For each file name in names, returns the relative path to the file. This relative path does not contain any unnecessary . or .. components, nor any repeated path separators (/).
Justification (trimpath): trimpath can be used to shorten the input strings to compilers/linkers, as well as improve readability to the user. Certain compilers have a maximum number of characters which can be passed into a single invocation of their compiler. In my project, I had a dozen or so -include<search_path> which contained many unnecessary . and .. components, which caused the compiler to overflow the input buffer. While it is unfortunate compilers exist with unreasonably small input buffers, trimpath allowed me to only pass in the minimum number of characters required to successfully compile.
Also, the readability of paths printed to the console is greatly improved by trimpath. I was regularly dealing with paths of the following structure:
-I../../../_make_interface/../../../_make_system/source/_make_implementation/../3rdparty/libs/gtest/include
which would be reduced by trimpath to:
-I../../../../../_make_system/source/3rdparty/libs/gtest/include
abspath could have made these paths longer depending on the depth into the filesystem that the project was being built.
Justification (relpath): Similiar to trimpath, relpath can be used to shorten the input strings to compilers/linkers, as well as improve readability to the user. For example, in my build system, libraries are "published" relative to a known directory, and paths to these libraries are built up for each executable that needs them. Consider an executable foo which links to library bar. If foo and bar exist in a directory name directoryname, then the relative path to library bar would be"
-L../bar
However, the build system generates:
-L../../_make_interface/../directoryname/bar
which relpath reduces back to:
-L../bar
As a note, trimpath would only reduce the path in this case to:
-L../../directoryname/bar
abspath and realpath could potentially create:
-L/home/benjamin.robinson/workspace/xseries/source/directoryname/bar
Code Improvements: I agree with the coding suggestions you have made. I will refactor my submission to incorporate your suggestions, provided Paul agrees the submission is justified. A small note: my implementation is based on abspath from version 3.81 of function.c which did not use IS_ABSOLUTE, ROOT_LEN, IS_PATHSEP, etc... I will refactor my submission to use them, along with your other suggestions, provided it passes the justification gate. And I will further clarify my intent in the code comments where you indicated.
Ben Robinson, Ph.D.
On Mon, May 30, 2011 at 12:23 AM, Eli Zaretskii
<address@hidden> wrote:
> Date: Sun, 29 May 2011 21:45:38 -0700
> From: Ben Robinson <address@hidden>
>
> I am submitting a patch which adds two new functions to GNU Make.
Thanks. Please wait for Paul's word about inclusion of these in
Make. What's below are a few comments based on a first impression
from the code.
> $(trimpath names...)
> For each file name in names, returns a name that does not contain any . or
> .. components, nor any repeated path separators (/).
The part about "." and ".." is inaccurate: the function removes any
redundant "." and "..", but it's not true that the value will never
include these, as your tests clearly show:
> ifneq ($(trimpath ../foo/),../foo)
> $(error )
> endif
> $(relpath names...)
> For each file name in names, returns the relative path to the file.
This doesn't say relative to what. From reading the code I understand
that it's relative to the starting directory (which could be different
from the current directory when a given recipe runs). Why not use
$(CURDIR) instead?
> This
> relative path does not contain any . or .. components, nor any repeated path
> separators (/).
Again, this is inaccurate: periods will still appear when they are
needed.
> These functions contain capabilities which are significantly different from
> the existing abspath and realpath, in that they do not convert what could be
> an extremely short relative path (e.g. ".") into a long absolute path.
> relpath is in fact the inverse of abspath, and adding it would make the set
> of path conversion functions more complete. In addition, trimpath can be
> applied to paths both absolute and relative, and eliminate needless
> characters which can improve readability and performance.
Any use case where adding these functions would be needed?
Completeness is not generally enough to add features.
A few comments on the code, mostly related to Windows portability:
> > if (name[0] == '/') {
> > ++fixed;
> > abspath = 1;
> > }
This is not the GNU style of using braces (here and everywhere else in
the patch).
> > /* A Windows style absolute path */
> > if (name[1] == ':' && name[2] == '/') {
> > fixed += 3;
> > abspath = 1;
> > }
Please use the existing IS_ABSOLUTE and ROOT_LEN macros.
Also, I'm not sure the Windows parts should be compiled on Posix
platforms, since it is possible (although unlikely) to have a file or
directory there named "C:".
> > /* Take only the first path-separator. */
> > if (*start == '/') {
> > ++start;
> > *dest++ = '/';
> > }
Please don't assume the directory separator is always '/', it could be
'\\' on DOS/Windows. Please use IS_PATHSEP instead of literal
slashes.
> > /* Skip sequence of multiple path-separators. */
> > while (*start == '/') {
> > ++start;
> > }
This will defeat UNC "//foo/bar" or "\\\\foo\\bar" file names on
Windows.
> > /* Strip the trailing separator if any. */
> > if (dest > apath && dest[-1] == '/') {
> > /* Unless name is an absolute path resulting in only '/' */
> > if (!(name[0] == '/' && dest == apath + 1)) {
> > --dest;
This does not consider the DOS/Windows case where an absolute file
name does not begin with a slash.
> > /* If the resulting path is empty, return a '.' */
> > if (dest == apath) {
> > *dest++ = '.';
> > }
Same here.
> > /* A unix style absolute path */
> > if (name[0] == '/') {
> > abspath = 1;
> > if (starting_directory[1] == ':' && starting_directory[2] == '/') {
> > /* A Windows system should not get passed a unix style absolute path */
> > return NULL;
What happens if starting_directory is a "//foo/bar" UNC?
> > /* A Windows style absolute path */
> > if (name[1] == ':' && name[2] == '/') {
Again, please use IS_ABSOLUTE.
> > if (name[0] != starting_directory[0]) {
> > /* Cannot convert a path on a different drive letter to relative */
> > return NULL;
??? Why not? simply return the original name without any changes, it's
better than failing.
> > if (strlen(tname) != 1 && tname[0] != '/') {
> > strcat(tname, "/");
> > }
This again works only on Unix.
> > /* Skip common characters in both paths */
> > while (*srcname == *srcdir && *srcname != '\0' && *srcdir != '\0') {
> > ++srcname;
> > ++srcdir;
> > }
> > /* Now rewind to last common / */
> > while (*srcname != '/' && *srcdir != '/' && srcdir != starting_directory) {
> > --srcname;
> > --srcdir;
> > }
What will happen here if the argument of relpath is exactly identical
to starting_directory?
Also, the test `srcdir != starting_directory' will not DTRT on
Windows, because the first character is not a slash.
> > /* If the resulting path is empty, return a '.' */
> > if (dest == apath) {
> > *dest++ = '.';
> > }
Not TRT on Windows.
Thanks again for working on this.