Merge lp:~barry/click/docs-n-stuff into lp:click

[Barry Warsaw]

A bunch of small changes, some good, some questionable. ;)

* Convert the docs to reStructuredText and sphinx-ify them. `make html` in the doc/ directory to build.
* clickpreload_init(): as per dlsym() manpage, clear the dlerror() before checking. Probably not strictly necessary, but can't hurt.
* test_build() assumes umask 022 in the environment. The test and/or system should perhaps be made more robust, but since my env typically uses umask 002, add a decorator for the test to temporary smash the umask. At least this gets the test passing for me.
* Obviously, ignore the doc/ directory for PEP 8 checks
* Added a question in file-format.rst

[lp:~barry/click/docs-n-stuff]

32. By Barry Warsaw on 2013-04-15

typo

33. By Barry Warsaw on 2013-04-16

Changes based on feedback from Colin.

* Fix the copyright for the documentation.
* Remove question which I now understand ;)
* Fix reST markup.
* Restore an idiom common on the eastern side of the Atlantic
* Strictly speaking, the only check for dlsym() failing is to check dlerror(),
  since dlsym() returning NULL could be valid.

=== modified file '.bzrignore'
--- .bzrignore	2013-04-10 15:55:06 +0000
+++ .bzrignore	2013-04-16 17:28:26 +0000
@@ -1,2 +1,6 @@
 __pycache__
 ./click_installer.egg-info
+_build/doctrees
+_build/html
+doc/_build/doctrees
+doc/_build/html

=== modified file 'clickpackage/tests/test_build.py'
--- clickpackage/tests/test_build.py	2013-04-12 13:26:40 +0000
+++ clickpackage/tests/test_build.py	2013-04-16 17:28:26 +0000
@@ -30,6 +30,21 @@
 from clickpackage.tests.helpers import TestCase, mkfile, touch
 
 
+# BAW 2013-04-15: Some tests require umask 022.  Use this decorator to
+# temporarily tweak the process's umask.  The test -- or system -- should
+# probably be made more robust instead.
+def umask(force_umask):
+    def decorator(func):
+        def wrapper(*args, **kws):
+            old_umask = os.umask(force_umask)
+            try:
+                return func(*args, **kws)
+            finally:
+                os.umask(old_umask)
+        return wrapper
+    return decorator
+
+
 class TestClickBuilder(TestCase):
     def test_read_metadata(self):
         self.use_temp_dir()
@@ -64,6 +79,7 @@
         return subprocess.check_output(
             ["dpkg-deb", "-I", path, name], universal_newlines=True)
 
+    @umask(0o22)
     def test_build(self):
         self.use_temp_dir()
         scratch = os.path.join(self.temp_dir, "scratch")

=== modified file 'clickpackage/tests/test_static.py'
--- clickpackage/tests/test_static.py	2013-04-10 15:55:06 +0000
+++ clickpackage/tests/test_static.py	2013-04-16 17:28:26 +0000
@@ -32,7 +32,7 @@
     def all_paths(self):
         paths = []
         for dirpath, dirnames, filenames in os.walk("."):
-            for ignore in ".bzr", "__pycache__":
+            for ignore in ('doc', ".bzr", "__pycache__"):
                 if ignore in dirnames:
                     dirnames.remove(ignore)
             filenames = [

