A deeply nested Perl call chain f(f(f(...))) overflowed the stack while
parsing on small-stack platforms: tree-sitter's GLR parser recurses once
per nesting level in stack_node_add_link (vendored ts_runtime/src/stack.c)
merging the ambiguous parse-stack heads that Perl's f(...) grammar produces.
The overflow happens during ts_parser_parse, before any LSP walk runs, so
the CBM_LSP_PERL_MAX_WALK_DEPTH guards can never fire. This crashed
test-windows (CLANG64) with an AddressSanitizer stack-overflow and hung
test-unix (ubuntu-24.04-arm) to a 4h timeout on lsp_perl_deep_expression_no_crash.
Add cbm_source_nesting_exceeds(): an O(n) early-exit bracket-depth scan, and
skip extraction (clean has_error, zero edges) for Perl input whose nesting
exceeds CBM_PERL_MAX_PARSE_NESTING (128) before it reaches tree-sitter.
Scoped to Perl because only its ambiguous call grammar drives the GLR
recursion to the nesting depth; C/Java/Python parse the same shape with a
single stack head. 128 is ~10x above any real Perl nesting and well below
the depth where the parser overflows a 1MB stack.
Correct the lsp_perl_deep_expression_no_crash comment to describe the actual
mechanism (parser recursion, not the LSP walk).
Signed-off-by: Shane McCarron <shane.mccarron@corvexconnect.com>
Shane McCarron
89aecfd2fc