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{{admon/important | Comments and Explanations | The page source contains comments providing guidance to fill out each section. They are invisible when viewing this page. To read it, choose the "view source" link.<br/> '''Copy the source to a ''new page'' before making changes!  DO NOT EDIT THIS TEMPLATE FOR YOUR CHANGE PROPOSAL.'''}}
 
 
 
<!-- Self Contained or System Wide Change Proposal?
 
<!-- Self Contained or System Wide Change Proposal?
 
Use this guide to determine to which category your proposed change belongs to.
 
Use this guide to determine to which category your proposed change belongs to.
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<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->
 
<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->
  
= Use update-alternatives for /usr/bin/cc <!-- The name of your change proposal --> =
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= Use update-alternatives for /usr/bin/cc and /usr/bin/c++ <!-- The name of your change proposal --> =
  
 
== Summary ==
 
== Summary ==
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Note that motivation for the change should be in the Motivation section below, and this part should answer the question "What?" rather than "Why?". -->
 
Note that motivation for the change should be in the Motivation section below, and this part should answer the question "What?" rather than "Why?". -->
  
Modify the gcc package so that the /usr/bin/cc symlink is managed by update-alternatives, so that users may update the symlink to point to other compilers.
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Modify the gcc package so that the /usr/bin/cc and /usr/bin/c++ symlinks are managed by update-alternatives.
 
 
 
== Owner ==
 
== Owner ==
 
<!--  
 
<!--  
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== Current status ==
 
== Current status ==
* Targeted release: [[Releases/<number> | Fedora <number> ]]  
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* Targeted release: [[Releases/32 | Fedora 32 ]]  
 
* Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}  
 
* Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}  
 
<!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page  
 
<!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page  
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CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
 
CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
 
-->
 
-->
* Tracker bug: <will be assigned by the Wrangler>
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* Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=1790581 #1790581]
* Release notes tracker: <will be assigned by the Wrangler>
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* Release notes tracker: [https://pagure.io/fedora-docs/release-notes/issue/431 #431]
  
 
== Detailed Description ==
 
== Detailed Description ==
  
 
<!-- Expand on the summary, if appropriate.  A couple sentences suffices to explain the goal, but the more details you can provide the better. -->
 
<!-- Expand on the summary, if appropriate.  A couple sentences suffices to explain the goal, but the more details you can provide the better. -->
 +
 +
The gcc package currently installs symlinks to /usr/bin/cc and /usr/bin/c++ which point to /usr/bin/gcc and /usr/bin/g++ respectively.  For this change, the gcc package will be modified so that update-alternatives creates and manages these symlinks.
 +
 +
In addition to modifying the gcc package, the clang package will be modified so that /usr/bin/clang and /usr/bin/clang++ can be used as alternatives for /usr/bin/cc and /usr/bin/c++.  The clang alternatives will have a lower priority than the gcc alternatives, so that by default, gcc will provide the /usr/bin/cc and /usr/bin/c++ implementations.
 +
 +
The clang package currently has a run-time dependency on gcc, so this ensures that gcc will always provide the default implementation, because it's impossible to install clang without gcc.
 +
 +
The only way users will be able to change the /usr/bin/cc or /usr/bin/c++ implementations will be by explicitly using the update-alternatives tool.
  
 
== Benefit to Fedora ==
 
== Benefit to Fedora ==
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     https://fedoraproject.org/wiki/Changes/perl5.26 (major upgrade to a popular software stack, visible to users of that stack)
 
     https://fedoraproject.org/wiki/Changes/perl5.26 (major upgrade to a popular software stack, visible to users of that stack)
 
-->
 
-->
 +
 +
Many build systems default to using /usr/bin/cc and /usr/bin/c++ as the default C/C++ compilers.  Being able to easily swap out these implementation will provide a lot of flexibility within Fedora for doing things like:
 +
 +
* Setting up alternative buildroots for testing.
 +
* Installing a gcc wrapper script to /usr/bin/cc to help migrate packages to new compiler flags or to capture statistics about compiler usage.
 +
* Letting users experiment easily with alternate compilers.
 +
* Easily switch between system gcc and a development version of gcc.
  
 
== Scope ==
 
== Scope ==
* Proposal owners:
+
* Proposal owners: The proposal owner will implement the necessary changes in the gcc and clang packages.
 
<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 
<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
  
* Other developers: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Other developers: The gcc maintainers will be responsible for reviewing and approving changes to the gcc package. <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 
<!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
  
* Release engineering: [https://pagure.io/releng/issues #Releng issue number] (a check of an impact with Release Engineering is needed) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Release engineering: [https://pagure.io/releng/issues/9120] (a check of an impact with Release Engineering is needed) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)?  Is a mass rebuild required?  include a link to the releng issue.  
 
<!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)?  Is a mass rebuild required?  include a link to the releng issue.  
 
The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing, and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication -->
 
The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing, and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication -->
  
* Policies and guidelines: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Policies and guidelines: No policies or guidelines will need to be updated as a result of this change. <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- Do the packaging guidelines or other documents need to be updated for this feature?  If so, does it need to happen before or after the implementation is done?  If a FPC ticket exists, add a link here. -->
 
<!-- Do the packaging guidelines or other documents need to be updated for this feature?  If so, does it need to happen before or after the implementation is done?  If a FPC ticket exists, add a link here. -->
  
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
N/A (not a System Wide Change)
+
 
 +
This change should not impact upgradeability.
  
 
== How To Test ==
 
== How To Test ==
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
N/A (not a System Wide Change)
+
 
 +
CI tests will be added to the gcc package to ensure that /usr/bin/cc and /usr/bin/c++ still point to /usr/bin/gcc and /usr/bin/g++ when installed.  There will also be a CI test added to the clang package to ensure that /usr/bin/gcc and /usr/bin/g++ remain the default when clang is installed.
  