=== added file 'doc/Makefile'
--- doc/Makefile	1970-01-01 00:00:00 +0000
+++ doc/Makefile	2013-04-16 17:28:26 +0000
@@ -0,0 +1,153 @@
+# Makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+PAPER         =
+BUILDDIR      = _build
+
+# Internal variables.
+PAPEROPT_a4     = -D latex_paper_size=a4
+PAPEROPT_letter = -D latex_paper_size=letter
+ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
+# the i18n builder cannot share the environment and doctrees with the others
+I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
+
+.PHONY: help clean html dirhtml singlehtml pickle json htmlhelp qthelp devhelp epub latex latexpdf text man changes linkcheck doctest gettext
+
+help:
+	@echo "Please use \`make <target>' where <target> is one of"
+	@echo "  html       to make standalone HTML files"
+	@echo "  dirhtml    to make HTML files named index.html in directories"
+	@echo "  singlehtml to make a single large HTML file"
+	@echo "  pickle     to make pickle files"
+	@echo "  json       to make JSON files"
+	@echo "  htmlhelp   to make HTML files and a HTML help project"
+	@echo "  qthelp     to make HTML files and a qthelp project"
+	@echo "  devhelp    to make HTML files and a Devhelp project"
+	@echo "  epub       to make an epub"
+	@echo "  latex      to make LaTeX files, you can set PAPER=a4 or PAPER=letter"
+	@echo "  latexpdf   to make LaTeX files and run them through pdflatex"
+	@echo "  text       to make text files"
+	@echo "  man        to make manual pages"
+	@echo "  texinfo    to make Texinfo files"
+	@echo "  info       to make Texinfo files and run them through makeinfo"
+	@echo "  gettext    to make PO message catalogs"
+	@echo "  changes    to make an overview of all changed/added/deprecated items"
+	@echo "  linkcheck  to check all external links for integrity"
+	@echo "  doctest    to run all doctests embedded in the documentation (if enabled)"
+
+clean:
+	-rm -rf $(BUILDDIR)/*
+
+html:
+	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html
+	@echo
+	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
+
+dirhtml:
+	$(SPHINXBUILD) -b dirhtml $(ALLSPHINXOPTS) $(BUILDDIR)/dirhtml
+	@echo
+	@echo "Build finished. The HTML pages are in $(BUILDDIR)/dirhtml."
+
+singlehtml:
+	$(SPHINXBUILD) -b singlehtml $(ALLSPHINXOPTS) $(BUILDDIR)/singlehtml
+	@echo
+	@echo "Build finished. The HTML page is in $(BUILDDIR)/singlehtml."
+
+pickle:
+	$(SPHINXBUILD) -b pickle $(ALLSPHINXOPTS) $(BUILDDIR)/pickle
+	@echo
+	@echo "Build finished; now you can process the pickle files."
+
+json:
+	$(SPHINXBUILD) -b json $(ALLSPHINXOPTS) $(BUILDDIR)/json
+	@echo
+	@echo "Build finished; now you can process the JSON files."
+
+htmlhelp:
+	$(SPHINXBUILD) -b htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
+	@echo
+	@echo "Build finished; now you can run HTML Help Workshop with the" \
+	      ".hhp project file in $(BUILDDIR)/htmlhelp."
