language: Fix indent suggestions for significant indented languages like Python (#29625)

Closes #26157

This fixes multiple cases where Python indentation breaks:
- [x] Adding a new line after `if`, `try`, etc. correctly indents in
that scope
- [x] Multi-cursor tabs correctly preserve relative indents
- [x] Adding a new line after `else`, `finally`, etc. correctly outdents
them
- [x] Existing Tests

Future Todo: I need to add new tests for all the above cases.

Before/After:

1. Multi-cursor tabs correctly preserve relative indents


https://github.com/user-attachments/assets/08a46ddf-5371-4e26-ae7d-f8aa0b31c4a2

2. Adding a new line after `if`, `try`, etc. correctly indents in that
scope


https://github.com/user-attachments/assets/9affae97-1a50-43c9-9e9f-c1ea3a747813

Release Notes:

- Fixes indentation-related issues involving tab, newline, etc for
Python.

crates/languages/src/python.rs

@@ -1209,7 +1209,7 @@ mod tests {
             append(&mut buffer, "foo(\n1)", cx);
             assert_eq!(
                 buffer.text(),
-                "def a():\n  \n  if a:\n    b()\n  else:\n    foo(\n      1)"
+                "def a():\n  \n  if a:\n    b()\n  else:\n    foo(\n    1)"
             );
 
             // dedent the closing paren if it is shifted to the beginning of the line
@@ -1255,7 +1255,7 @@ mod tests {
 
             // dedent "else" on the line after a closing paren
             append(&mut buffer, "\n  else:\n", cx);
-            assert_eq!(buffer.text(), "if a:\n  b(\n  )\nelse:\n  ");
+            assert_eq!(buffer.text(), "if a:\n  b(\n  )\nelse:\n");
 
             buffer
         });

crates/languages/src/python/config.toml

@@ -27,6 +27,7 @@ brackets = [
 ]
 
 auto_indent_using_last_non_empty_line = false
-increase_indent_pattern = "^[^#].*:\\s*$"
-decrease_indent_pattern = "^\\s*(else|elif|except|finally)\\b.*:"
 debuggers = ["Debugpy"]
+significant_indentation = true
+increase_indent_pattern = "^\\s*(try)\\b.*:"
+decrease_indent_pattern = "^\\s*(else|elif|except|finally)\\b.*:"

crates/languages/src/python/indents.scm

@@ -1,18 +1,43 @@
-(_ "[" "]" @end) @indent
-(_ "{" "}" @end) @indent
-(_ "(" ")" @end) @indent
-
-(try_statement
-    body: (_) @start
-    [(except_clause) (finally_clause)] @end
-    ) @indent
+(function_definition
+  ":" @start
+  body: (block) @indent
+)
 
 (if_statement
-    consequence: (_) @start
-    alternative: (_) @end
-    ) @indent
+  ":" @start
+  consequence: (block) @indent
+  alternative: (_)? @outdent
+)
 
-(_
-    alternative: (elif_clause) @start
-    alternative: (_) @end
-    ) @indent
+(else_clause
+  ":" @start
+  body: (block) @indent
+)
+
+(elif_clause
+  ":" @start
+  consequence: (block) @indent
+)
+
+(for_statement
+  ":" @start
+  body: (block) @indent
+)
+
+(try_statement
+  ":" @start
+  body: (block) @indent
+  (except_clause)? @outdent
+  (else_clause)? @outdent
+  (finally_clause)? @outdent
+)
+
+(except_clause
+  ":" @start
+  (block) @indent
+)
+
+(finally_clause
+  ":" @start
+  (block) @indent
+)