build.ninja

srcdir = .
builddir = .

cc = gcc
cflags = -Wall -Wextra -O2 -g
cppflags = 

rule cc
  depfile = $out.d
  command = $cc -MMD -MF $out.d $cflags $cppflags-c $in -o $out

build $builddir/hello.o: cc $srcdir/hello.c

build all: phony || $builddir/hello.o

gistfile2.txt

% ninja all
[1/1] gcc -MMD -MF ./hello.o.d -Wall -Wextra -O2 -g -c ./hello.c -o ./hello.o
% ninja all
ninja: error: expected makefile to mention './hello.o', got 'hello.o'
[1]    16941 exit 1     ninja all

hello.c

#include <stdio.h>
int main()
{
  printf("Hello.\n");
  return 0;
}