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Add some cscope support to mg. From Sunil Nimmagadda.  Due to some
structural limitations in mg, mg doesn't behave exactly the same as
emacs cscope (see the README) but is still very usable.

man page bits reviewed by jmc@, otherwise tested and reviewed by
myself.

/*
 * Copyright (c) 2011 Sunil Nimmagadda <sunil@sunilnimmagadda.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/queue.h>
#include <sys/stat.h>
#include <sys/tree.h>
#include <sys/types.h>

#include <ctype.h>
#include <err.h>
#include <stdlib.h>
#include <string.h>
#include <util.h>

#include "def.h"

struct ctag;

static int               addctag(char *);
static int               atbow(void);
void                     closetags(void);
static int               ctagcmp(struct ctag *, struct ctag *);
static int               loadbuffer(char *);
static int               loadtags(const char *);
static int               pushtag(char *);
static int               searchpat(char *);
static struct ctag       *searchtag(char *);
static char              *strip(char *, size_t);
static void              unloadtags(void);

#define DEFAULTFN "tags"

char *tagsfn = NULL;
int  loaded  = FALSE;

/* ctags(1) entries are parsed and maintained in a tree. */
struct ctag {
	RB_ENTRY(ctag) entry;
	char *tag;
	char *fname;
	char *pat;
};
RB_HEAD(tagtree, ctag) tags = RB_INITIALIZER(&tags);
RB_GENERATE(tagtree, ctag, entry, ctagcmp);

struct tagpos {
	SLIST_ENTRY(tagpos) entry;
	int    doto;
	int    dotline;
	char   *bname;
};
SLIST_HEAD(tagstack, tagpos) shead = SLIST_HEAD_INITIALIZER(shead);

int
ctagcmp(struct ctag *s, struct ctag *t)
{
	return strcmp(s->tag, t->tag);
}

/*
 * Record the filename that contain tags to be used while loading them
 * on first use. If a filename is already recorded, ask user to retain
 * already loaded tags (if any) and unload them if user chooses not to.
 */
/* ARGSUSED */
int
tagsvisit(int f, int n)
{
	char fname[NFILEN], *bufp, *temp;
	struct stat sb;
	
	if (getbufcwd(fname, sizeof(fname)) == FALSE)
		fname[0] = '\0';
	
	if (strlcat(fname, DEFAULTFN, sizeof(fname)) >= sizeof(fname)) {
		ewprintf("Filename too long");
		return (FALSE);
	}
	
	bufp = eread("visit tags table (default %s): ", fname,
	    NFILEN, EFFILE | EFCR | EFNEW | EFDEF, DEFAULTFN);

	if (stat(bufp, &sb) == -1) {
		ewprintf("stat: %s", strerror(errno));
		return (FALSE);
	} else if (S_ISREG(sb.st_mode) == 0) {
		ewprintf("Not a regular file");
		return (FALSE);
	} else if (access(bufp, R_OK) == -1) {
		ewprintf("Cannot access file %s", bufp);
		return (FALSE);
	}
	
	if (tagsfn == NULL) {
		if (bufp == NULL)
			return (ABORT);
		else if (bufp[0] == '\0') {
			if ((tagsfn = strdup(fname)) == NULL) {
				ewprintf("Out of memory");
				return (FALSE);
			}
		} else {
			/* bufp points to local variable, so duplicate. */
			if ((tagsfn = strdup(bufp)) == NULL) {
				ewprintf("Out of memory");
				return (FALSE);
			}
		}
	} else {
		if ((temp = strdup(bufp)) == NULL) {
			ewprintf("Out of memory");
			return (FALSE);
		}
		free(tagsfn);
		tagsfn = temp;
		if (eyorn("Keep current list of tags table also") == FALSE) {
			ewprintf("Starting a new list of tags table");
			unloadtags();
		}
		loaded = FALSE;
	}
	return (TRUE);
}

/*
 * Ask user for a tag while treating word at dot as default. Visit tags
 * file if not yet done, load tags and jump to definition of the tag.
 */
int
findtag(int f, int n)
{
	char utok[MAX_TOKEN], dtok[MAX_TOKEN];
	char *tok, *bufp;
	int  ret;

	if (curtoken(f, n, dtok) == FALSE)
		return (FALSE);
	
	bufp = eread("Find tag (default %s) ", utok, MAX_TOKEN,
	    EFNUL | EFNEW, dtok);

	if (bufp == NULL)
		return (ABORT);
	else if	(bufp[0] == '\0')
		tok = dtok;
	else
		tok = utok;
	
	if (tok[0] == '\0') {
		ewprintf("There is no default tag");
		return (FALSE);
	}
	
	if (tagsfn == NULL)
		if ((ret = tagsvisit(f, n)) != TRUE)
			return (ret);
	if (!loaded) {
		if (loadtags(tagsfn) == FALSE) {
			free(tagsfn);
			tagsfn = NULL;
			return (FALSE);
		}
		loaded = TRUE;
	}
	return pushtag(tok);
}

