4111,6 @@ contexts:
       captures:
         1: invalid.deprecated.character.escape.python
 
-  escaped-string-braces:
-    - match: \{\{|\}\}
-      scope: constant.character.escape.python
-
   string-placeholders:
     - match: |- # printf style
         (?x)