Diffs from patch v5:

* Let "write_name_quoted_relative" support two terminations, they are
  "CQ_NO_TERMINATOR_C_QUOTED" and "CQ_NO_TERMINATOR_AS_IS" (They are
  used to let the function write "name" at a 'c_quoted' way or just
  'as-is', but without print a terminator).
  
* Rename "follow" to "interspace" (Representing whether any further
  output needs an inter-field space).

* Nits fixed.

Many thanks to Junio and Ævar for your help and patient explanation.
I noticed Ævar suggest the solution with using `--format`, but in
this patch, the current approach continues. If this part of code needs
to be improved or we want to support "--format" in "ls-tree" in the
future, I'm more than glad to continue to contribute.

Thanks.

Teng Long (1):
  ls-tree.c: support `--object-only` option for "git-ls-tree"

 Documentation/git-ls-tree.txt |   7 +-
 builtin/ls-tree.c             | 131 ++++++++++++++++++++++++----------
 quote.c                       |   8 +--
 quote.h                       |  19 +++++
 t/t3103-ls-tree-misc.sh       |   8 +++
 t/t3104-ls-tree-oid.sh        |  51 +++++++++++++
 6 files changed, 183 insertions(+), 41 deletions(-)
 create mode 100755 t/t3104-ls-tree-oid.sh

Range-diff against v5:
1:  38d55a878c ! 1:  2e449d1c79 ls-tree.c: support `--object-only` option for "git-ls-tree"
    @@ builtin/ls-tree.c
     -#define LS_SHOW_TREES 4
     -#define LS_NAME_ONLY 8
     -#define LS_SHOW_SIZE 16
    -+#define LS_TREE_ONLY 1 << 1
    -+#define LS_SHOW_TREES 1 << 2
    -+#define LS_NAME_ONLY 1 << 3
    -+#define LS_SHOW_SIZE 1 << 4
    -+#define LS_OBJECT_ONLY 1 << 5
    ++#define LS_TREE_ONLY (1 << 1)
    ++#define LS_SHOW_TREES (1 << 2)
    ++#define LS_NAME_ONLY (1 << 3)
    ++#define LS_SHOW_SIZE (1 << 4)
    ++#define LS_OBJECT_ONLY (1 << 5)
      static int abbrev;
      static int ls_options;
      static struct pathspec pathspec;
      static int chomp_prefix;
      static const char *ls_tree_prefix;
    -+static unsigned int shown_bits = 0;
    -+#define SHOW_DEFAULT 29 /* 11101 size is not shown to output by default */
    -+#define SHOW_MODE 1 << 4
    -+#define SHOW_TYPE 1 << 3
    -+#define SHOW_OBJECT_NAME 1 << 2
    -+#define SHOW_SIZE 1 << 1
    ++static unsigned int shown_bits;
     +#define SHOW_FILE_NAME 1
    ++#define SHOW_SIZE (1 << 1)
    ++#define SHOW_OBJECT_NAME (1 << 2)
    ++#define SHOW_TYPE (1 << 3)
    ++#define SHOW_MODE (1 << 4)
    ++#define SHOW_DEFAULT 29 /* 11101 size is not shown to output by default */
      
      static const  char * const ls_tree_usage[] = {
      	N_("git ls-tree [<options>] <tree-ish> [<path>...]"),
    @@ builtin/ls-tree.c
     +	MODE_UNSPECIFIED = 0,
     +	MODE_NAME_ONLY,
     +	MODE_OBJECT_ONLY,
    -+	MODE_LONG
    ++	MODE_LONG,
     +};
     +
     +static int cmdmode = MODE_UNSPECIFIED;
    @@ builtin/ls-tree.c: static int show_tree(const struct object_id *oid, struct strb
      {
      	int retval = 0;
      	int baselen;
    -+	int follow = 0;
    ++	int interspace = 0;
      	const char *type = blob_type;
      
