`JOIN WITH <alias> TO <file> [FIELDS <list>] [FOR <expr>]` becomes a
preprocessor rewrite to a new RTL primitive __dbJoin. Cartesian
product of the current ("master") workarea and the named "detail"
alias, filtered by the FOR expression.
Output structure:
* No FIELDS clause: master's fields followed by detail's, dropping
any detail-side name that clashes with master.
* FIELDS list: one column per name in declaration order, resolved
against master first then detail.
Same shape as harbour-core/src/rdd/dbjoin.prg. Five-specific
simplifications: alias->name in FIELDS not yet supported (bare
names with master-precedence lookup); RDD/codepage args dropped
since Five only has DBFNTX.
Note for callers: don't name a workarea `M` or `MEMVAR` — both are
Harbour-reserved memvar aliases, so `M->field` and `MEMVAR->field`
always go through the memory-variable namespace, not the workarea.
This is gengo behavior matching Harbour, not new in this commit.
Parser cleanup: JOIN removed from the IDENT-statement no-op switch.
Gates green:
go test ./... : PASS
FiveSql2 SQL:1999 : 43/43
Harbour compat : 56/56
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>