Reinstate 'r' and 'history' as preset aliases for interactive ksh

Following a community discussion, it became clear that 'r' is
particularly problematic as a regular builtin, as the name can and
does conflict with at least one legit external command by that
name. There was a consensus against removing it altogether and
letting users set the alias in their login scripts. However,
aliases are easier to bypass, remove or rename than builtins are.
My compromise is to reinstate 'r' as a preset alias on interactive
shells only, along with 'history', as was done in 17f81ebe before
they were converted to builtins in 03224ae3. So this reintroduces
the notion of predefined aliases to ksh 93u+m, but only for
interactive shells that are not initialised in POSIX mode.

src/cmd/ksh93/Makefile,
src/cmd/ksh93/Mamfile,
src/cmd/ksh93/include/shtable.h,
src/cmd/ksh93/data/aliases.c:
- Restore aliases.c containing shtab_aliases[], a table specifying
  the preset aliases.

src/cmd/ksh93/include/shtable.h,
src/cmd/ksh93/sh/init.c:
- Rename inittree() to sh_inittree() and make it extern, because we
  need to use it in main.c (sh_main()).

src/cmd/ksh93/sh/main.c: sh_main():
- Init preset aliases from shtab_aliases[] only if the shell is
  interactive and not in POSIX mode.

src/cmd/ksh93/bltins/typeset.c,
src/cmd/ksh93/tests/alias.sh:
- unall(): When unsetting an alias, pass on the NV_NOFREE attribute
  to nv_delete() to avoid an erroneous attempt to free a preset
  alias from read-only memory. See: 5d50f825

src/cmd/ksh93/data/builtins.c:
- Remove "history" and "r" entries from shtab_builtins[].
- Revert changes to inline fc/hist docs in sh_opthist[].

src/cmd/ksh93/bltins/hist.c: b_hist():
- Remove handling for 'history' and 'r' as builtins.

src/cmd/ksh93/sh.1:
- Update accordingly.

Resolves: https://github.com/ksh93/ksh/issues/125

NEWS

@@ -17,6 +17,11 @@ Any uppercase BUG_* names are modernish shell bug IDs.
      b. 'command' can now stop the shell from exiting if a command that it
 	invokes tries to modify a readonly variable (fixing BUG_CMDSPEXIT).
 
+- The 'history' (== 'hist -l') and 'r' (== 'hist -s') interactive shell
+  history commands have reverted to preset aliases and are now only loaded if
+  the shell is interactive and not initialised in POSIX mode. This avoids
+  unneeded conflicts with external commands by these names, particularly 'r'.
+
 2020-09-09:
 
 - Fixed BUG_LOOPRET2 and related bugs. The 'exit' and 'return' commands without

src/cmd/ksh93/Makefile

@@ -145,7 +145,7 @@ end
 $(SH) :: sh.1 pmain.c $(LIBS_req)
 
 DATAFILES = limits.c msg.c strdata.c testops.c keywords.c options.c \
-                 signals.c builtins.c variables.c lexstates.c
+                 signals.c aliases.c builtins.c variables.c lexstates.c
 
 shell$(RELEASE) $(VERSION) id=shell :LIBRARY: shell.3 nval.3 alarm.c cd_pwd.c cflow.c deparse.c \
 	enum.c getopts.c hist.c misc.c print.c read.c sleep.c trap.c test.c \

