Separate Sphinx install from setup requirements

Having this in the setup_requires has started to hit issues recently
and separating it seems to be more in line with where Python packaging
is going.

.circleci/config.yml

@@ -20,7 +20,6 @@ references:
         declare -a FILES=(
           "setup.py"
           ".circleci/requirements.txt"
-          "setup-requirements.txt"
           "docs-requirements.txt"
         )
         python3 --version >> .docs-checksum
@@ -38,7 +37,7 @@ references:
       name: Install Dependencies
       command: |
         python3 -m venv venv
-        venv/bin/pip install -r .circleci/requirements.txt -r setup-requirements.txt
+        venv/bin/pip install -r .circleci/requirements.txt
         venv/bin/pip install -r docs-requirements.txt
   save-docs-dependencies-cache: &save-docs-dependencies-cache
     save_cache:
@@ -50,6 +49,7 @@ references:
       name: Build checksum file
       command: |
         declare -a FILES=(
+          "script/docs/requirements.txt"
           "script/linting/requirements.txt"
           "script/typing/requirements.txt"
         )
@@ -65,7 +65,6 @@ references:
         declare -a FILES=(
           "setup.py"
           ".circleci/requirements.txt"
-          "setup-requirements.txt"
           "all-requirements.txt"
         )
         python3 --version >> .checksum
@@ -83,7 +82,7 @@ references:
       name: Install Dependencies
       command: |
         python3 -m venv venv
-        venv/bin/pip install -r .circleci/requirements.txt -r setup-requirements.txt
+        venv/bin/pip install -r .circleci/requirements.txt
         venv/bin/pip install -r all-requirements.txt
   save-dependencies-cache: &save-dependencies-cache
     save_cache:
@@ -138,7 +137,7 @@ jobs:
           name: Build the docs
           command: |
             source venv/bin/activate
-            python setup.py build_sphinx
+            ./script/docs/build.sh
 
   lint:
     <<: *parametrised-python-executor

dev-requirements.txt

@@ -1,4 +1,5 @@
 # Changing this? Also update the CI config which builds an equivalent expanded version.
+-r script/docs/requirements.txt
 -r script/linting/requirements.txt
 -r script/release/requirements.txt
 -r script/typing/requirements.txt

script/docs/build.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+cd $(dirname $(dirname  $(dirname $0)))
+
+exec python setup.py build_sphinx "$@"

script/docs/requirements.txt

@@ -0,0 +1 @@
+../../docs/requirements.txt

setup.py

@@ -3,9 +3,6 @@
 with open('README.rst') as f:
     long_description = f.read()
 
-with open('setup-requirements.txt') as f:
-    setup_requires = f.readlines()
-
 setup(
     name='sr.comp',
     version='1.5.0',
@@ -29,7 +26,6 @@
         'typing-extensions >= 3.7.4.2',
     ],
     python_requires='>=3.7',
-    setup_requires=setup_requires,
     classifiers=[
         'Intended Audience :: Developers',
         'License :: OSI Approved :: GNU General Public License v3 (GPLv3)',