never actually been invoked. GHC has an option for generating
instrumented code that records code coverage as part of the
<ulink url="http://www.haskell.org/hpc">Haskell Program Coverage
- </ulink>(HPC) toolkit. HPC tools can be used to render the
- outputed code coverage infomation into human understandable
- format.
- </para>
+ </ulink>(HPC) toolkit, which is included with GHC. HPC tools can
+ be used to render the generated code coverage information into
+ human understandable format. </para>
<para>
- HPC provides coverage information of two kinds: source coverage
- and boolean-control coverage. Source coverage is the extent to
- which every part of the program was used, measured at three
- different levels: declarations (both top-level and local),
- alternatives (among several equations or case branches) and
- expressions (at every level). Boolean coverage is the extent to
- which each of the values True and False is obtained in every
- syntactic boolean context (ie. guard, condition, qualifier).
- </para>
+ Correctly instrumented code provides coverage information of two
+ kinds: source coverage and boolean-control coverage. Source
+ coverage is the extent to which every part of the program was
+ used, measured at three different levels: declarations (both
+ top-level and local), alternatives (among several equations or
+ case branches) and expressions (at every level). Boolean
+ coverage is the extent to which each of the values True and
+ False is obtained in every syntactic boolean context (ie. guard,
+ condition, qualifier). </para>
<para>
- HPC displays both kinds of information in two different ways:
- textual reports with summary statistics (hpc-report) and sources
- with color mark-up (hpc-markup). For boolean coverage, there
+ HPC displays both kinds of information in two primary ways:
+ textual reports with summary statistics (hpc report) and sources
+ with color mark-up (hpc markup). For boolean coverage, there
are four possible outcomes for each guard, condition or
qualifier: both True and False values occur; only True; only
False; never evaluated. In hpc-markup output, highlighting with
<sect2><title>A small example: Reciprocation</title>
<para>
- For an example we have a program which computes exact decimal
+ For an example we have a program, called Recip.hs, which computes exact decimal
representations of reciprocals, with recurring parts indicated in
- brackets. We first build an instrumented version using the
- hpc-build script. Assuming the source file is Recip.hs.
+ brackets.
</para>
<programlisting>
reciprocal :: Int -> (String, Int)
main
</programlisting>
-` <para>The HPC intrumentation is enabled using the -fhpc flag.
+ <para>The HPC instrumentation is enabled using the -fhpc flag.
</para>
<screen>
$ ghc -fhpc Recip.hs --make
</screen>
<para>HPC index (.mix) files are placed placed in .hpc subdirectory. These can be considered like
- the .hi files for HPC. They contain information about what parts of the haskell each modules.
+ the .hi files for HPC.
</para>
<screen>
$ ./Recip
1/3
= 0.(3)
</screen>
- <para>Now for a textual summary of coverage:</para>
+ <para>We can generate a textual summary of coverage:</para>
<screen>
-$ hpc-report Recip
+$ hpc report Recip
80% expressions used (81/101)
12% boolean coverage (1/8)
14% guards (1/7), 3 always True,
100% local declarations used (9/9)
100% top-level declarations used (5/5)
</screen>
- <para>Finally, we generate a marked-up version of the source.</para>
+ <para>We can also generate a marked-up version of the source.</para>
<screen>
-$ hpc-markup Recip
+$ hpc markup Recip
writing Recip.hs.html
</screen>
-<figure>
- <title>Recip.hs.html</title>
- <graphic fileref="images/Recip.png"></graphic>
- </figure>
+ <para>
+ This generates one file per Haskell module, and 4 index files,
+ hpc_index.html, hpc_index_alt.html, hpc_index_exp.html,
+ hpc_index_fun.html.
+ </para>
+ </sect2>
+
+ <sect2><title>Options for instrumenting code for coverage</title>
+ <para>
+ Turning on code coverage is easy, use the -fhpc flag.
+ Instrumented and non-instrumented can be freely mixed.
+ When compiling the Main module GHC automatically detects when there
+ is an hpc compiled file, and adds the correct initialization code.
+ </para>
+
+ </sect2>
+
+ <sect2><title>The hpc toolkit</title>
+
+ <para>
+ The hpc toolkit uses a cvs/svn/darcs-like interface, where a
+ single binary contains many function units.</para>
+<screen>
+$ hpc
+Usage: hpc COMMAND ...
+
+Commands:
+ help Display help for hpc or a single command
+Reporting Coverage:
+ report Output textual report about program coverage
+ markup Markup Haskell source with program coverage
+Processing Coverage files:
+ combine Combine multiple .tix files in a single .tix files
+Coverage Overlays:
+ overlay Generate a .tix file from an overlay file
+ draft Generate draft overlay that provides 100% coverage
+Others:
+ show Show .tix file in readable, verbose format
+ version Display version for hpc
+</screen>
+
+ <para>In general, these options act on .tix file after an
+ instrumented binary has generated it, which hpc acting as a
+ conduit between the raw .tix file, and the more detailed reports
+ produced.