src/cmd/ksh93/Mamfile

@@ -1217,6 +1217,16 @@ meta signals.o %.c>%.o data/signals.c signals
 prev data/signals.c
 exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -Iinclude -I${PACKAGE_ast_INCLUDE} -DSHOPT_STATS -DSHOPT_NAMESPACE -DSHOPT_PFSH -DSHOPT_HISTEXPAND -D_BLD_shell -D_API_ast=20100309 -D_PACKAGE_ast -DERROR_CONTEXT_T=Error_context_t -DSHOPT_FIXEDARRAY -DSHOPT_ESH -DSHOPT_MULTIBYTE -c data/signals.c
 done signals.o generated
+make aliases.o
+make data/aliases.c
+prev FEATURE/dynamic implicit
+prev FEATURE/options implicit
+prev include/defs.h implicit
+done data/aliases.c
+meta aliases.o %.c>%.o data/aliases.c aliases
+prev data/aliases.c
+exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -Iinclude -I${PACKAGE_ast_INCLUDE} -DSHOPT_DYNAMIC -DSHOPT_MULTIBYTE -D_PACKAGE_ast -DSHOPT_PFSH -DSHOPT_STATS -DSHOPT_NAMESPACE -DSHOPT_COSHELL -DSHOPT_HISTEXPAND -D_BLD_shell -D_API_ast=20100309 -DERROR_CONTEXT_T=Error_context_t -DSHOPT_FIXEDARRAY -DSHOPT_ESH -c data/aliases.c
+done aliases.o generated
 make builtins.o
 make data/builtins.c
 prev FEATURE/cmds implicit
@@ -1298,7 +1308,7 @@ prev edit/hexpand.c
 exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -Iinclude -I${PACKAGE_ast_INCLUDE} -DSHOPT_HISTEXPAND -DSHOPT_EDPREDICT -DSHOPT_MULTIBYTE -DKSHELL -DSHOPT_ESH -DSHOPT_VSH -D_PACKAGE_ast -DSHOPT_PFSH -DSHOPT_STATS -DSHOPT_NAMESPACE -D_BLD_shell -D_API_ast=20100309 -DERROR_CONTEXT_T=Error_context_t -DSHOPT_FIXEDARRAY -c edit/hexpand.c
 done hexpand.o generated
 exec - ${AR} rc libshell.a alarm.o cd_pwd.o cflow.o deparse.o enum.o getopts.o hist.o misc.o print.o read.o sleep.o trap.o test.o typeset.o ulimit.o umask.o whence.o main.o nvdisc.o nvtype.o arith.o args.o array.o completion.o defs.o edit.o expand.o regress.o fault.o fcin.o
-exec - ${AR} rc libshell.a history.o init.o io.o jobs.o lex.o macro.o name.o nvtree.o parse.o path.o string.o streval.o subshell.o tdump.o timers.o trestore.o waitevent.o xec.o limits.o msg.o strdata.o testops.o keywords.o options.o signals.o builtins.o variables.o lexstates.o emacs.o vi.o hexpand.o
+exec - ${AR} rc libshell.a history.o init.o io.o jobs.o lex.o macro.o name.o nvtree.o parse.o path.o string.o streval.o subshell.o tdump.o timers.o trestore.o waitevent.o xec.o limits.o msg.o strdata.o testops.o keywords.o options.o signals.o aliases.o builtins.o variables.o lexstates.o emacs.o vi.o hexpand.o
 exec - (ranlib libshell.a) >/dev/null 2>&1 || true
 done libshell.a generated
 bind -lshell

src/cmd/ksh93/bltins/hist.c

@@ -58,13 +58,6 @@ int	b_hist(int argc,char *argv[], Shbltin_t *context)
 	NOT_USED(argc);
 	if(!sh_histinit((void*)shp))
 		errormsg(SH_DICT,ERROR_system(1),e_histopen);
-
-	/* 'history' and 'r' builtins */
-	if(argv[0][0] == 'r')  /* <r> */
-		edit = "-";
-	else if(argv[0][0] == 'h' && argv[0][4] == 'o')  /* hist<o>ry (argv[0][4] is zero when called as 'hist') */
-		lflag = 1;
-
 	hp = shp->gd->hist_ptr;
 	while((flag = optget(argv,sh_opthist))) switch(flag)
 	{

