Reinstate ProgramOptionEnv.parse_environment

tests/unit-tests/options/test_program_option.cpp

@@ -209,6 +209,50 @@ TEST_F(ProgramOption, unparsed_command_line_returns_unprocessed_tokens)
     EXPECT_THAT(po.unparsed_command_line(), ElementsAre("--hello", "world", "--answer", "42"));
 }
 
+TEST(ProgramOptionEnv, parse_environment)
+{
+    // Env variables should be uppercase and "_" delimited
+    char const* name = "some-key";
+    char const* key = "SOME_KEY";
+    char const* value = "test_value";
+    auto const prefix = std::string{__PRETTY_FUNCTION__} + "_";
+
+    auto const mapper = [&prefix](std::string const& from) -> std::string
+    {
+        if (from.starts_with(prefix))
+        {
+            auto result = from.substr(prefix.size());
+
+            for(auto& ch : result)
+            {
+                if (ch == '_') ch = '-';
+                else ch = std::tolower(ch, std::locale::classic());
+            }
+
+            return result;
+        }
+        else
+        {
+            return std::string{};
+        }
+    };
+
+    auto const env = prefix + key;
+    setenv(env.c_str(), value, true);
+
+    bpo::options_description desc;
+    desc.add_options()
+        (name, bpo::value<std::string>());
+
+    mir::options::ProgramOption po;
+    po.parse_environment(desc, mapper);
+
+    EXPECT_EQ(value, po.get(name, "default"));
+    EXPECT_EQ("default", po.get("garbage", "default"));
+    EXPECT_TRUE(po.is_set(name));
+    EXPECT_FALSE(po.is_set("garbage"));
+}
+
 // TODO need to parse something
 TEST(ProgramOptionFile, parse_files)
 {