 
== User Experience ==
 
== User Experience ==
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  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
 
  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
 
-->
 
-->
 +
 +
This change will give users a much better way to experiment using other compilers for their own development.  They will be able to easily switch between different compilers without having to modify their projects build system or make non-standard changes to their Fedora system.
  
 
== Dependencies ==
 
== Dependencies ==
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
N/A (not a System Wide Change)
+
 
 +
This change has no other dependencies besides the changes to the gcc and clang packages.
  
 
== Contingency Plan ==
 
== Contingency Plan ==
  
 
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
 
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Contingency mechanism: (What to do?  Who will do it?) Proposal Owner will revert changes made to gcc and clang packages and rebuild.
 
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
 
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
* Contingency deadline: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+
* Contingency deadline: If the changes are not complete by 2 weeks before the mass rebuild, then we will consider postponing to the next Fedora release and back out any changes that were made. <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
 
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Blocks release? No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Blocks product? product <!-- Applicable for Changes that blocks specific product release/Fedora.next -->
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* Blocks product? None <!-- Applicable for Changes that blocks specific product release/Fedora.next -->
  
 
== Documentation ==
 
== Documentation ==
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
N/A (not a System Wide Change)
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Release notes will be added for this change.
  
 
== Release Notes ==
 
== Release Notes ==
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-->
 
-->
  
[[Category:ChangePageIncomplete]]
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The user /usr/bin/cc and /usr/bin/c++ symlinks are now managed by update-alternatives.  If you would like to change these symlinks to point to another compiler, like clang, for example, you can use these commands:
 +
 
 +
`update-alternatives --set cc /usr/bin/clang`
 +
 
 +
`update-alternatives --set c++ /usr/bin/clang++`
 +
 
 +
[[Category:ChangeAcceptedF32]]
 
<!-- When your change proposal page is completed and ready for review and announcement -->
 
<!-- When your change proposal page is completed and ready for review and announcement -->
 
<!-- remove Category:ChangePageIncomplete and change it to Category:ChangeReadyForWrangler -->
 
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<!-- Select proper category, default is Self Contained Change -->
 
<!-- Select proper category, default is Self Contained Change -->
[[Category:SelfContainedChange]]
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<!--[[Category:SelfContainedChange]]-->
<!-- [[Category:SystemWideChange]] -->
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[[Category:SystemWideChange]]

Latest revision as of 16:50, 13 January 2020


Use update-alternatives for /usr/bin/cc and /usr/bin/c++

Summary

Modify the gcc package so that the /usr/bin/cc and /usr/bin/c++ symlinks are managed by update-alternatives.

Owner

Current status

Detailed Description

The gcc package currently installs symlinks to /usr/bin/cc and /usr/bin/c++ which point to /usr/bin/gcc and /usr/bin/g++ respectively. For this change, the gcc package will be modified so that update-alternatives creates and manages these symlinks.

In addition to modifying the gcc package, the clang package will be modified so that /usr/bin/clang and /usr/bin/clang++ can be used as alternatives for /usr/bin/cc and /usr/bin/c++. The clang alternatives will have a lower priority than the gcc alternatives, so that by default, gcc will provide the /usr/bin/cc and /usr/bin/c++ implementations.

The clang package currently has a run-time dependency on gcc, so this ensures that gcc will always provide the default implementation, because it's impossible to install clang without gcc.

The only way users will be able to change the /usr/bin/cc or /usr/bin/c++ implementations will be by explicitly using the update-alternatives tool.

Benefit to Fedora

Many build systems default to using /usr/bin/cc and /usr/bin/c++ as the default C/C++ compilers. Being able to easily swap out these implementation will provide a lot of flexibility within Fedora for doing things like:

  • Setting up alternative buildroots for testing.
  • Installing a gcc wrapper script to /usr/bin/cc to help migrate packages to new compiler flags or to capture statistics about compiler usage.
  • Letting users experiment easily with alternate compilers.
  • Easily switch between system gcc and a development version of gcc.

Scope

  • Proposal owners: The proposal owner will implement the necessary changes in the gcc and clang packages.
  • Other developers: The gcc maintainers will be responsible for reviewing and approving changes to the gcc package.
  • Release engineering: [1] (a check of an impact with Release Engineering is needed)
  • Policies and guidelines: No policies or guidelines will need to be updated as a result of this change.
  • Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

This change should not impact upgradeability.

How To Test

CI tests will be added to the gcc package to ensure that /usr/bin/cc and /usr/bin/c++ still point to /usr/bin/gcc and /usr/bin/g++ when installed. There will also be a CI test added to the clang package to ensure that /usr/bin/gcc and /usr/bin/g++ remain the default when clang is installed.

User Experience

This change will give users a much better way to experiment using other compilers for their own development. They will be able to easily switch between different compilers without having to modify their projects build system or make non-standard changes to their Fedora system.

Dependencies

This change has no other dependencies besides the changes to the gcc and clang packages.

Contingency Plan

  • Contingency mechanism: (What to do? Who will do it?) Proposal Owner will revert changes made to gcc and clang packages and rebuild.
  • Contingency deadline: If the changes are not complete by 2 weeks before the mass rebuild, then we will consider postponing to the next Fedora release and back out any changes that were made.
  • Blocks release? No
  • Blocks product? None

Documentation

Release notes will be added for this change.

Release Notes

The user /usr/bin/cc and /usr/bin/c++ symlinks are now managed by update-alternatives. If you would like to change these symlinks to point to another compiler, like clang, for example, you can use these commands:

update-alternatives --set cc /usr/bin/clang

update-alternatives --set c++ /usr/bin/clang++