+
+qthelp:
+	$(SPHINXBUILD) -b qthelp $(ALLSPHINXOPTS) $(BUILDDIR)/qthelp
+	@echo
+	@echo "Build finished; now you can run "qcollectiongenerator" with the" \
+	      ".qhcp project file in $(BUILDDIR)/qthelp, like this:"
+	@echo "# qcollectiongenerator $(BUILDDIR)/qthelp/ClickPackages.qhcp"
+	@echo "To view the help file:"
+	@echo "# assistant -collectionFile $(BUILDDIR)/qthelp/ClickPackages.qhc"
+
+devhelp:
+	$(SPHINXBUILD) -b devhelp $(ALLSPHINXOPTS) $(BUILDDIR)/devhelp
+	@echo
+	@echo "Build finished."
+	@echo "To view the help file:"
+	@echo "# mkdir -p $$HOME/.local/share/devhelp/ClickPackages"
+	@echo "# ln -s $(BUILDDIR)/devhelp $$HOME/.local/share/devhelp/ClickPackages"
+	@echo "# devhelp"
+
+epub:
+	$(SPHINXBUILD) -b epub $(ALLSPHINXOPTS) $(BUILDDIR)/epub
+	@echo
+	@echo "Build finished. The epub file is in $(BUILDDIR)/epub."
+
+latex:
+	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
+	@echo
+	@echo "Build finished; the LaTeX files are in $(BUILDDIR)/latex."
+	@echo "Run \`make' in that directory to run these through (pdf)latex" \
+	      "(use \`make latexpdf' here to do that automatically)."
+
+latexpdf:
+	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
+	@echo "Running LaTeX files through pdflatex..."
+	$(MAKE) -C $(BUILDDIR)/latex all-pdf
+	@echo "pdflatex finished; the PDF files are in $(BUILDDIR)/latex."
+
+text:
+	$(SPHINXBUILD) -b text $(ALLSPHINXOPTS) $(BUILDDIR)/text
+	@echo
+	@echo "Build finished. The text files are in $(BUILDDIR)/text."
+
+man:
+	$(SPHINXBUILD) -b man $(ALLSPHINXOPTS) $(BUILDDIR)/man
+	@echo
+	@echo "Build finished. The manual pages are in $(BUILDDIR)/man."
+
+texinfo:
+	$(SPHINXBUILD) -b texinfo $(ALLSPHINXOPTS) $(BUILDDIR)/texinfo
+	@echo
+	@echo "Build finished. The Texinfo files are in $(BUILDDIR)/texinfo."
+	@echo "Run \`make' in that directory to run these through makeinfo" \
+	      "(use \`make info' here to do that automatically)."
+
+info:
+	$(SPHINXBUILD) -b texinfo $(ALLSPHINXOPTS) $(BUILDDIR)/texinfo
+	@echo "Running Texinfo files through makeinfo..."
+	make -C $(BUILDDIR)/texinfo info
+	@echo "makeinfo finished; the Info files are in $(BUILDDIR)/texinfo."
+
+gettext:
+	$(SPHINXBUILD) -b gettext $(I18NSPHINXOPTS) $(BUILDDIR)/locale
+	@echo
+	@echo "Build finished. The message catalogs are in $(BUILDDIR)/locale."
+
+changes:
+	$(SPHINXBUILD) -b changes $(ALLSPHINXOPTS) $(BUILDDIR)/changes
+	@echo
+	@echo "The overview file is in $(BUILDDIR)/changes."
+
+linkcheck:
+	$(SPHINXBUILD) -b linkcheck $(ALLSPHINXOPTS) $(BUILDDIR)/linkcheck
+	@echo
+	@echo "Link check complete; look for any errors in the above output " \
+	      "or in $(BUILDDIR)/linkcheck/output.txt."
+
+doctest:
+	$(SPHINXBUILD) -b doctest $(ALLSPHINXOPTS) $(BUILDDIR)/doctest
+	@echo "Testing of doctests in the sources finished, look at the " \
+	      "results in $(BUILDDIR)/doctest/output.txt."

