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This queue is for tickets about the Devel-Cover CPAN distribution.

Report information
The Basics
Id: 45054
Status: stalled
Priority: 0/
Queue: Devel-Cover

People
Owner: PJCJ [...] cpan.org
Requestors: td091116 [...] th-dorner.de
Cc:
AdminCc:

Bug Information
Severity: Normal
Broken in:
  • 0.59
  • 0.64
Fixed in: (no value)



Subject: gcov2perl suspectible to different usage of same C/C++ include file (esp. templates)
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After applying the patches of my reports 44864 and 45028 I noticed a third problem where gcov2perl in combination with cover leads to incorrect results. The problem again occurs for the instances of include files. gcov is called with option -l (--long-file-names) in order to get coverage data for all statements inside of include files (e.g. inline methods/functions). The coverage database is build on the assumption that each gcov run for identical (include) files marks the same lines as executable code lines. Unfortunately this assumption is not always true. Especially sensitive are C++ templates. Consider the following example, a default constructor for a C++ template: template<size_t LENGTH> inline TFixString<LENGTH>::TFixString() { TFixStringBase::copystring(m_Str, LENGTH, "", 0); } Depending on whether the default constructor is actually used in a C++ source (.cc or .cpp) it will be instantiated (created) or not. So the possible corresponding gcov results can be like the following: 1. (constructor is used): -: 66:TFixString<LENGTH>::TFixString() 216: 67:{ 216: 68: TFixStringBase::copystring(m_Str, LENGTH, "", 0); -: 69:} 2. (constructor can be used, but isn't): -: 66:TFixString<LENGTH>::TFixString() #####: 67:{ #####: 68: TFixStringBase::copystring(m_Str, LENGTH, "", 0); -: 69:} 3. (constructor can not be used): -: 66:TFixString<LENGTH>::TFixString() -: 67:{ -: 68: TFixStringBase::copystring(m_Str, LENGTH, "", 0); -: 69:} Coverage data for includes where case 3 and at least one of the other two cases occur will be counted incorrect as gcov2perl doesn't match coverage count with line numbers directly. The cover.12 file contains a simple list of coverage counts for each line of a source that has been considered executable (not matching '^ *-:') in that instance while the list of the actual line numbers are stored in one file per source (== only once and not for each incarnation) in the structure directory. While this is good as it possible saves a lot of disk space this results in bad data for something like above example. I guess fixing this would be a major effort as it needs redesigning the database of Devel::Cover but please keep this problem in mind whenever you are going to change that DB design anyway.
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Sounds like this might need similar treatment to what we do when perl creates different code in different runs of the same file. Unfortunately that is horrible and probably the cause of the most bugs in the module, so I'm loathe to attack that at the moment, but I'll leave the ticket here as a reminder. Thanks,


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