fix: check func names against reserved words (reubeno#978)

Author: reubeno

brush-parser/src/parser/peg.rs

@@ -412,8 +412,14 @@ peg::parser! {
             }
 
         // N.B. Non-sh extensions allows use of the 'function' word to indicate a function definition.
+        // N.B. Without the 'function' keyword, reserved words cannot be used as function names
+        // (bash rejects e.g. `for (){ :; }`). With the 'function' keyword, reserved words are
+        // allowed as function names (bash accepts e.g. `function for { :; }`).
         rule function_definition() -> ast::FunctionDefinition =
-            specific_word("function")? fname:fname() body:function_parens_and_body() {
+            specific_word("function") fname:fname() body:function_parens_and_body() {
+                ast::FunctionDefinition { fname, body }
+            } /
+            fname:non_reserved_fname() body:function_parens_and_body() {
                 ast::FunctionDefinition { fname, body }
             } /
             specific_word("function") fname:fname() linebreak() body:function_body() {
@@ -433,6 +439,9 @@ peg::parser! {
             // TODO(parser): Find a way to make this still work without requiring this targeted exception.
             w:[Token::Word(word, l) if !word.ends_with('=')] { ast::Word::with_location(word, l) }
 
+        rule non_reserved_fname() -> ast::Word =
+            !reserved_word() w:fname() { w }
+
         rule brace_group() -> ast::BraceGroupCommand =
             start:specific_word("{") list:compound_list() end:specific_word("}") {
                 let loc = SourceSpan::within(start.location(), end.location());

brush-shell/tests/cases/compat/functions.yaml

@@ -120,6 +120,23 @@ cases:
       .
       echo "Call result: $?"
 
+  - name: "Reserved words cannot be used as function names without function keyword"
+    ignore_stderr: true
+    stdin: |
+      for (){ :; }
+      echo "exit: $?"
+
+  - name: "Reserved words can be used as function names with function keyword"
+    stdin: |
+      function for { echo "custom for"; }
+      for x in 1; do echo "normal for: $x"; done
+
+  - name: "Reserved words can be used as function names with function keyword and parens"
+    stdin: |
+      function while() { echo "custom while"; }
+      while false; do echo "nope"; done
+      echo "done"
+
   - name: "Functions shadowing builtins (POSIX mode)"
     ignore_stderr: true
     stdin: |