=== added directory 'doc/_build'
=== added directory 'doc/_static'
=== added directory 'doc/_templates'
=== added file 'doc/conf.py'
--- doc/conf.py	1970-01-01 00:00:00 +0000
+++ doc/conf.py	2013-04-16 17:28:26 +0000
@@ -0,0 +1,242 @@
+# -*- coding: utf-8 -*-
+#
+# Click Packages documentation build configuration file, created by
+# sphinx-quickstart on Mon Apr 15 11:34:57 2013.
+#
+# This file is execfile()d with the current directory set to its containing dir.
+#
+# Note that not all possible configuration values are present in this
+# autogenerated file.
+#
+# All configuration values have a default; values that are commented out
+# serve to show the default.
+
+import sys, os
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+#sys.path.insert(0, os.path.abspath('.'))
+
+# -- General configuration -----------------------------------------------------
+
+# If your documentation needs a minimal Sphinx version, state it here.
+#needs_sphinx = '1.0'
+
+# Add any Sphinx extension module names here, as strings. They can be extensions
+# coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
+extensions = []
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = ['_templates']
+
+# The suffix of source filenames.
+source_suffix = '.rst'
+
+# The encoding of source files.
+#source_encoding = 'utf-8-sig'
+
+# The master toctree document.
+master_doc = 'index'
+
+# General information about the project.
+project = u'Click Packages'
+copyright = u'2013, Canonical Ltd.'
+
+# The version info for the project you're documenting, acts as replacement for
+# |version| and |release|, also used in various other places throughout the
+# built documents.
+#
+# The short X.Y version.
+version = '0.1'
+# The full version, including alpha/beta/rc tags.
+release = '0.1'
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#language = None
+
+# There are two options for replacing |today|: either, you set today to some
+# non-false value, then it is used:
+#today = ''
+# Else, today_fmt is used as the format for a strftime call.
+#today_fmt = '%B %d, %Y'
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+exclude_patterns = ['_build']
+
+# The reST default role (used for this markup: `text`) to use for all documents.
+#default_role = None
+
+# If true, '()' will be appended to :func: etc. cross-reference text.
+#add_function_parentheses = True
+
+# If true, the current module name will be prepended to all description
+# unit titles (such as .. function::).
+#add_module_names = True
+
+# If true, sectionauthor and moduleauthor directives will be shown in the
+# output. They are ignored by default.
+#show_authors = False
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = 'sphinx'
+
+# A list of ignored prefixes for module index sorting.
+#modindex_common_prefix = []
+
+
+# -- Options for HTML output ---------------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+html_theme = 'default'
+
+# Theme options are theme-specific and customize the look and feel of a theme
+# further.  For a list of options available for each theme, see the
+# documentation.
+#html_theme_options = {}
+
+# Add any paths that contain custom themes here, relative to this directory.
+#html_theme_path = []
+
+# The name for this set of Sphinx documents.  If None, it defaults to
+# "<project> v<release> documentation".
+#html_title = None
+
+# A shorter title for the navigation bar.  Default is the same as html_title.
+#html_short_title = None
+
+# The name of an image file (relative to this directory) to place at the top
+# of the sidebar.
+#html_logo = None
+
+# The name of an image file (within the static path) to use as favicon of the
+# docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
+# pixels large.
+#html_favicon = None
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = ['_static']
+
+# If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
+# using the given strftime format.
+#html_last_updated_fmt = '%b %d, %Y'
+
+# If true, SmartyPants will be used to convert quotes and dashes to
+# typographically correct entities.
+#html_use_smartypants = True
+
+# Custom sidebar templates, maps document names to template names.
+#html_sidebars = {}
+
+# Additional templates that should be rendered to pages, maps page names to
+# template names.
+#html_additional_pages = {}
+
+# If false, no module index is generated.
+#html_domain_indices = True
+
+# If false, no index is generated.
+#html_use_index = True
+
+# If true, the index is split into individual pages for each letter.
+#html_split_index = False
+
+# If true, links to the reST sources are added to the pages.
+#html_show_sourcelink = True
+
+# If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
+#html_show_sphinx = True
+
+# If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
+#html_show_copyright = True
+
+# If true, an OpenSearch description file will be output, and all pages will
+# contain a <link> tag referring to it.  The value of this option must be the
+# base URL from which the finished HTML is served.
+#html_use_opensearch = ''
+
+# This is the file name suffix for HTML files (e.g. ".xhtml").
+#html_file_suffix = None
+
+# Output file base name for HTML help builder.
+htmlhelp_basename = 'ClickPackagesdoc'
+
+
+# -- Options for LaTeX output --------------------------------------------------
+
+latex_elements = {
+# The paper size ('letterpaper' or 'a4paper').
+#'papersize': 'letterpaper',
+
+# The font size ('10pt', '11pt' or '12pt').
+#'pointsize': '10pt',
+
+# Additional stuff for the LaTeX preamble.
+#'preamble': '',
+}
+
+# Grouping the document tree into LaTeX files. List of tuples
+# (source start file, target name, title, author, documentclass [howto/manual]).
+latex_documents = [
+  ('index', 'ClickPackages.tex', u'Click Packages Documentation',
+   u'Colin Watson', 'manual'),
+]
+
+# The name of an image file (relative to this directory) to place at the top of
+# the title page.
+#latex_logo = None
+
+# For "manual" documents, if this is true, then toplevel headings are parts,
+# not chapters.
+#latex_use_parts = False
+
+# If true, show page references after internal links.
+#latex_show_pagerefs = False
+
+# If true, show URL addresses after external links.
+#latex_show_urls = False
+
+# Documents to append as an appendix to all manuals.
+#latex_appendices = []
+
+# If false, no module index is generated.
+#latex_domain_indices = True
+
+
+# -- Options for manual page output --------------------------------------------
+
+# One entry per manual page. List of tuples
+# (source start file, name, description, authors, manual section).
+man_pages = [
+    ('index', 'clickpackages', u'Click Packages Documentation',
+     [u'Colin Watson'], 1)
+]
+
+# If true, show URL addresses after external links.
+#man_show_urls = False
+
+
+# -- Options for Texinfo output ------------------------------------------------
+
+# Grouping the document tree into Texinfo files. List of tuples
+# (source start file, target name, title, author,
+#  dir menu entry, description, category)
+texinfo_documents = [
+  ('index', 'ClickPackages', u'Click Packages Documentation',
+   u'Colin Watson', 'ClickPackages', 'One line description of project.',
+   'Miscellaneous'),
+]
+
+# Documents to append as an appendix to all manuals.
+#texinfo_appendices = []
+
+# If false, no module index is generated.
+#texinfo_domain_indices = True
+
+# How to display URL addresses: 'footnote', 'no', or 'inline'.
+#texinfo_show_urls = 'footnote'

