THRIFT-6076: Fix GCC 14 LTO false-positive stringop-overflow in compiler generators

[bigjust]

Summary

GCC 14 with LTO (-flto=auto -ffat-lto-objects) produces false-positive -Werror=stringop-overflow / -Werror=stringop-overread errors at link time when chained std::string() + "literal" + "literal" expressions in the compiler generator sources are inlined across translation units. The code is correct; this is a GCC 14 LTO inter-procedural analysis limitation.

Tracked in: https://issues.apache.org/jira/browse/THRIFT-6076

Affected functions

File	Function
t_javame_generator.cc	java_type_imports(), java_thrift_imports()
t_haxe_generator.cc	haxe_type_imports(), haxe_thrift_imports()
t_js_generator.cc	autogen_comment()
t_ocaml_generator.cc	ocaml_autogen_comment()
t_perl_generator.cc	autogen_comment()
t_erl_generator.cc	erl_autogen_comment()
t_go_generator.cc	go_autogen_comment()
t_delphi_generator.cc	autogen_comment()
t_rb_generator.cc	rb_autogen_comment()
t_xsd_generator.cc	xml_autogen_comment()

Fix

Replace chained operator+ on temporaries with:

• Adjacent string literal concatenation for pure-literal returns (resolved entirely at compile time, no temporary objects, no operator+ at all).
• Single operator+ call for returns that embed THRIFT_VERSION, with compile-time-concatenated literal strings on both sides of the variable — this gives GCC LTO a correctly-sized left operand to analyse.

Example (pure literals — t_javame_generator.cc)

// Before
return string() + "import java.util.Hashtable;\n" + "import java.util.Vector;\n"
       + "import java.util.Enumeration;\n\n";

// After
return "import java.util.Hashtable;\n"
       "import java.util.Vector;\n"
       "import java.util.Enumeration;\n\n";

Example (contains THRIFT_VERSION — t_js_generator.cc)

// Before
return std::string("//\n") + "// Autogenerated by Thrift Compiler (" + THRIFT_VERSION + ")\n"
       + "//\n" + "// DO NOT EDIT UNLESS YOU ARE SURE THAT YOU KNOW WHAT YOU ARE DOING\n"
       + "//\n";

// After
return "//\n"
       "// Autogenerated by Thrift Compiler (" + THRIFT_VERSION + ")\n"
       "//\n"
       "// DO NOT EDIT UNLESS YOU ARE SURE THAT YOU KNOW WHAT YOU ARE DOING\n"
       "//\n";

[Copilot]

Pull request overview

This PR updates several C++ compiler generator helpers to avoid GCC 14 LTO false-positive -Werror=stringop-overflow/-overread diagnostics by eliminating chained std::string temporary concatenations in returned string constants.

Changes:

• Replaced std::string() + "..." + "..." patterns with adjacent string-literal concatenation for pure-literal returns.
• Refactored autogenerated-header comment construction in multiple generators to reduce/avoid operator+ chains (notably where THRIFT_VERSION is embedded).
• Simplified a few returns that previously forced std::string temporaries (e.g., Go generator autogen comment).

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
compiler/cpp/src/thrift/generate/t_xsd_generator.cc	Refactors XML autogen comment string construction.
compiler/cpp/src/thrift/generate/t_rb_generator.cc	Refactors Ruby autogen comment string construction.
compiler/cpp/src/thrift/generate/t_perl_generator.cc	Refactors Perl autogen comment string construction.
compiler/cpp/src/thrift/generate/t_ocaml_generator.cc	Refactors OCaml autogen comment string construction.
compiler/cpp/src/thrift/generate/t_js_generator.cc	Refactors JS autogen comment string construction.
compiler/cpp/src/thrift/generate/t_javame_generator.cc	Converts JavaME import lists to adjacent-literal concatenation.
compiler/cpp/src/thrift/generate/t_haxe_generator.cc	Converts Haxe import lists to adjacent-literal concatenation.
compiler/cpp/src/thrift/generate/t_go_generator.cc	Simplifies Go autogen comment return expression.
compiler/cpp/src/thrift/generate/t_erl_generator.cc	Refactors Erlang autogen comment string construction.
compiler/cpp/src/thrift/generate/t_delphi_generator.cc	Refactors Delphi autogen comment string construction.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

[Jens-G]

Code review

No verified issues found. Checked for bugs and CLAUDE.md compliance; all candidate findings were refuted by adversarial verification.

🤖 Generated with Claude Code

[Jens-G]

Something is sill broken here.

[Copilot]

Pull request overview

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