      	if (S_ISGITLINK(mode)) {
    @@ builtin/ls-tree.c: static int show_tree(const struct object_id *oid, struct strb
     -			       find_unique_abbrev(oid, abbrev),
     -			       size_text);
     +	if (shown_bits & SHOW_MODE) {
    -+		printf("%06o",mode);
    -+		follow = 1;
    ++		printf("%06o", mode);
    ++		interspace = 1;
     +	}
     +	if (shown_bits & SHOW_TYPE) {
    -+		printf("%s%s", follow == 1 ? " " : "", type);
    -+		follow = 1;
    ++		printf("%s%s", interspace ? " " : "", type);
    ++		interspace = 1;
     +	}
     +	if (shown_bits & SHOW_OBJECT_NAME) {
    -+		printf("%s%s", follow == 1 ? " " : "",
    ++		printf("%s%s", interspace ? " " : "",
     +		       find_unique_abbrev(oid, abbrev));
     +		if (!(shown_bits ^ SHOW_OBJECT_NAME))
    -+			printf("%c", line_termination);
    -+		follow = 1;
    ++			goto LINE_FINISH;
    ++		interspace = 1;
     +	}
     +	if (shown_bits & SHOW_SIZE) {
     +		char size_text[24];
    @@ builtin/ls-tree.c: static int show_tree(const struct object_id *oid, struct strb
     -			printf("%06o %s %s\t", mode, type,
     -			       find_unique_abbrev(oid, abbrev));
     +			xsnprintf(size_text, sizeof(size_text), "-");
    -+		printf("%s%7s", follow == 1 ? " " : "", size_text);
    -+		follow = 1;
    ++		printf("%s%7s", interspace ? " " : "", size_text);
    ++		interspace = 1;
     +	}
     +	if (shown_bits & SHOW_FILE_NAME) {
    -+		if (follow)
    ++		if (interspace)
     +			printf("\t");
     +		baselen = base->len;
     +		strbuf_addstr(base, pathname);
     +		write_name_quoted_relative(base->buf,
     +					   chomp_prefix ? ls_tree_prefix : NULL,
    -+					   stdout, line_termination);
    ++					   stdout,
    ++					   line_termination
    ++					   ? CQ_NO_TERMINATOR_C_QUOTED
    ++					   : CQ_NO_TERMINATOR_AS_IS);
     +		strbuf_setlen(base, baselen);
      	}
     -	baselen = base->len;
    @@ builtin/ls-tree.c: static int show_tree(const struct object_id *oid, struct strb
     -				   chomp_prefix ? ls_tree_prefix : NULL,
     -				   stdout, line_termination);
     -	strbuf_setlen(base, baselen);
    ++
    ++LINE_FINISH:
    ++	putchar(line_termination);
      	return retval;
      }
      
    @@ builtin/ls-tree.c: int cmd_ls_tree(int argc, const char **argv, const char *pref
      	 * show_recursive() rolls its own matching code and is
      	 * generally ignorant of 'struct pathspec'. The magic mask
     
    + ## quote.c ##
    +@@ quote.c: void quote_two_c_style(struct strbuf *sb, const char *prefix, const char *path,
    + 
    + void write_name_quoted(const char *name, FILE *fp, int terminator)
    + {
    +-	if (terminator) {
    ++	if (0 < terminator || terminator == CQ_NO_TERMINATOR_C_QUOTED)
    + 		quote_c_style(name, NULL, fp, 0);
    +-	} else {
    ++	else
    + 		fputs(name, fp);
    +-	}
    +-	fputc(terminator, fp);
    ++	if (0 <= terminator)
    ++		fputc(terminator, fp);
    + }
    + 
    + void write_name_quoted_relative(const char *name, const char *prefix,
    +
    + ## quote.h ##
    +@@ quote.h: int unquote_c_style(struct strbuf *, const char *quoted, const char **endp);
    + #define CQUOTE_NODQ 01
    + size_t quote_c_style(const char *name, struct strbuf *, FILE *, unsigned);
    + void quote_two_c_style(struct strbuf *, const char *, const char *, unsigned);
    ++/*
    ++ * Write a name, typically a filename, followed by a terminator that
    ++ * separates it from what comes next.
    ++ * When terminator is NUL, the name is given as-is.  Otherwise, the
    ++ * name is c-quoted, suitable for text output.  HT and LF are typical
    ++ * values used for the terminator, but other positive values are possible.
    ++ *
    ++ * In addition to non-negative values two special values in terminator
    ++ * are possible.
    ++ *
    ++ * -1: show the name c-quoted, without adding any terminator.
    ++ * -2: show the name as-is, without adding any terminator.
    ++ */
    ++#define CQ_NO_TERMINATOR_C_QUOTED	(-1)
    ++#define CQ_NO_TERMINATOR_AS_IS		(-2)
    + 
    + void write_name_quoted(const char *name, FILE *, int terminator);
    ++/*
    ++ * Similar to the above, but the name is first made relative to the prefix
    ++ * before being shown.
    ++ */
    + void write_name_quoted_relative(const char *name, const char *prefix,
    + 				FILE *fp, int terminator);
    + 
    +
      ## t/t3103-ls-tree-misc.sh ##
     @@ t/t3103-ls-tree-misc.sh: test_expect_success 'ls-tree fails with non-zero exit code on broken tree' '
      	test_must_fail git ls-tree -r HEAD
-- 
2.33.1.10.g5f17c1a2c1.dirty