Build systems specify how sources are transformed into deliverables, and hence must be carefully maintained to ensure that deliverables are assembled correctly. Similar to source code, build systems tend to grow in complexity unless specifications are refactored. This paper describes how clone detection can aid in quality assessments that determine if and where build refactoring effort should be applied. We gauge cloning rates in build systems by collecting and analyzing a benchmark comprising 3,872 build systems. Analysis of the benchmark reveals that: (1) build systems tend to have higher cloning rates than other software artifacts, (2) recent build technologies tend to be more prone to cloning, especially of configuration details like API dependencies, than older technologies, and (3) build systems that have fewer clones achieve higher levels of reuse via mechanisms not offered by build technologies. Our findings aided in refactoring a large industrial build system containing 1.1 million lines.

1. Collecting and Leveraging a
Benchmark of Build System Clones
to Aid in Quality Assessments
Shane
McIntosh
@shane_mcintosh
shanemcintosh@acm.org

2. Collecting and Leveraging a
Benchmark of Build System Clones
to Aid in Quality Assessments
Shane
McIntosh
@shane_mcintosh
shanemcintosh@acm.org
Martin
Poehlmann
Elmar
Juergens

3. Collecting and Leveraging a
Benchmark of Build System Clones
to Aid in Quality Assessments
Shane
McIntosh
@shane_mcintosh
shanemcintosh@acm.org
Martin
Poehlmann
Elmar
Juergens
Audris
Mockus

4. Collecting and Leveraging a
Benchmark of Build System Clones
to Aid in Quality Assessments
Shane
McIntosh
@shane_mcintosh
shanemcintosh@acm.org
Bram
Adams
Ahmed E.
Hassan
Martin
Poehlmann
Elmar
Juergens
Audris
Mockus

5. Collecting and Leveraging a
Benchmark of Build System Clones
to Aid in Quality Assessments
Shane
McIntosh
@shane_mcintosh
shanemcintosh@acm.org
Bram
Adams
Ahmed E.
Hassan
Martin
Poehlmann
Elmar
Juergens
Audris
Mockus
Brigitte
Haupt
Christian
Wagner

6. What is a build system?
Source
code

7. What is a build system?
Source
code
Deliverable

8. .tex
.c
.cc
.o
.o
.dvi
.a
.exe
.pdf
.deb
Build systems describe how sources are
translated into deliverables
3

9. 4
Step 1 -
Configuration
Step 2 -
Construction
Step 3 -
Certification
Step 4 -
Packaging
Step 5 -
Deployment

10. 5
Step 1 - Configuration

11. 6
Step 2 - Construction

12. 7
Step 3 - Certification

13. 8
Step 4 - Packaging

14. 9
Step 5 - Deployment

15. Continuous Integration:!
Enabled by the
build system
10

16. Continuous Integration:!
Enabled by the
build system
10
Commit
Commit
9719cf0

17. Continuous Integration:!
Enabled by the
build system
10
Commit
Build
Commit
9719cf0

18. Continuous Integration:!
Enabled by the
build system
10
Commit
Build
Test
Commit
9719cf0

19. Continuous Integration:!
Enabled by the
build system
10
Commit
Build
Test
Report
Commit
9719cf0
broke the
build!
Commit
9719cf0

20. Continuous Integration:!
Enabled by the
build system
10
Commit
Build
Test
Report
Commit
9719cf0
broke the
build!
Commit
9719cf0

21. “...nothing can be
said to be certain,
except death and
taxes”
- Benjamin Franklin
The Build “Tax”
An Empirical Study of Build
Maintenance Effort!
S. McIntosh, B. Adams, T. H. D.
Nguyen, Y. Kamei, A. E. Hassan
[ICSE 2011]
Up to 27% of source
changes require build
changes, too!
11

22. “...nothing can be
said to be certain,
except death and
taxes”
- Benjamin Franklin
The Build “Tax”
An Empirical Study of Build
Maintenance Effort!
S. McIntosh, B. Adams, T. H. D.
Nguyen, Y. Kamei, A. E. Hassan
[ICSE 2011]
Up to 27% of source
changes require build
changes, too!
How do practitioners cope
with build maintenance?
11

23. Cloning!
Useful build
logic
12
Useful build
logic

24. Cloning!
Useful build
logic
12
Copy
&
paste Useful build
logic

25. 13

26. Excessive cloning makes build
maintenance painful
!
!
!
!
!
13

27. Excessive cloning makes build
maintenance painful
!
!
!
!
!
13

28. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
13

29. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
One monolithicbuild system
13

30. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
One monolithicbuild system
1.1 million lines
of build logic
13

31. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
One monolithicbuild system
1.1 million lines
of build logic
Clone coverageof 94%-99%
13

32. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
One monolithicbuild system
1.1 million lines
of build logic
Clone coverageof 94%-99%
Inflation due to cloning of
10x-23x
13

33. Excessive cloning makes build
maintenance painful
!
!
!
!
!
30 custom business
applications
One monolithicbuild system
1.1 million lines
of build logic
Clone coverageof 94%-99%
Inflation due to cloning of
10x-23x
Build changes manuallyduplicated 30 times
13

34. 14

35. 14
How much
cloning is
typical?