/*
 * Free tags tree.
 */
void
unloadtags(void)
{
	struct ctag *var, *nxt;
	
	for (var = RB_MIN(tagtree, &tags); var != NULL; var = nxt) {
		nxt = RB_NEXT(tagtree, &tags, var);
		RB_REMOVE(tagtree, &tags, var);
		/* line parsed with fparseln needs to be freed */
		free(var->tag);
		free(var);
	}
}

/*
 * Lookup tag passed in tree and if found, push current location and 
 * buffername onto stack, load the file with tag definition into a new
 * buffer and position dot at the pattern.
 */
/*ARGSUSED */
int
pushtag(char *tok)
{
	struct ctag *res;
	struct tagpos *s;
	char bname[NFILEN];
	int doto, dotline;
	
	if ((res = searchtag(tok)) == NULL)
		return (FALSE);
		
	doto = curwp->w_doto;
	dotline = curwp->w_dotline;
	/* record absolute filenames. Fixes issues when mg's cwd is not the
	 * same as buffer's directory.
	 */
	if (strlcpy(bname, curbp->b_cwd, sizeof(bname)) >= sizeof(bname)) {
		    ewprintf("filename too long");
		    return (FALSE);
	}
	if (strlcat(bname, curbp->b_bname, sizeof(bname)) >= sizeof(bname)) {
		    ewprintf("filename too long");
		    return (FALSE);
	}	

	if (loadbuffer(res->fname) == FALSE)
		return (FALSE);
	
	if (searchpat(res->pat) == TRUE) {
		if ((s = malloc(sizeof(struct tagpos))) == NULL) {
			ewprintf("Out of memory");
			return (FALSE);
		}
		if ((s->bname = strdup(bname)) == NULL) {
			ewprintf("Out of memory");
			return (FALSE);
		}
		s->doto = doto;
		s->dotline = dotline;
		SLIST_INSERT_HEAD(&shead, s, entry);
		return (TRUE);
	} else {
		ewprintf("%s: pattern not found", res->tag);
		return (FALSE);
	}
	/* NOTREACHED */
	return (FALSE);
}

/*
 * If tag stack is not empty pop stack and jump to recorded buffer, dot.
 */
/* ARGSUSED */
int
poptag(int f, int n)
{
	struct line *dotp;
	struct tagpos *s;
	
	if (SLIST_EMPTY(&shead)) {
		ewprintf("No previous location for find-tag invocation");
		return (FALSE);
	}
	s = SLIST_FIRST(&shead);
	SLIST_REMOVE_HEAD(&shead, entry);
	if (loadbuffer(s->bname) == FALSE)
		return (FALSE);
	curwp->w_dotline = s->dotline;
	curwp->w_doto = s->doto;
	
	/* storing of dotp in tagpos wouldn't work out in cases when
	 * that buffer is killed by user(dangling pointer). Explicitly
	 * traverse till dotline for correct handling. 
	 */
	dotp = curwp->w_bufp->b_headp;
	while (s->dotline--)
		dotp = dotp->l_fp;
	
	curwp->w_dotp = dotp;
	free(s->bname);
	free(s);
	return (TRUE);
}

/*
 * Parse the tags file and construct the tags tree. Remove escape 
 * characters while parsing the file.
 */
int
loadtags(const char *fn)
{
	char *l;
	FILE *fd;
	
	if ((fd = fopen(fn, "r")) == NULL) {
		ewprintf("Unable to open tags file: %s", fn);
		return (FALSE);
	}
	while ((l = fparseln(fd, NULL, NULL, "\\\\\0",
	    FPARSELN_UNESCCONT | FPARSELN_UNESCREST)) != NULL) {
		if (addctag(l) == FALSE) {
			fclose(fd);
			return (FALSE);
		}
	}
	fclose(fd);
	return (TRUE);
}

/*
 * Cleanup and destroy tree and stack.
 */
void
closetags(void)
{
	struct tagpos *s;	
	
	while (!SLIST_EMPTY(&shead)) {
		s = SLIST_FIRST(&shead);
		SLIST_REMOVE_HEAD(&shead, entry);
		free(s->bname);
		free(s);
	}
	unloadtags();
	free(tagsfn);
}

/*
 * Strip away any special characters in pattern.
 * The pattern in ctags isn't a true regular expression. Its of the form
 * /^xxx$/ or ?^xxx$? and in some cases the "$" would be missing. Strip 
 * the leading and trailing special characters so the pattern matching
 * would be a simple string compare. Escape character is taken care by 
 * fparseln.
 */
char *
strip(char *s, size_t len)
{
	/* first strip trailing special chars */	
	s[len - 1] = '\0';
	if (s[len - 2] == '$')
		s[len - 2] = '\0';
	
