Install with --in-tree-build in the tox.ini.

Follows pip's warning message advice, which recommends
trying this option because out-of-tree builds will be
removed.

See: pypa/pip#7555

1 files changed, 9 insertions, 4 deletions

diff --git a/tox.ini b/tox.ini
index d5766b3..0b22f32 100644
--- a/tox.ini
+++ b/tox.ini
@@ -22,9 +22,11 @@ whitelist_externals =
     mkdir
 commands =
     {envpython} -m pip install 'pip>=21.1.1'  # Evade CVE-2021-28363
-    noextra: {envpython} -m pip install {toxinidir}
-    format,perf: {envpython} -m pip install '{toxinidir}[format]'
-    format_nongpl: {envpython} -m pip install '{toxinidir}[format_nongpl]'
+
+    # Remove once pypa/pip#7555 is closed.
+    noextra: {envpython} -m pip install --use-feature=in-tree-build {toxinidir}
+    format,perf: {envpython} -m pip install  --use-feature=in-tree-build '{toxinidir}[format]'
+    format_nongpl: {envpython} -m pip install --use-feature=in-tree-build '{toxinidir}[format_nongpl]'
 
     tests,coverage,codecov: {envpython} -m {env:MAYBE_COVERAGE:} twisted.trial {posargs:jsonschema}
     tests: {envpython} -m doctest {toxinidir}/README.rst
@@ -67,7 +69,10 @@ commands =
 deps = safety
 commands =
     {envpython} -m pip install 'pip>=21.1.1'  # Evade CVE-2021-28363
-    {envpython} -m pip install '{toxinidir}[format]'
+
+    # Remove once pypa/pip#7555 is closed.
+    {envpython} -m pip install --use-feature=in-tree-build '{toxinidir}[format]'
+
     {envpython} -m safety check
 
 [testenv:secrets]