36. 14
How much
cloning is
typical?
Measured

37. 14
How much
cloning is
typical?
Measured Typical

38. 14
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
Measured Typical

39. 14
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical

40. 14
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical

41. 15
15

42. 15
Large collection of open source
15

43. 15
Large collection of open source
3,872 projects
15

44. 15
Large collection of open source
3,872 projects
1,275 Java projects
Ant Maven
15

45. 15
Large collection of open source
3,872 projects
2,597 C/C++ projects
Autotools CMake
1,275 Java projects
Ant Maven
15

46. 16
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical

47. Apache Github GNU Sourceforge
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0.00
0.25
0.50
0.75
1.00
Ant Maven Ant Maven Ant Ant Maven
CloneCoverage
Minimum
Length
5
10
15
20
17
Lots of small clones in Java build systems

48. Apache Github GNU Sourceforge
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0.00
0.25
0.50
0.75
1.00
Ant Maven Ant Maven Ant Ant Maven
CloneCoverage
Minimum
Length
5
10
15
20
17
Build logic clonestend to be small
Lots of small clones in Java build systems

49. Apache Github GNU Sourceforge
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0.00
0.25
0.50
0.75
1.00
Ant Maven Ant Maven Ant Ant Maven
CloneCoverage
Minimum
Length
5
10
15
20
17
Half of Maven systems have clone
coverage of at least 47%-50%
Build logic clonestend to be small
Lots of small clones in Java build systems

50. Apache Github GNU Sourceforge
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0.00
0.25
0.50
0.75
1.00
Ant Maven Ant Maven Ant Ant Maven
CloneCoverage
Minimum
Length
5
10
15
20
17
Half of Maven systems have clone
coverage of at least 47%-50%
Build logic clonestend to be small
1/4 of Ant systems have
clone coverage of >50%
Lots of small clones in Java build systems

51. 18
Apache Github GNU Sourceforge
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0.0
0.2
0.4
0.6
Autotools CMake Autotools CMake Autotools CMake Autotools CMake
CloneCoverage
Minimum
Length
5
10
15
20
Less cloning in C/C++ build systems

52. 18
Apache Github GNU Sourceforge
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0.0
0.2
0.4
0.6
Autotools CMake Autotools CMake Autotools CMake Autotools CMake
CloneCoverage
Minimum
Length
5
10
15
20
Less cloning in C/C++ build systems

53. 18
Apache Github GNU Sourceforge
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0.0
0.2
0.4
0.6
Autotools CMake Autotools CMake Autotools CMake Autotools CMake
CloneCoverage
Minimum
Length
5
10
15
20
Less cloning in C/C++ build systems
Clone coverage rarely exceeds
30% in C/C++ build systems

54. 18
Apache Github GNU Sourceforge
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0.0
0.2
0.4
0.6
Autotools CMake Autotools CMake Autotools CMake Autotools CMake
CloneCoverage
Minimum
Length
5
10
15
20
Less cloning in C/C++ build systems
Clone coverage rarely exceeds
30% in C/C++ build systems
Yet there are still someC/C++ build systemswith plenty of clones!27%-66% 21%-48%

55. 19
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical

56. 19
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical>50% clone
coverage
is common
<30% clone
coverage
is common

57. 20
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical>50% clone
coverage
is common
<30% clone
coverage
is common

58. 21

59. Manual analysis of a statistically
representative sample of clones
21

60. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
21

61. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
21

62. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
Sample!
(95%±5%)
382 382 378 349 1,491
21

63. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
Sample!
(95%±5%)
382 382 378 349 1,491
Config.
Const.
Cert.
Pkg.
Depl.
32% 79% 22% 40%
64% 17% 56% 66%
12% 4% 13% 11%
25% 21% 21% 2%
11% 1% 9% 7%
21

64. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
Sample!
(95%±5%)
382 382 378 349 1,491
Config.
Const.
Cert.
Pkg.
Depl.
32% 79% 22% 40%
64% 17% 56% 66%
12% 4% 13% 11%
25% 21% 21% 2%
11% 1% 9% 7%
Cloning shifts from
construction to
configuration
21

65. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
Sample!
(95%±5%)
382 382 378 349 1,491
Config.
Const.
Cert.
Pkg.
Depl.
32% 79% 22% 40%
64% 17% 56% 66%
12% 4% 13% 11%
25% 21% 21% 2%
11% 1% 9% 7%
Cloning shifts from
construction to
configuration
Construction is the
most heavily cloned
C/C++ build phase
21