src/cmd/ksh93/bltins/typeset.c

@@ -1311,7 +1311,7 @@ static int unall(int argc, char **argv, register Dt_t *troot, Shell_t* shp)
 			}
 			/* The alias has been unset by call to _nv_unset, remove it from the tree */
 			else if(troot==shp->alias_tree)
-				nv_delete(np,troot,0);
+				nv_delete(np,troot,nv_isattr(np,NV_NOFREE));
 #if 0
 			/* causes unsetting local variable to expose global */
 			else if(shp->var_tree==troot && shp->var_tree!=shp->var_base && nv_search((char*)np,shp->var_tree,HASH_BUCKET|HASH_NOSCOPE))

src/cmd/ksh93/data/aliases.c

@@ -0,0 +1,35 @@
+/***********************************************************************
+*                                                                      *
+*               This software is part of the ast package               *
+*          Copyright (c) 1982-2012 AT&T Intellectual Property          *
+*                      and is licensed under the                       *
+*                 Eclipse Public License, Version 1.0                  *
+*                    by AT&T Intellectual Property                     *
+*                                                                      *
+*                A copy of the License is available at                 *
+*          http://www.eclipse.org/org/documents/epl-v10.html           *
+*         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *
+*                                                                      *
+*              Information and Software Systems Research               *
+*                            AT&T Research                             *
+*                           Florham Park NJ                            *
+*                                                                      *
+*                  David Korn <dgk@research.att.com>                   *
+*                                                                      *
+***********************************************************************/
+#pragma prototyped
+#include	"defs.h"
+#include	<signal.h>
+#include	"FEATURE/options"
+#include	"FEATURE/dynamic"
+
+/*
+ * Table of built-in aliases for interactive shells.
+ */
+
+const struct shtable2 shtab_aliases[] =
+{
+	"history",	NV_NOFREE,		"hist -l",
+	"r",		NV_NOFREE,		"hist -s",
+	"",		0,			(char*)0
+};

src/cmd/ksh93/data/builtins.c

@@ -90,8 +90,6 @@ const struct shtable3 shtab_builtins[] =
 	"exit",		NV_BLTIN|BLT_ENV|BLT_SPC,	bltin(return),
 	"fc",		NV_BLTIN|BLT_ENV|BLT_EXIT,	bltin(hist),
 	"hist",		NV_BLTIN|BLT_ENV|BLT_EXIT,	bltin(hist),
-	"history",	NV_BLTIN|BLT_ENV|BLT_EXIT,	bltin(hist),
-	"r",		NV_BLTIN|BLT_ENV|BLT_EXIT,	bltin(hist),
 	"readonly",	NV_BLTIN|BLT_ENV|BLT_SPC|BLT_DCL,bltin(readonly),
 	"shift",	NV_BLTIN|BLT_ENV|BLT_SPC,	bltin(shift),
 	"trap",		NV_BLTIN|BLT_ENV|BLT_SPC,	bltin(trap),
@@ -925,15 +923,11 @@ const char sh_opthash[] =
 ;
 
 const char sh_opthist[]	= 
-"[-1cn?@(#)$Id: hist (AT&T Research/ksh93) 2020-07-16 $\n]"
+"[-1cn?@(#)$Id: hist (AT&T Research) 2000-04-02 $\n]"
 USAGE_LICENSE
-"[+NAME?fc, hist, history, r - process command history list]"
+"[+NAME?\f?\f - process command history list]"
-"[+DESCRIPTION?\bhist\b lists, edits, or re-executes commands  "
+"[+DESCRIPTION?\b\f?\f\b lists, edits, or re-executes, commands  "
 	"previously entered into the current shell environment.]"
-"[+?The following command equivalents exist: "
-	"\bfc\b is \bhist\b; "
-	"\bhistory\b is \bhist -l\b (list history); "
-	"and \br\b is \bhist -s\b (reexecute command).]"
 "[+?The command history list references commands by number. The first number "
 	"in the list is selected arbitrarily.  The relationship of a number "
 	"to its command does not change during a login session.  When the "
@@ -941,11 +935,11 @@ USAGE_LICENSE
 	"maintains the ordering.]"
 "[+?When commands are edited (when the \b-l\b option is not specified), the "
 	"resulting lines will be entered at the end of the history list and "
-	"then reexecuted by the current shell.  The \bhist\b command that "
+	"then reexecuted by the current shell.  The \b\f?\f\b command that "
 	"caused the editing will not be entered into the history list.  If the "
 	"editor returns a non-zero exit status, this will suppress the "
 	"entry into the history list and the command reexecution.  Command "
-	"line variable assignments and redirections affect both the \bhist\b "
+	"line variable assignments and redirections affect both the \f?\f "
 	"command and the commands that are reexecuted.]"
 "[+?\afirst\a and \alast\a define the range of commands. \afirst\a and "
 		"\alast\a can be one of the following:]{"

