Bug 1377216 - Discover version control info in configure; r=glandium

For reasons unknown to me, Windows CI is periodically failing to find
the Mercurial binary.

In addition, we've also reimplemented various VCS logic throughout
the build system. There is room to cut down on code complexity by
e.g. recording VCS info in configure instead of determining it
at run-time.

Also, for forensic purposes it is sometimes desirable to know which
VCS tool is in use by a build and which version of that tool is being
used.

This commit adds VCS type detection, binary searching, and version
resolution to configure.

substs now contains VCS_CHECKOUT_TYPE, HG, and GIT, which can be
consulted by downstream consumers.

If the Mercurial or Git versions could not be resolved, all variables
are not set. Otherwise, VCS_CHECKOUT_TYPE and one of HG or GIT is set.

If MOZ_AUTOMATION is set, we require that the VCS info be resolved.
This helps prevents weirdness in automation due to unexpected
environment configuration.

MozReview-Commit-ID: AMLy0Hfx5rD

build/moz.configure/init.configure

@@ -309,6 +309,86 @@ def shell(value, mozillabuild):
     return find_program(shell)
 
 
+# Source checkout and version control integration.
+# ================================================
+
+@depends(check_build_environment, 'MOZ_AUTOMATION')
+@checking('for vcs source checkout')
+@imports('os')
+def vcs_checkout_type(build_env, automation):
+    if os.path.exists(os.path.join(build_env.topsrcdir, '.hg')):
+        return 'hg'
+    elif os.path.exists(os.path.join(build_env.topsrcdir, '.git')):
+        return 'git'
+    elif automation:
+        raise FatalCheckError('unable to resolve VCS type; must run '
+                              'from a source checkout when MOZ_AUTOMATION '
+                              'is set')
+
+# Resolve VCS binary for detected repository type.
+hg = check_prog('HG', ('hg',), allow_missing=True,
+                when=depends(vcs_checkout_type)(lambda x: x == 'hg'))
+git = check_prog('GIT', ('git',), allow_missing=True,
+                 when=depends(vcs_checkout_type)(lambda x: x == 'git'))
+
+@depends_if(hg)
+@checking('for Mercurial version')
+@imports('os')
+@imports('re')
+def hg_version(hg):
+    # HGPLAIN in Mercurial 1.5+ forces stable output, regardless of set
+    # locale or encoding.
+    env = dict(os.environ)
+    env['HGPLAIN'] = '1'
+
+    out = check_cmd_output(hg, '--version', env=env)
+
+    match = re.search(r'Mercurial Distributed SCM \(version ([^\)]+)', out)
+
+    if not match:
+        raise FatalCheckError('unable to determine Mercurial version: %s' % out)
+
+    # The version string may be "unknown" for Mercurial run out of its own
+    # source checkout or for bad builds. But LooseVersion handles it.
+
+    return Version(match.group(1))
+
+@depends_if(git)
+@checking('for Git version')
+@imports('re')
+def git_version(git):
+    out = check_cmd_output(git, '--version').rstrip()
+
+    match = re.search('git version (.*)$', out)
+
+    if not match:
+        raise FatalCheckError('unable to determine Git version: %s' % out)
+
+    return Version(match.group(1))
+
+# Only set VCS_CHECKOUT_TYPE if we resolved the VCS binary.
+# Require resolved VCS info when running in automation so automation's
+# environment is more well-defined.
+@depends(vcs_checkout_type, hg_version, git_version, 'MOZ_AUTOMATION')
+def exposed_vcs_checkout_type(vcs_checkout_type, hg, git, automation):
+    if vcs_checkout_type == 'hg':
+        if hg:
+            return 'hg'
+
+        if automation:
+            raise FatalCheckError('could not resolve Mercurial binary info')
+
+    elif vcs_checkout_type == 'git':
+        if git:
+            return 'git'
+
+        if automation:
+            raise FatalCheckError('could not resolve Git binary info')
+    elif vcs_checkout_type:
+        raise FatalCheckError('unhandled VCS type: %s' % vcs_checkout_type)
+
+set_config('VCS_CHECKOUT_TYPE', exposed_vcs_checkout_type)
+
 # Host and target systems
 # ==============================================================
 option('--host', nargs=1, help='Define the system type performing the build')