I don't believe you.
Here, I inserted a subtle bug in this function, can you find it?
int widget_grid(lv*target,grid x,grid_val*value){
if(x.show==show_none)return 0; lv*hfnt=FONT_BODY; int hsize=x.headers?font_h(hfnt)+5:0; if(x.size.h<=(50+hsize)||x.size.w<16)x.scrollbar=0;
lv*fnt=x.font?x.font:FONT_MONO; int os=value->scroll, or=value->row, oc=value->col, files=x.headers==2; if(files||x.size.h<=hsize)x.headers=0;
int _bg=dgeti(value->table,lmistr("_bg")),_fg=dgeti(value->table,lmistr("_fg")),_hideby=dgeti(value->table,lmistr("_hideby"));
lv*pv=NULL,*vp=NULL;if(target!=NULL&&_hideby!=-1)grid_pv(target,&pv,&vp);int nr=pv?pv->c: value->table->n;
#define grid_cell_at(col,row) (value->table->lv[col]->lv[permuted_row(row)])
int nc=MIN(256,value->table->c), rh=font_h(fnt)+(x.lines?5:3), fcol=!in_layer()?13:x.show==show_invert?32:1, bcol=x.show==show_invert?1:32;
int fk=strlen(x.format); rect b=x.size;
int sel=in_layer()&&x.show!=show_none&&wid.active==wid.count;
if(in_layer()&&dover(b)&&(ev.md||ev.mu||ev.drag)){if(!sel&&wid.gv)grid_exit(); wid.active=wid.count,sel=1;}
if(sel&&in_layer()&&!over(b)&&ev.md){sel=0;wid.active=-1;grid_exit();}
if(sel){if(wid.fv)field_exit();wid.ingrid=1,wid.g=x,wid.gv=value,wid.gt=target;}
if(x.show!=show_transparent)draw_rect(b,bcol);
rect bh={b.x,b.y,b.w,x.headers?font_h(hfnt)+5:0}; int nrd=MIN(nr,((b.h-bh.h+1)/rh)), scrollmax=nr-nrd;
rect bb=scrollbar((rect){b.x,b.y+(x.headers?bh.h-1:0),b.w,b.h-(x.headers?bh.h-1:0)},scrollmax,1,nrd,&value->scroll,x.scrollbar,x.show==show_invert);
draw_box(x.lines?b:(rect){b.x,bb.y,b.w,b.h-(bb.y-b.y)},0,sel?13:fcol);
char*pal=patterns_pal(ifield(deck,"patterns"));
if(x.lines)draw_rect(bh,fcol);if(nc<=0)draw_textc(inset(bb,1),"(no data)",hfnt,fcol);
int cw[256];for(int z=0;z<nc;z++)cw[z]=z>=x.widths[0]?-1:x.widths[1+z];
if(_bg!=-1)cw[_bg]=0;if(_fg!=-1)cw[_fg]=0;if(_hideby!=-1)cw[_hideby]=0;
int hwt=0;for(int z=0;z<x.widths[0];z++)hwt+=cw[z];
int nwt=0;for(int z=0;z<nc ;z++)nwt+=cw[z]==-1;
for(int z=x.widths[0];z<nc ;z++)cw[z]=cw[z]==-1?(bb.w-hwt)/nwt:0;
if(!cf.sv)cf=str_new();
#define rowh(n) inset((rect){bb.x+1,bb.y+rh*n+2,bb.w-2,rh-3},x.lines?0:-1)
#define rowb(n) (rect){bb.x,bb.y+rh*n,bb.w,rh}
int clicked=0,rsel=0,hrow=-1,hcol=-1;
for(int y=0;y<nrd;y++){
if(_bg!=-1){
int p=CLAMP(0,ln(grid_cell_at(_bg,y+value->scroll)),255);
if(p){rect t=rowb(y);if(y==0)t.y+=1,t.h-=1; draw_rect(t,p);}
}
int ra=in_layer()&&over(bb)&&over(rowb(y));rect cbox={0};
if(ra&&x.bycell){for(int z=0;z<nc;z++){rect cell=grid_cell(x,value,bb,(pair){z,y},cw);if(over(cell))hcol=z,cbox=grid_hcell(x,z,cell);}}
if(ra&&(ev.md||ev.drag)){rsel=1,hrow=y+value->scroll;draw_rect(x.bycell?cbox:rowh(y),fcol);}
if(ra&&ev.mu)clicked=1,value->row=permuted_row(y+value->scroll),value->col=hcol;
if(ra&&!ev.drag)uicursor=cursor_point;
}int rr=display_row(value->row)-value->scroll;
if(!rsel&&rr>=0&&rr<nrd&&(x.bycell?value->col>=0&&value->col<nc:1)){
hrow=display_row(value->row),hcol=value->col;
if(x.bycell&&value->col>=0){draw_rect(grid_hcell(x,value->col,grid_cell(x,value,bb,(pair){value->col,rr},cw)),fcol);}
else{draw_rect(rowh(rr),fcol);}
}
int drawncol=0;for(int z=0,cols=0,cx=0;z<nc&&cx+cw[cols]<=bb.w;z++,cols++){
rect hs=(rect){bh.x+4+cx,bh.y+1,cw[cols]-5,bh.h-2};
if(hs.w<=0)continue; // suppressed column
if(x.headers){
int oa=target&&in_layer()&&over(hs)&&((ev.drag||ev.mu)?dover(hs):1)&&!wid.col_drag;
int dp=oa&&(ev.md||ev.drag);if(dp)draw_rect(hs,x.lines?bcol:fcol);