+ </para>
+
+ <para>
+ The hpc tool assumes you are in the top-level directory of
+ the location where you built your application, and the .tix
+ file is in the same top-level directory. You can use the
+ flag --srcdir to use hpc for any other directory, and use
+ --srcdir multiple times to analyse programs compiled from
+ difference locations, as is typical for packages.
+ </para>
+
+ <para>
+ We now explain in more details the major modes of hpc.
+ </para>
+
+ <sect3><title>hpc report</title>
+ <para>hpc report gives a textual report of coverage. By default,
+ all modules and packages are considered in generating report,
+ unless include or exclude are used. The report is a summary
+ unless the --per-module flag is used. The --xml-output option
+ allows for tools to use hpc to glean coverage.
+ </para>
+<screen>
+$ hpc help report
+Usage: hpc report [OPTION] .. <TIX_FILE> [<MODULE> [<MODULE> ..]]
+
+Options:
+
+ --per-module show module level detail
+ --decl-list show unused decls
+ --exclude=[PACKAGE:][MODULE] exclude MODULE and/or PACKAGE
+ --include=[PACKAGE:][MODULE] include MODULE and/or PACKAGE
+ --srcdir=DIR path to source directory of .hs files
+ multi-use of srcdir possible
+ --hpcdir=DIR sub-directory that contains .mix files
+ default .hpc [rarely used]
+ --xml-output show output in XML
+</screen>
+ </sect3>
+ <sect3><title>hpc markup</title>
+ <para>hpc markup marks up source files into colored html.
+ </para>
+<screen>
+% hpc help markup
+Usage: hpc markup [OPTION] .. <TIX_FILE> [<MODULE> [<MODULE> ..]]
+
+Options:
+
+ --exclude=[PACKAGE:][MODULE] exclude MODULE and/or PACKAGE
+ --include=[PACKAGE:][MODULE] include MODULE and/or PACKAGE
+ --srcdir=DIR path to source directory of .hs files
+ multi-use of srcdir possible
+ --hpcdir=DIR sub-directory that contains .mix files
+ default .hpc [rarely used]
+ --fun-entry-count show top-level function entry counts
+ --highlight-covered highlight covered code, rather that code gaps
+ --destdir=DIR path to write output to
+</screen>
+
+ </sect3>
+ <sect3><title>hpc combine</title>
+ <para>hpc combine is the swiss army knife of hpc. Typically, combine is used
+ to add .tix files together to get the combined total coverage. However, it can
+ also be used to take the difference between .tix files, to subtract one
+ .tix file from another, and to zero the .tix files. hpc combine does not
+ change the original .tix file; it generates a new .tix file.
+ </para>
+<screen>
+hpc help combine
+Usage: hpc combine [OPTION] .. <TIX_FILE> [<TIX_FILE> [<TIX_FILE> ..]]
- </sect2>
+Options:
+
+ --exclude=[PACKAGE:][MODULE] exclude MODULE and/or PACKAGE
+ --include=[PACKAGE:][MODULE] include MODULE and/or PACKAGE
+ --output=FILE output FILE
+ --combine=FUNCTION combine .tix files with join function, default = ADD
+ FUNCTION = ADD | DIFF | SUB | ZERO
+ --post-invert invert output; ticked becomes unticked, unticked becomes ticked
+</screen>
+ </sect3>
+ <sect3><title>hpc overlay and hpc draft</title>
+ <para>
+ Overlays are an experimental feature of HPC, a textual description
+ of coverage. hpc draft is used to generate a draft overlay from a .tix file,
+ and hpc overlay generates a .tix files from an overlay.
+ </para>
+<screen>
+% hpc help overlay
+Usage: hpc overlay [OPTION] .. <OVERLAY_FILE> [<OVERLAY_FILE> [...]]
+
+Options:
+
+ --srcdir=DIR path to source directory of .hs files
+ multi-use of srcdir possible
+ --hpcdir=DIR sub-directory that contains .mix files
+ default .hpc [rarely used]
+ --output=FILE output FILE
+% hpc help draft
+Usage: hpc draft [OPTION] .. <TIX_FILE>
+
+Options:
+
+ --exclude=[PACKAGE:][MODULE] exclude MODULE and/or PACKAGE
+ --include=[PACKAGE:][MODULE] include MODULE and/or PACKAGE
+ --srcdir=DIR path to source directory of .hs files
+ multi-use of srcdir possible
+ --hpcdir=DIR sub-directory that contains .mix files
+ default .hpc [rarely used]
+ --output=FILE output FILE
+</screen>
+ </sect3>
+ </sect2>
+ <sect2><title>Caveats and Shortcomings of Haskell Program Coverage</title>
+ <para>
+ HPC does not attempt to lock the .tix file, so multiple concurrently running
+ binaries in the same directory will exhibit a race condition. There is no way
+ to change the name of the .tix file generated, apart from renaming the binary.
+ HPC does not work with GHCi.
+ </para>
+ </sect2>
</sect1>
<sect1 id="ticky-ticky">
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