Re: jsonapi: scary new warnings with LTO enabled - Mailing list pgsql-hackers

I noticed some new warnings from buildfarm member chafer,
which I'm able to reproduce locally on a Fedora 41 box
by building with "meson setup build -Db_lto=true":

ninja: Entering directory `build'
[1515/2472] Linking target src/interfaces/libpq/libpq.so.5.18
In function 'freeJsonLexContext',
    inlined from 'freeJsonLexContext' at ../src/common/jsonapi.c:688:1,
    inlined from 'handle_oauth_sasl_error' at ../src/interfaces/libpq/fe-auth-oauth.c:547:2:
../src/common/jsonapi.c:723:17: warning: 'free' called on unallocated object 'lex' [-Wfree-nonheap-object]
  723 |                 FREE(lex);
      |                 ^
../src/interfaces/libpq/fe-auth-oauth.c: In function 'handle_oauth_sasl_error':
../src/interfaces/libpq/fe-auth-oauth.c:479:24: note: declared here
  479 |         JsonLexContext lex = {0};
      |                        ^
[2407/2472] Linking target src/test/modules/test_json_parser/test_json_parser_incremental_shlib
In function 'freeJsonLexContext',
    inlined from 'freeJsonLexContext' at ../src/common/jsonapi.c:688:1,
    inlined from 'main' at ../src/test/modules/test_json_parser/test_json_parser_incremental.c:198:2:
../src/common/jsonapi.c:723:17: warning: 'free' called on unallocated object 'lex' [-Wfree-nonheap-object]
  723 |                 FREE(lex);
      |                 ^
../src/test/modules/test_json_parser/test_json_parser_incremental.c: In function 'main':
../src/test/modules/test_json_parser/test_json_parser_incremental.c:87:24: note: declared here
   87 |         JsonLexContext lex;
      |                        ^
[2426/2472] Linking target src/test/modules/test_json_parser/test_json_parser_incremental
In function 'pg_free',
    inlined from 'pfree' at ../src/common/fe_memutils.c:135:2,
    inlined from 'freeJsonLexContext' at ../src/common/jsonapi.c:723:3,
    inlined from 'freeJsonLexContext' at ../src/common/jsonapi.c:688:1,
    inlined from 'main' at ../src/test/modules/test_json_parser/test_json_parser_incremental.c:198:2:
../src/common/fe_memutils.c:107:9: warning: 'free' called on unallocated object 'lex' [-Wfree-nonheap-object]
  107 |         free(ptr);
      |         ^
../src/test/modules/test_json_parser/test_json_parser_incremental.c: In function 'main':
../src/test/modules/test_json_parser/test_json_parser_incremental.c:87:24: note: declared here
   87 |         JsonLexContext lex;
      |                        ^

AFAICT there is no actual bug here: the FREE() call is reached only if
the JSONLEX_FREE_STRUCT flag is set, which it should not be for these
call sites.