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Fix BUG_KBGPID: $! was not updated under certain conditions
The $! special parameter was not set if a background job (somecommand &) or co-process (somecommand |&) was launched as the only command within a braces block with an attached redirection, for example: { somecommand & } >&2 With the bug, $! was unchanged; now it contains the PID of somecommand. Ref.: att#1357 src/cmd/ksh93/sh/parse.c: item(): - When processing redirections following a compound command, always create a parent node with the TSETIO (I/O redirection) token. Before this commit, if the last command was of type TFORK (and the last command only tested as TFORK if the bg job or coprocess was the only command in a braces block, because the ksh parser optimises away the braces in that case), then the parent node was created with the TFORK token instead. I have no idea what David Korn's intention was with that, but this is clearly very wrong. Creating another TFORK node when parsing the redirection caused sh_exec() in sh/xec.c to execute the redirection in an extra forked, non-background subshell. Since redirections are executed before anything else, this subshell is what then launched the background job between the braces, so $! (a.k.a. shp->bckpid) was updated in that subshell only, and never in the main shell. The extra subshell also prevented the background job from being noticed by job control on interactive shells. So, the fix is simply to remove the broken test for TFORK. src/cmd/ksh93/tests/variables.sh: - Add regression tests for a bg job and a co-process as the only command within a braces block with attached redirection. (cherry picked from commit ffe5df30e69f7b596941a98498014d8e838861f2)
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