	/* then strip leading special chars */
	s++;
	if (*s == '^')
		s++;
	
	return s;
}

/*
 * tags line is of the format "<tag>\t<filename>\t<pattern>". Split them
 * by replacing '\t' with '\0'. This wouldn't alter the size of malloc'ed
 * l, and can be freed during cleanup.
 */
int
addctag(char *l)
{
	struct ctag *t;
	
	if ((t = malloc(sizeof(struct ctag))) == NULL) {
		ewprintf("Out of memory");
		return (FALSE);
	}
	t->tag = l;
	if ((l = strchr(l, '\t')) == NULL)
		goto cleanup;
	*l++ = '\0';
	t->fname = l;
	if ((l = strchr(l, '\t')) == NULL)
		goto cleanup;
	*l++ = '\0';
	if (*l == '\0')
		goto cleanup;
	t->pat = strip(l, strlen(l));
	RB_INSERT(tagtree, &tags, t);
	return (TRUE);
cleanup:
	free(t);
	free(l);
	return (TRUE);
}

/*
 * Search through each line of buffer for pattern.
 */
int
searchpat(char *pat)
{
	struct line *lp;
	int dotline;
	size_t plen;

	plen = strlen(pat);
	dotline = 1;
	lp = lforw(curbp->b_headp);
	while (lp != curbp->b_headp) {
		if (ltext(lp) != NULL && plen <= llength(lp) &&
		    (strncmp(pat, ltext(lp), plen) == 0)) {
			curwp->w_doto = 0;
			curwp->w_dotp = lp;
			curwp->w_dotline = dotline;
			return (TRUE);
		} else {
			lp = lforw(lp);
			dotline++;
		}
	}
	return (FALSE);
}

/*
 * Return TRUE if dot is at beginning of a word or at beginning 
 * of line, else FALSE.
 */
int
atbow(void)
{
	if (curwp->w_doto == 0)
		return (TRUE);
	if (ISWORD(curwp->w_dotp->l_text[curwp->w_doto]) &&
	    !ISWORD(curwp->w_dotp->l_text[curwp->w_doto - 1]))
	    	return (TRUE);
	return (FALSE);
}

/*
 * Extract the word at dot without changing dot position.
 */
int
curtoken(int f, int n, char *token)
{
	struct line *odotp;
	int odoto, tdoto, odotline, size, r;
	char c;
	
	/* Underscore character is to be treated as "inword" while
	 * processing tokens unlike mg's default word traversal. Save
	 * and restore it's cinfo value so that tag matching works for
	 * identifier with underscore.
	 */
	c = cinfo['_'];
	cinfo['_'] = _MG_W;
	
	odotp = curwp->w_dotp;
	odoto = curwp->w_doto;
	odotline = curwp->w_dotline;
	
	/* Move backword unless we are at the beginning of a word or at
	 * beginning of line.
	 */
	if (!atbow())
		if ((r = backword(f, n)) == FALSE)
			goto cleanup;
		
	tdoto = curwp->w_doto;

	if ((r = forwword(f, n)) == FALSE)
		goto cleanup;
	
	/* strip away leading whitespace if any like emacs. */
	while (ltext(curwp->w_dotp) && 
	    isspace(curwp->w_dotp->l_text[tdoto]))
		tdoto++;

	size = curwp->w_doto - tdoto;
	if (size <= 0 || size >= MAX_TOKEN || 
	    ltext(curwp->w_dotp) == NULL) {
		r = FALSE;
		goto cleanup;
	}    
	strncpy(token, ltext(curwp->w_dotp) + tdoto, size);
	token[size] = '\0';
	r = TRUE;
	
cleanup:
	cinfo['_'] = c;
	curwp->w_dotp = odotp;
	curwp->w_doto = odoto;
	curwp->w_dotline = odotline;
	return (r);
}

/*
 * Search tagstree for a given token.
 */
struct ctag *
searchtag(char *tok)
{
	struct ctag t, *res;

	t.tag = tok;
	if ((res = RB_FIND(tagtree, &tags, &t)) == NULL) {
		ewprintf("No tag containing %s", tok);
		return (NULL);
	}
	return res;
}

/*
 * This is equivalent to filevisit from file.c.
 * Look around to see if we can find the file in another buffer; if we
 * can't find it, create a new buffer, read in the text, and switch to
 * the new buffer. *scratch*, *grep*, *compile* needs to be handled 
 * differently from other buffers which have "filenames".
 */
int
loadbuffer(char *bname)
{
	struct buffer *bufp;
	char *adjf;

	/* check for special buffers which begin with '*' */
	if (bname[0] == '*') {
		if ((bufp = bfind(bname, FALSE)) != NULL) {
			curbp = bufp;
			return (showbuffer(bufp, curwp, WFFULL));
		} else {
			return (FALSE);
		}
	} else {	
		if ((adjf = adjustname(bname, TRUE)) == NULL)
			return (FALSE);
		if ((bufp = findbuffer(adjf)) == NULL)
			return (FALSE);
	}
	curbp = bufp;
	if (showbuffer(bufp, curwp, WFFULL) != TRUE)
		return (FALSE);
	if (bufp->b_fname[0] == '\0') {
		if (readin(adjf) != TRUE) {
			killbuffer(bufp);
			return (FALSE);
		}
	}
	return (TRUE);
}