draw_textc(hs,value->table->kv[z]->sv,hfnt,x.lines^dp?bcol:fcol);
if(oa&&!ev.drag)uicursor=cursor_point;
if(oa&&ev.mu){msg.target_order=target,msg.arg_order=value->table->kv[z];}
}
if(drawncol&&x.lines)draw_invert(pal,(rect){hs.x-3,b.y+1,1,b.h-2});cx+=cw[cols];drawncol=1;
for(int y=0;y<nrd;y++){
int ccol=y+value->scroll==hrow&&(x.bycell?cols==hcol :1)?bcol: _fg==-1?fcol: CLAMP(0,ln(grid_cell_at(_fg,y+value->scroll)),255);
rect cell={hs.x-3,bb.y+rh*y+1,hs.w+5,rh-1}; lv*v=grid_cell_at(z,y+value->scroll);
cf.c=0;format_type_simple(&cf,v,z>fk?'s':x.format[z]=='L'?'s':x.format[z]);str_term(&cf);
rect ib=box_center(cell,image_size(ICONS[0]));pair ip={ib.x,ib.y};
rect oc=frame.clip; frame.clip=box_intersect(cell,frame.clip);
if (z<fk&&x.format[z]=='I'){int i=MAX(0,MIN(8,ln(v)));if(i<8)draw_icon(ip,ICONS[i],ccol);}
else if(z<fk&&x.format[z]=='B'){if(lb(v))draw_icon(ip,ICONS[icon_chek],ccol);}
else if(z<fk&&(x.format[z]=='t'||x.format[z]=='T')){
rect rr={hs.x+1,bb.y+rh*y,hs.w-2,rh}; // display rich text:
pair t=layout_richtext(deck,rtext_cast(v),fnt,align_left,rr.w);
rect r={rr.x,rr.y+ceil(t.y<rr.h?(rr.h-t.y)/2.0:0),rr.w,rr.h};
lv*alink=NULL;if(x.format[z]=='T'&&in_layer()&&(ev.md||ev.drag||ev.mu))for(int z=0;z<layout_count;z++){
glyph_box g=layout[z];if(g.pos.w<1)continue; // skip squashed spaces/newlines
if(g.pos.y+g.pos.h<0||g.pos.y>r.h)continue; g.pos.x+=r.x, g.pos.y+=r.y; // coarse clip
if(lis(g.arg)&&g.arg->c&&dover(g.pos)&&over(g.pos)){
if(ev.md||ev.drag){alink=g.arg;break;}
if(ev.mu){msg.target_link=target,msg.arg_link=g.arg;break;}
}
}
draw_text_rich_raw(r,ccol,0,alink);
}
else{
rect r={hs.x+1,bb.y+rh*y,hs.w-2,rh}; // right-align numeric columns:
if(z<fk&&strchr("fcCihH",x.format[z])){draw_textr(r,cf.sv,fnt,ccol);}else{draw_text_fit(r,cf.sv,fnt,ccol);}
}
frame.clip=oc;
if(!x.locked&&sel&& ((ev.dclick&&over(cell)) || (ev.action&&x.bycell&&z==value->col&&y+value->scroll==display_row(value->row)))){
char f=z<fk?x.format[z]:'s';pair tc=(pair){z,y+value->scroll},tpc=(pair){tc.x,permuted_row(tc.y)};
if (f=='I'||f=='L'||f=='T'){} // no editing allowed
else if(f=='B'||f=='b'){grid_edit_cell(tpc,ls(lmn(!lb(v))));} // toggle
else{
ms.pending_grid_cell_rich=f=='t';
wid.pending_grid_edit=1,ms.pending_grid_cell=grid_cell(x,value,bb,(pair){tc.x,tc.y-value->scroll},cw);
ms.pending_grid_cell.y-=1,ms.pending_grid_cell.w+=1,ms.pending_grid_cell.h+=2;
ms.cell=tpc;ms.text=(field_val){f=='t'?rtext_cast(v):rtext_cast(lmcstr(cf.sv)),0};
}
}
}
}
if(x.lines)for(int y=1;y<nrd;y++)draw_hline(bb.x,bb.x+bb.w,bb.y+rh*y,fcol);
if(!x.locked&&in_layer()&&target)for(int z=0,cx=bh.x;z<nc;cx+=cw[z],z++){
if(cw[z]==0)continue;
rect h={cx+cw[z]-1,bh.y,5,bh.h};if(h.x+h.w>b.x+b.w)break;
if(over(h))draw_vline(h.x+2,h.y,h.y+h.h,13);
if(ev.md&&dover(h)){wid.col_drag=1,wid.col_num=z,wid.col_orig=cw[z];}
if(sel&&wid.col_drag&&wid.col_num==z&&ev.drag){
int s=MIN(MAX(10,wid.col_orig+(ev.pos.x-ev.dpos.x)),bb.w-10),i=z;uicursor=cursor_drag;
GEN(r,MAX(x.widths[0],i+1))lmn(i==z?s:cw[z]);iwrite(target,lmistr("widths"),r),mark_dirty();
}
}
if(target&&os!=value->scroll)iwrite(target,lmistr("scroll"),lmn(value->scroll)),mark_dirty();
if(target&&or!=value->row)iwrite(target,lmistr("row"),lmn(value->row)),mark_dirty();
if(target&&oc!=value->col)iwrite(target,lmistr("col"),lmn(value->col)),mark_dirty();
if(target&&clicked)msg.target_click=target,msg.arg_click=(fpair){0,value->row};
if(in_widgets())wid.count++;
return files?((clicked&&ev.dclick)||(sel&&ev.action)): clicked;
}