src/cmd/ksh93/include/shtable.h

@@ -55,10 +55,12 @@ extern const Shtable_t		shtab_testops[];
 extern const Shtable_t		shtab_options[];
 extern const Shtable_t		shtab_attributes[];
 extern const struct shtable2	shtab_variables[];
+extern const struct shtable2	shtab_aliases[];
 extern const struct shtable2	shtab_signals[];
 extern const struct shtable3	shtab_builtins[];
 extern const Shtable_t		shtab_reserved[];
 extern const Shtable_t		*sh_locate(const char*, const Shtable_t*, int);
 extern int			sh_lookopt(const char*, int*);
+extern Dt_t			*sh_inittree(Shell_t*, const struct shtable2*);
 
 #endif /* SH_TABLE_H */

src/cmd/ksh93/sh.1

@@ -782,6 +782,20 @@ the
 .B alias
 definition command has to be executed before
 the command which references the alias is read.
+.PP
+The following aliases are automatically preset
+when the shell is invoked as an interactive shell,
+unless invoked in POSIX compliance mode
+(see
+.I Invocation\^
+below).
+Preset aliases can be unset or redefined.
+.RS 20
+.PD 0
+.TP
+.B "history=\(fmhist \-l\(fm"
+.TP
+.B "r=\(fmhist \-s\(fm"
 .PD
 .RE
 .SS Tilde Substitution.
@@ -4370,9 +4384,9 @@ to re-execute the command.
 In this case a substitution parameter of the form
 \f2old\fP\f3=\fP\f2new\fP
 can be used to modify the command before execution.
-For example, with the builtin
+For example, with the preset alias
 .BR r ,
-which is functionally equivalent to
+which is aliased to
 .BR "\(fmhist \-s\(fm" ,
 typing
 `\f3r bad=good c\fP'
@@ -6239,11 +6253,6 @@ to start
 .I num
 commands back.
 .TP
-\f3history\fP \*(OK \f3\-N\fP \f2num\^\fP \*(CK \*(OK \f3\-nr\^\fP \*(CK \*(OK \f2first\^\fP \*(OK \f2last\^\fP \*(CK \*(CK
-Lists commands in the history file.
-The same as
-.BR hist\ \-l .
-.TP
 \(dd \f3integer\fP \f2vname\fP\*(OK\f3=\fP\f2value\^\fP\*(CK .\|.\|.
 Declares each \f2vname\fP to be a long integer number.
 The same as
@@ -6659,11 +6668,6 @@ or
 on the command line
 determines which method is used.
 .TP
-\f3r\fP \*(OK \f2old\fP\f3\=\fP\f2new\^\fP \*(CK \*(OK \f2command\^\fP \*(CK
-Reexecutes a command in the history file.
-The same as
-.BR hist\ \-s .
-.TP
 \f3read\fP \*(OK \f3\-ACSprsv\^\fP \*(CK \*(OK \f3\-d\fP \f2delim \^\fP\*(CK \*(OK \f3\-n\fP \f2n \^\fP\*(CK \*(OK \*(OK \f3\-N\fP \f2n \^\fP\*(CK \*(OK \f3\-t\fP \f2timeout \^\fP\*(CK \*(OK \f3\-u\fP \f2unit \^\fP\*(CK \*(OK \f2vname\f3?\f2prompt\^\f1 \*(CK \*(OK \f2vname\^\fP .\|.\|. \*(CK
 The shell input mechanism.
 One line is read and
@@ -7059,6 +7063,7 @@ disables passing exported variables' attributes (such as integer or readonly) to
 causes file descriptors > 2 to be left open when invoking another program,
 makes the \fB<>\fR redirection operator default to standard input,
 causes the \fBcommand\fR utility to disable declaration command properties of any declaration commands it invokes,
+skips the initialization of preset aliases upon invoking an interactive shell,
 disables a hack that makes \fBtest -t\fR (\fB[ -t ]\fR) equivalent to \fBtest -t 1\fR (\fB[ -t 1 ]\fR),
 enables octal numbers in \fBlet\fR shell arithmetic (see \fBletoctal\fR), and
 disables the \fB&>\fR redirection shorthand.