=== renamed file 'doc/constraints' => 'doc/constraints.rst'
--- doc/constraints	2013-04-12 10:13:31 +0000
+++ doc/constraints.rst	2013-04-16 17:28:26 +0000
@@ -1,28 +1,30 @@
+==================
 Design constraints
-------------------
+==================
 
 Building packages
 =================
 
  * Building packages should not require any more than the Python standard
-   library.  In particular, it should not require dpkg, python-debian, or
-   any other such Debian-specific tools.
-
-   Rationale: We want people to be able to build Click packages easily on
-   any platform (or at least any platform that can manage a Python
-   installation, which is not too onerous a requirement).
+   library.  In particular, it should not require dpkg, python-debian, or any
+   other such Debian-specific tools.
+
+   Rationale: We want people to be able to build Click packages easily on any
+   platform (or at least any platform that can manage a Python installation,
+   which is not too onerous a requirement).
+
 
 Installing packages
 ===================
 
  * For the purpose of rapid prototyping, package installation is also
    implemented in Python.  This may of course use Debian/Ubuntu-specific
-   tools, since it will always be running on an Ubuntu system.  In future,
-   it will probably be reimplemented in C for performance.
+   tools, since it will always be running on an Ubuntu system.  In future, it
+   will probably be re-implemented in C for performance.
 
  * Reading the system dpkg database is forbidden.  This is partly to ensure
-   strict separation, and partly because the system dpkg database is large
-   and therefore slow to read.
+   strict separation, and partly because the system dpkg database is large and
+   therefore slow to read.
 
  * Nothing should require root, although it may be acceptable to make use of
    root-only facilities if available (but remembering to pay attention to

=== renamed file 'doc/file-format' => 'doc/file-format.rst'
--- doc/file-format	2013-04-12 12:46:45 +0000
+++ doc/file-format.rst	2013-04-16 17:28:26 +0000
@@ -1,5 +1,6 @@
+========================================
 "Click" package file format, version 0.1
-----------------------------------------
+========================================
 
 This specification covers a packaging format intended for use by
 self-contained third-party applications.  It is intentionally designed to be
@@ -64,6 +65,7 @@
 to refuse to install it.  The package manager must enforce the permitted
 text of this script.
 
