# S978: Reserved identifiers should not be defined or declared
id: no-reserved-identifiers
name: Reserved Identifiers Should Not Be Defined
severity: error
category: maintainability
defect_class: correctness
inline_tier: blocking
language: c

message: "identifier {{NAME}} uses a reserved namespace — identifiers beginning with '_' + uppercase or '__' are reserved by the implementation"

description: |
  The C standard reserves all identifiers that begin with an underscore
  followed by an uppercase letter or another underscore. Using them can
  cause conflicts with compiler/runtime internals.

  ✅ FIX: Rename without leading underscore(s)

  ```c
  int my_buffer_size = 1024;  // GOOD
  ```

query: |
  [
    (identifier) @NAME (#match? @NAME "^_[A-Z_]")
    (field_identifier) @NAME (#match? @NAME "^_[A-Z_]")
    (type_identifier) @NAME (#match? @NAME "^_[A-Z_]")
  ]

metavars:
  - NAME

tags:
  - maintainability
  - c
  - bad-practice
  - portability

examples:
  bad: |
    int _MyVar = 1;       // BAD - _ + uppercase
    int __internal = 2;   // BAD - double underscore

  good: |
    int myVar = 1;        // GOOD
    int internal = 2;     // GOOD

has_fix: true
fix_action: rename_identifier