src/cmd/ksh93/sh/init.c

@@ -201,7 +201,6 @@ static int		lctype;
 static int		nbltins;
 static void		env_init(Shell_t*,int);
 static Init_t		*nv_init(Shell_t*);
-static Dt_t		*inittree(Shell_t*,const struct shtable2*);
 static int		shlvl;
 
 #ifdef _WINIX
@@ -1709,7 +1708,7 @@ static Init_t *nv_init(Shell_t *shp)
 	shp->nvfun.last = (char*)shp;
 	shp->nvfun.nofree = 1;
 	ip->sh = shp;
-	shp->var_base = shp->var_tree = inittree(shp,shtab_variables);
+	shp->var_base = shp->var_tree = sh_inittree(shp,shtab_variables);
 	SHLVL->nvalue.ip = &shlvl;
 	ip->IFS_init.hdr.disc = &IFS_disc;
 	ip->PATH_init.disc = &RESTRICTED_disc;
@@ -1800,7 +1799,7 @@ static Init_t *nv_init(Shell_t *shp)
 	/* set up the seconds clock */
 	shp->alias_tree = dtopen(&_Nvdisc,Dtoset);
 	shp->track_tree = dtopen(&_Nvdisc,Dtset);
-	shp->bltin_tree = inittree(shp,(const struct shtable2*)shtab_builtins);
+	shp->bltin_tree = sh_inittree(shp,(const struct shtable2*)shtab_builtins);
 	shp->fun_tree = dtopen(&_Nvdisc,Dtoset);
 	dtview(shp->fun_tree,shp->bltin_tree);
 	nv_mount(DOTSHNOD, "type", shp->typedict=dtopen(&_Nvdisc,Dtoset));
@@ -1823,7 +1822,7 @@ static Init_t *nv_init(Shell_t *shp)
  * initialize name-value pairs
  */
 
-static Dt_t *inittree(Shell_t *shp,const struct shtable2 *name_vals)
+Dt_t *sh_inittree(Shell_t *shp,const struct shtable2 *name_vals)
 {
 	register Namval_t *np;
 	register const struct shtable2 *tp;

src/cmd/ksh93/sh/main.c

@@ -175,6 +175,12 @@ int sh_main(int ac, char *av[], Shinit_f userinit)
 		{
 			sh_onoption(SH_BGNICE);
 			sh_onoption(SH_RC);
+			if(!sh_isoption(SH_POSIX))
+			{
+				/* preset aliases for interactive non-POSIX ksh */
+				dtclose(shp->alias_tree);
+				shp->alias_tree = sh_inittree(shp,shtab_aliases);
+			}
 		}
 #if SHOPT_REMOTE
 		/*

src/cmd/ksh93/tests/alias.sh

@@ -109,5 +109,9 @@ alias foo=bar
 unalias foo
 unalias foo && err_exit 'unalias should return non-zero when a previously set alias is unaliased twice'
 
+# Removing a preset alias should work without an error from free(3)
+err=$(set +x; { "$SHELL" -i -c 'unalias history'; } 2>&1) && [[ -z $err ]] \
+|| err_exit "removing a preset alias does not work (got $(printf %q "$err"))"
+
 # ======
 exit $((Errors<125?Errors:125))