ast, parser, fio: fix six PVS-Studio findings

[borisbat]

Triage of a PVS-Studio sweep over the vendored daScript copy: ~80 warnings, 6 real findings, all fixed here. Everything else classified as false positives (invariant-guarded derefs the parser guarantees, gc_node-tracked "leaks", deliberate hopeless-clear memsets, union aliasing PVS can't model, flex-generated boilerplate).

Fixes

1. isFullySealed copy-paste (ast_typedecl.cpp) — null-checked secondType but re-tested firstType, so a sealed key type masked an unsealed value type (e.g. a table with sealed key and still-auto value), letting typeinfo offsetof fold prematurely. Pinned by a new doctest (tests-cpp/small/test_fully_sealed.cpp).
2. Bitfield-constant null deref (ast_infer_type.cpp) — the "bitfield constant ... is not initialized" error branch fell through to found->init->clone(). Added the missing return; only reachable via macro-side flag manipulation (the grammar always sets the initializer).
3. Silent ambiguous-variable failure (ast_infer_type.cpp) — else { if (verbose) error(...) } made the terse "too many matching variables" diagnostic dead code, so non-verbose compiles reported nothing for an ambiguous global. Also folded the mirror always-true if (verbose) on the "can't locate variable" path.
4. Dangling updateAliasMapCallback (ast_infer_type_function.cpp, 2 sites) — early returns left program->updateAliasMapCallback holding a lambda capturing dead stack frames by reference; a later das-side update_alias_map call (typeinfo macro) would write through them. The third site already cleared the callback before its early return — copied that pattern.
5. Lexer line-directive OOB write (ds_lexer.lpp + ds2_lexer.lpp) — the file name in #row,col,"file"# was parsed with sscanf %s, which stops at whitespace: a file name containing a space made strlen(lFile)-2 underflow into a wild out-of-bounds write. Both lexers now take the quote-bounded span directly (also un-breaks paths with spaces and paths longer than 255 chars). Generated lexer sources regenerated.
6. context guard asymmetry (module_builtin_fio.cpp) — register_dynamic_module deref'd context unguarded on its first error path while both sibling error paths guard with if (context); harmonized (a null context is passed internally today, Quiet-only).

Validation

• preflight --full: 16 passed, 0 failed (lint skipped — no .das changes): cpp-syntax full sweep, das2rst + sphinx latex/html + pdflatex, tests-cpp, interp + JIT + AOT suites, sequence smoke
• full das suite: 11036 tests, 0 failed
• ctest: 64/64 incl. the new isFullySealed regression test
• lexer probed by hand: #5,1,"probe b.das"# (space in name) now lexes, resolves, and runs; plain directives unchanged

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a handful of confirmed PVS-Studio findings in daScript’s core compiler/runtime components (AST/type inference, dynamic module loading, and both lexers), and adds a C++ regression test to lock in the isFullySealed behavior.

Changes:

• Fix TypeDecl::isFullySealed to correctly validate secondType (plus new doctest regression coverage).
• Fix two inference/diagnostic issues in ast_infer_type.cpp (missing return in a bitfield-constant error path; make ambiguous-variable diagnostics non-silent).
• Harden lexer line-directive filename extraction to handle whitespace safely (and regenerate lexer outputs), plus guard a Context* deref in register_dynamic_module.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests-cpp/small/test_fully_sealed.cpp	Adds regression coverage ensuring isFullySealed checks secondType independently.
src/ast/ast_typedecl.cpp	Fixes copy-paste bug: secondType now calls secondType->isFullySealed.
src/ast/ast_infer_type.cpp	Adds missing early return on bitfield-constant init error; ensures ambiguous/missing variable errors are emitted consistently.
src/ast/ast_infer_type_function.cpp	Clears program->updateAliasMapCallback on early-return paths to avoid dangling callbacks.
src/builtin/module_builtin_fio.cpp	Guards context before emitting/throwing on dynamic module load failure.
src/parser/ds_lexer.lpp	Fixes line-directive filename parsing to use quote-bounded span (supports spaces; avoids OOB write).
src/parser/ds_lexer.cpp	Regenerated lexer output reflecting the line-directive parsing fix.
src/parser/ds2_lexer.lpp	Same line-directive parsing fix for ds2 lexer.
src/parser/ds2_lexer.cpp	Regenerated ds2 lexer output reflecting the line-directive parsing fix.
src/parser/lex.yy.h	Regenerated header line markers (line directives shifted due to lexer regeneration).
src/parser/lex2.yy.h	Regenerated header line markers (line directives shifted due to lexer regeneration).

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