+
 Data area
 =========
 

=== renamed file 'doc/hooks' => 'doc/hooks.rst'
--- doc/hooks	2013-04-11 16:57:36 +0000
+++ doc/hooks.rst	2013-04-16 17:28:26 +0000
@@ -1,5 +1,6 @@
+=====
 Hooks
------
+=====
 
 Of course, any sensible packaging format needs a hook mechanism of some
 kind; just unpacking a filesystem tarball isn't going to cut it.  But part
@@ -53,7 +54,7 @@
 What we can do with reasonable safety is populate symlink farms.  As a
 strawman proposal, consider the following:
 
- * An integrated-with system package may add *.hook files to
+ * An integrated-with system package may add ``*.hook`` files to
    /usr/share/click-package/hooks/.  These are standard Debian-style control
    files with the following keys:
 
@@ -69,7 +70,7 @@
    one %s substitution: the package manager substitutes an identifier
    provided by the Click package into it and creates the resulting path as a
    symlink to a path provided by the Click package.
-   
+
    If the Exec key is present, its value is executed as if passed to the
    shell after the above symlink is created.
 
@@ -77,11 +78,11 @@
 
  * A Click package may include a "hooks" entry in its metadata (exact format
    TBD).  If present, it must contain a mapping of keys to values.  The keys
-   are used to look up *.hook files with an equal Hook field (see above).
+   are used to look up ``*.hook`` files with an equal Hook field (see above).
    The values are symlink target paths used by the package manager when
-   creating symlinks according to the Pattern field in *.hook files.
+   creating symlinks according to the Pattern field in ``*.hook`` files.
 
- * There should be a dh_clickpackage which installs the *.hook files in
+ * There should be a dh_clickpackage which installs the ``*.hook`` files in
    system packages and adds maintainer script fragments to cause
    click-package to catch up with any newly-provided hooks.
 
@@ -89,13 +90,13 @@
    Click package to avoid code duplication between system and Click package
    handling, although we must do so asynchronously and any errors must not
    block the installation of Click packages.  If "Trigger: yes" is set in a
-   *.hook file, then click-install will activate an asynchronous D-Bus
+   ``*.hook`` file, then click-install will activate an asynchronous D-Bus
    service at the end of installation, passing the names of all the changed
    paths resulting from Pattern key expansions; this will activate any file
    triggers matching those paths, and process all the packages that enter
    the triggers-pending state as a result.
 
-Thus, a worked example would have:
+Thus, a worked example would have::
 
   /usr/share/click-package/hooks/unity-lens-help.hook
     Hook: unity-lens-help

=== added file 'doc/index.rst'
--- doc/index.rst	1970-01-01 00:00:00 +0000
+++ doc/index.rst	2013-04-16 17:28:26 +0000
@@ -0,0 +1,35 @@
+.. Click Packages documentation master file, created by
+   sphinx-quickstart on Mon Apr 15 11:34:57 2013.
+   You can adapt this file completely to your liking, but it should at least
+   contain the root `toctree` directive.
+
+==============
+Click packages
+==============
+
+*Click* is the code name used to describe a packaging format for Ubuntu mobile
+applications.  This format specifies how individual apps are delivered to
+mobile devices, how they are packed into distributable format, and how they
+are installed on a mobile device by a system provided package manager.  At a
+minimum they assume that a base system exists providing all the necessary
+infrastructure and dependencies needed in order to install and run such apps.
+
+The click packaging format is completely independent from facilities to do
+full-system installations or upgrades.
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   file-format.rst
+   constraints.rst
+   hooks.rst
+
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`

=== modified file 'preload/clickpreload.c'
--- preload/clickpreload.c	2013-04-12 09:59:54 +0000
+++ preload/clickpreload.c	2013-04-16 17:28:26 +0000
@@ -42,12 +42,15 @@
 #define GET_NEXT_SYMBOL(name) \
     do { \
         libc_##name = dlsym (RTLD_NEXT, #name); \
-        if (!libc_##name || dlerror ()) \
+        if (dlerror ()) \
             _exit (1); \
     } while (0)
 
 void __attribute__ ((constructor)) clickpreload_init (void)
 {
+    /* Clear any old error conditions, albeit unlikely, as per dlsym(2) */
+    dlerror ();
+
     GET_NEXT_SYMBOL (chown);
     GET_NEXT_SYMBOL (execvp);
     GET_NEXT_SYMBOL (fchown);