66. Manual analysis of a statistically
representative sample of clones
Autotools CMakeAnt Maven Total
56,521 71,543 23,723 3,746All clones 155,533
Sample!
(95%±5%)
382 382 378 349 1,491
Config.
Const.
Cert.
Pkg.
Depl.
32% 79% 22% 40%
64% 17% 56% 66%
12% 4% 13% 11%
25% 21% 21% 2%
11% 1% 9% 7%
Cloning shifts from
construction to
configuration
Construction is the
most heavily cloned
C/C++ build phase
Rarely
cloned due
to CPack
21

67. 22
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical>50% clone
coverage
is common
<30% clone
coverage
is common

68. 22
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical Cloning shifts
from const. to
config.
Mostly
construction
clones
>50% clone
coverage
is common
<30% clone
coverage
is common

69. 23
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical Cloning shifts
from const. to
config.
Mostly
construction
clones
>50% clone
coverage
is common
<30% clone
coverage
is common

70. 24
Teams often migrate from one technology to another
Autotools CMakeAnt Maven

71. 24
Teams often migrate from one technology to another
Autotools CMakeAnt Maven
Could technology migration
help to reduce cloning?

72. Migration is not a silver bullet
●
●
●
●
●
●
0.39
0.47
0.52
0.70
0.75
0.82
0.00 0.00
0.04
0.22
0.30
0.47
0.15
0.25
0.36
0.68
0.77
0.84
0.00 0.00 0.00
0.18
0.26
0.39
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Proportion of Systems
CloneCoverage
Abnormality
Very high
High
Moderately high
Normal
Moderately low
Low
Very low
Technology
● Ant
Autotools
CMake
Maven
25

73. Migration is not a silver bullet
●
●
●
●
●
●
0.39
0.47
0.52
0.70
0.75
0.82
0.00 0.00
0.04
0.22
0.30
0.47
0.15
0.25
0.36
0.68
0.77
0.84
0.00 0.00 0.00
0.18
0.26
0.39
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Proportion of Systems
CloneCoverage
Abnormality
Very high
High
Moderately high
Normal
Moderately low
Low
Very low
Technology
● Ant
Autotools
CMake
Maven
25
More cloning in
Maven than Ant

74. Migration is not a silver bullet
●
●
●
●
●
●
0.39
0.47
0.52
0.70
0.75
0.82
0.00 0.00
0.04
0.22
0.30
0.47
0.15
0.25
0.36
0.68
0.77
0.84
0.00 0.00 0.00
0.18
0.26
0.39
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Proportion of Systems
CloneCoverage
Abnormality
Very high
High
Moderately high
Normal
Moderately low
Low
Very low
Technology
● Ant
Autotools
CMake
Maven
25
More cloning in
Maven than Ant
High thresholds!
are very similar

75. Migration is not a silver bullet
●
●
●
●
●
●
0.39
0.47
0.52
0.70
0.75
0.82
0.00 0.00
0.04
0.22
0.30
0.47
0.15
0.25
0.36
0.68
0.77
0.84
0.00 0.00 0.00
0.18
0.26
0.39
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Proportion of Systems
CloneCoverage
Abnormality
Very high
High
Moderately high
Normal
Moderately low
Low
Very low
Technology
● Ant
Autotools
CMake
Maven
25
More cloning in
Maven than Ant
High thresholds!
are very similar
Q: How are they avoidingbuild cloning?

76. 26
Using abstraction mechanisms not!
provided by the build technologies
<!-- Define references to files containing common targets -->
<!DOCTYPE project [
<!ENTITY modules -common SYSTEM "../ modules -common.ent">
]>
...
<project name="bea" default="all">
<!-- Include the file containing common targets. -->
&modules -common;
</project >
Listing 1: Using XML entity expansion to
common build code in the Keel system.

77. 26
Using abstraction mechanisms not!
provided by the build technologies
<!-- Define references to files containing common targets -->
<!DOCTYPE project [
<!ENTITY modules -common SYSTEM "../ modules -common.ent">
]>
...
<project name="bea" default="all">
<!-- Include the file containing common targets. -->
&modules -common;
</project >
Listing 1: Using XML entity expansion to
common build code in the Keel system.
Store an external block ofXML in a macro

78. 26
Using abstraction mechanisms not!
provided by the build technologies
<!-- Define references to files containing common targets -->
<!DOCTYPE project [
<!ENTITY modules -common SYSTEM "../ modules -common.ent">
]>
...
<project name="bea" default="all">
<!-- Include the file containing common targets. -->
&modules -common;
</project >
Listing 1: Using XML entity expansion to
common build code in the Keel system.
Store an external block ofXML in a macro
Expand the macro

79. 27
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical Cloning shifts
from const. to
config.
Mostly
construction
clones
>50% clone
coverage
is common
<30% clone
coverage
is common

80. 27
How much
cloning is
typical?
What type of
logic is being
cloned?
Configuration
details
Packaging
specifications
What can be
done to mitigate
cloning?
Measured Typical Cloning shifts
from const. to
config.
Mostly
construction
clones
Ant Maven
may reduce
cloning
Use of
“creative”
abstraction
>50% clone
coverage
is common
<30% clone
coverage
is common