From da140fba1662e262f05b5e571bf3e6028fc45d86 Mon Sep 17 00:00:00 2001
From: John Vandenberg <jayvdb@gmail.com>
Date: Mon, 11 Jan 2021 15:04:57 +0800
Subject: [PATCH] Partial revert of e4d0d600, fixing #1777 (#1794)

---
 docs/changelog/1777.bugfix.rst   |  1 +
 src/tox/config/__init__.py       |  6 ++++++
 tests/unit/config/test_config.py | 20 ++++++++++++++++++++
 3 files changed, 27 insertions(+)
 create mode 100644 docs/changelog/1777.bugfix.rst

diff --git a/docs/changelog/1777.bugfix.rst b/docs/changelog/1777.bugfix.rst
new file mode 100644
index 0000000000..d938fbae6f
--- /dev/null
+++ b/docs/changelog/1777.bugfix.rst
@@ -0,0 +1 @@
+Fix regression that broke using install_command in config replacements - by :user:`jayvdb`
diff --git a/src/tox/config/__init__.py b/src/tox/config/__init__.py
index 7b91250ed4..0f6fdbe8cc 100644
--- a/src/tox/config/__init__.py
+++ b/src/tox/config/__init__.py
@@ -1848,6 +1848,12 @@ def _replace_match(self, match):
             return os.pathsep
 
         default_value = g["default_value"]
+        # special case: opts and packages. Leave {opts} and
+        # {packages} intact, they are replaced manually in
+        # _venv.VirtualEnv.run_install_command.
+        if sub_value in ("opts", "packages"):
+            return "{{{}}}".format(sub_value)
+
         if sub_value == "posargs":
             return self.reader.getposargs(default_value)
 
diff --git a/tests/unit/config/test_config.py b/tests/unit/config/test_config.py
index 0fd23f4f12..f7fa07b0dd 100644
--- a/tests/unit/config/test_config.py
+++ b/tests/unit/config/test_config.py
@@ -1627,6 +1627,26 @@ def test_install_command_substitutions(self, newconfig):
         ]
         assert envconfig.install_command == expected_deps
 
+    def test_install_command_substitutions_other_section(self, newconfig):
+        config = newconfig(
+            """
+            [base]
+            install_command=some_install --arg={toxinidir}/foo \
+                {envname} {opts} {packages}
+            [testenv]
+            install_command={[base]install_command}
+        """,
+        )
+        envconfig = config.envconfigs["python"]
+        expected_deps = [
+            "some_install",
+            "--arg={}/foo".format(config.toxinidir),
+            "python",
+            "{opts}",
+            "{packages}",
+        ]
+        assert envconfig.install_command == expected_deps
+
     def test_pip_pre(self, newconfig):
         config = newconfig(
             """