Bug 1704426 - Document supported build hosts. r=glob

Define "build host" support tiers, and their relationship
to existing "target" tiers.

Differential Revision: https://phabricator.services.mozilla.com/D111578

build/docs/supported-configurations.rst

@@ -1,21 +1,87 @@
-Supported build targets
-=======================
+Supported Build Hosts and Targets
+=================================
 
  ..  role:: strikethrough
 
-There are three tiers of **supported Firefox build targets** at this
-time. These tiers represent the shared engineering priorities of the
-Mozilla project.
+There are three tiers of supported Firefox build hosts and targets.
+These tiers represent the shared engineering priorities of the Mozilla project.
+
+The "build host" is the machine that is performing the build of Firefox, and
+the "build target" is the machine that will run the built Firefox application.
+For example, if you were building Firefox for Android on your Linux computer, then the
+Linux computer would be the "build host".
 
 .. note::
 
    Sheriffs are in charge of monitoring the tree. Their definition for tiers
    is for automation jobs, which tells a developer what is expected of them when
-   they land code. This document is about the tiers of supported build targets,
+   they land code. This document is about the tiers of supported build hosts and targets,
    which tells a person compiling/using Firefox what they can expect from Mozilla.
    See the `job tier definition <https://wiki.mozilla.org/Sheriffing/Job_Visibility_Policy#Overview_of_the_Job_Visibility_Tiers>`__ for more information.
 
-.. _tier-1:
+
+.. _build_hosts:
+
+Supported Build Hosts
+---------------------
+
+While we want to help users resolve build-related issues on their systems, we
+are unable to help resolve build system issues on all possible operating
+systems and versions.
+
+Tier-1 Hosts and Toolchains
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Support is available for the following **host operating systems** and versions
+when building for a :ref:`Tier-1 Firefox build target<tier_1_targets>`, including
+cross-compilation where available:
+
+* Ubuntu Linux x86_64
+    * Current stable release
+    * Previous stable release
+    * Current LTS release
+* Debian Linux x86_64
+    * Current stable release
+    * Current testing release
+* Fedora Linux x86_64
+    * Current stable release
+    * Previous stable release
+* macOS Intel and M1
+    * Current release
+    * Previous release
+* Windows x86_64
+    * Windows 10 with MozillaBuild Environment
+
+Tier-2 Hosts and Toolchains
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In addition to the limitations outlined above in the Tier-1 list, our ability
+to provide assistance with build issues using/targeting Tier-2
+hosts/targets/compilers is not unbounded.
+
+While we will endeavour to make a best effort to help resolve issues, you may
+be referred to the relevant community maintainers for further support.
+
+The Tier-2 hosts are:
+
+* Other Linux x86_64 distributions and/or versions
+* Older macOS versions
+* Older Windows x86_64 versions
+
+Tier-3 Hosts and Toolchains
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+We cannot provide any guarantees of assistance in resolving build issues using
+or targeting Tier-3 platforms.
+
+
+Supported Build Targets
+-----------------------
+
+.. _tier_1_targets:
+
+Tier-1 Targets
+^^^^^^^^^^^^^^
 
 The term **"Tier-1 platform"** refers to those platforms - CPU
 architectures and operating systems - that are the primary focus of
@@ -41,7 +107,8 @@ Note also that while Windows/x86 and ARM/AArch64 are supported *as build
 targets*, it is not possible to build Firefox *on* Windows/x86 or
 Windows/AArch64 systems.
 
-.. _tier-2:
+Tier-2 Targets
+^^^^^^^^^^^^^^
 
 **Tier-2 platforms** are actively maintained by the Mozilla community,
 though with less rigorous requirements. Proposed changes resulting in
@@ -60,7 +127,8 @@ The **Tier-2 Firefox platforms** and their supported compilers are:
       require MS COM or the w32api project doesn't expose the necessary
       Windows APIs.*
 
-.. _tier-3:
+Tier-3 Targets
+^^^^^^^^^^^^^^
 
 **Tier-3 platforms** have a maintainer or community which attempt to
 keep the platform working. These platforms are **not supported by our
@@ -71,7 +139,7 @@ outcomes of those tests.
 At any given time a Firefox built from mozilla-central for these
 platforms may or may not work correctly or build at all.
 
-**Tier-3 Firefox platforms** include: 
+**Tier-3 Firefox platforms** include:
 
 -  Linux on various CPU architectures including ARM variants not listed
    above, PowerPC, and x86 CPUs without SSE2 support - maintained by
@@ -93,3 +161,5 @@ proper solution. If you can provide a patch, a regression range or
 assist in verifying that the developer's patches work for your platform,
 that would help a lot towards getting your bugs fixed and checked into
 the tree.
+
+

docs/setup/linux_build.rst

@@ -11,8 +11,9 @@ Requirements
 
 -  **Memory:** 4GB RAM minimum, 8GB+ recommended.
 -  **Disk Space:** At least 30GB of free disk space.
--  **Operating System:** A 64-bit installation of Linux. It is advisable
-   to ensure that your system is fully up-to-date.
+-  **Operating System:** A 64-bit installation of Linux. It is strongly advised
+   that you use a supported distribution; see :ref:`build_hosts`.  We also
+   recommend that your system is fully up-to-date.
 
 .. note::
 

docs/setup/macos_build.rst

@@ -11,8 +11,9 @@ Requirements
 
 -  **Memory:** 4GB RAM minimum, 8GB+ recommended.
 -  **Disk Space:** At least 30GB of free disk space.
--  **Operating System:** macOS 10.12 or later. It is advisable to
-   upgrade to the latest “point” release.
+-  **Operating System:** macOS - most recent or prior release. It is advisable
+   to upgrade to the latest “point” release.  See :ref:`build_hosts` for more
+   information.
 
 
 1. System preparation

docs/setup/windows_build.rst

@@ -15,8 +15,8 @@ Requirements
 
 -  **Memory:** 4GB RAM minimum, 8GB+ recommended.
 -  **Disk Space:** At least 40GB of free disk space.
--  **Operating System:** Windows 7 or later. It is advisable to have
-   Windows Update be fully up-to-date.
+-  **Operating System:** Windows 10. It is advisable to have Windows Update be fully
+   up-to-date. See :ref:`build_hosts` for more information.
 
 1. System preparation
 ---------------------