Make dotnet --info print all DOTNET_* environment variables (#117797)

`dotnet --info` currently only prints `DOTNET_ROOT` / `DOTNET_ROOT_<ARCH>` if they are set. Expand it to all environment variables with a `DOTNET_` prefix. Also add a line about detecting COMPlus_* variables.

Example:
```
Environment variables:
  DOTNET_ROLL_FORWARD                      [Major]
  DOTNET_ROOT                              [C:\repos\runtime\.dotnet]
  DOTNET_SKIP_FIRST_TIME_EXPERIENCE        [1]
  Detected COMPlus_* environment variable(s). Consider transitioning to DOTNET_* equivalent.
```

Author: elinor-fung

src/installer/tests/HostActivation.Tests/HostCommands.cs

@@ -83,6 +83,91 @@ public void Info_Utf8Path()
                 .And.HaveStdOutMatching($@"DOTNET_ROOT.*{installLocation}");
         }
 
+        [Fact]
+        public void Info_ListEnvironment()
+        {
+            var command = TestContext.BuiltDotNet.Exec("--info")
+                .CaptureStdOut();
+
+            // Add DOTNET_ROOT environment variables
+            (string Architecture, string Path)[] dotnetRootEnvVars = [
+                ("arm64", "/arm64/dotnet/root"),
+                ("x64", "/x64/dotnet/root"),
+                ("x86", "/x86/dotnet/root"),
+                ("unknown", "/unknown/dotnet/root")
+            ];
+            foreach (var envVar in dotnetRootEnvVars)
+            {
+                command = command.DotNetRoot(envVar.Path, envVar.Architecture);
+            }
+
+            string dotnetRootNoArch = "/dotnet/root";
+            command = command.DotNetRoot(dotnetRootNoArch);
+
+            // Add additional DOTNET_* environment variables
+            (string Name, string Value)[] envVars = [
+                ("DOTNET_ROLL_FORWARD", "Major"),
+                ("DOTNET_SOME_SETTING", "/some/setting"),
+                ("DOTNET_HOST_TRACE", "1")
+            ];
+
+            (string Name, string Value)[] differentCaseEnvVars = [
+                ("dotnet_env_var", "dotnet env var value"),
+                ("dOtNeT_setting", "doOtNeT setting value"),
+            ];
+            foreach ((string name, string value) in envVars.Concat(differentCaseEnvVars))
+            {
+                command = command.EnvironmentVariable(name, value);
+            }
+
+            string otherEnvVar = "OTHER";
+            command = command.EnvironmentVariable(otherEnvVar, "value");
+
+            var result = command.Execute();
+            result.Should().Pass()
+                .And.HaveStdOutContaining("Environment variables:")
+                .And.HaveStdOutMatching($@"{Constants.DotnetRoot.EnvironmentVariable}\s*\[{dotnetRootNoArch}\]")
+                .And.NotHaveStdOutContaining(otherEnvVar);
+
+            foreach ((string architecture, string path) in dotnetRootEnvVars)
+            {
+                result.Should()
+                    .HaveStdOutMatching($@"{Constants.DotnetRoot.ArchitectureEnvironmentVariablePrefix}{architecture.ToUpper()}\s*\[{path}\]");
+            }
+
+            foreach ((string name, string value) in envVars)
+            {
+                result.Should().HaveStdOutMatching($@"{name}\s*\[{value}\]");
+            }
+
+            foreach ((string name, string value) in differentCaseEnvVars)
+            {
+                if (OperatingSystem.IsWindows())
+                {
+                    // Environment variables are case-insensitive on Windows
+                    result.Should().HaveStdOutMatching($@"{name}\s*\[{value}\]");
+                }
+                else
+                {
+                    result.Should().NotHaveStdOutContaining(name);
+                }
+            }
+        }
+
+        [Fact]
+        public void Info_ListEnvironment_LegacyPrefixDetection()
+        {
+            string comPlusEnvVar = "COMPlus_ReadyToRun";
+            TestContext.BuiltDotNet.Exec("--info")
+                .EnvironmentVariable(comPlusEnvVar, "0")
+                .CaptureStdOut()
+                .Execute()
+                .Should().Pass()
+                .And.HaveStdOutContaining("Environment variables:")
+                .And.NotHaveStdOutContaining(comPlusEnvVar)
+                .And.HaveStdOutContaining("Detected COMPlus_* environment variable(s). Consider transitioning to DOTNET_* equivalent.");
+        }
+
         [Fact]
         public void ListRuntimes()
         {

src/installer/tests/HostActivation.Tests/InstallLocation.cs

@@ -121,42 +121,6 @@ public void EnvironmentVariable_DotnetRootPathExistsButHasNoHost()
                 .And.HaveStdErrContaining($"The required library {Binaries.HostFxr.FileName} could not be found.");
         }
 
-        [Fact]
-        public void EnvironmentVariable_DotNetInfo_ListEnvironment()
-        {
-            var command = TestContext.BuiltDotNet.Exec("--info")
-                .CaptureStdOut();
-
-            var envVars = new (string Architecture, string Path)[] {
-                ("arm64", "/arm64/dotnet/root"),
-                ("x64", "/x64/dotnet/root"),
-                ("x86", "/x86/dotnet/root")
-            };
-            foreach(var envVar in envVars)
-            {
-                command = command.DotNetRoot(envVar.Path, envVar.Architecture);
-            }
-
-            string dotnetRootNoArch = "/dotnet/root";
-            command = command.DotNetRoot(dotnetRootNoArch);
-
-            (string Architecture, string Path) unknownEnvVar = ("unknown", "/unknown/dotnet/root");
-            command = command.DotNetRoot(unknownEnvVar.Path, unknownEnvVar.Architecture);
-
-            var result = command.Execute();
-            result.Should().Pass()
-                .And.HaveStdOutContaining("Environment variables:")
-                .And.HaveStdOutMatching($@"{Constants.DotnetRoot.EnvironmentVariable}\s*\[{dotnetRootNoArch}\]")
-                .And.NotHaveStdOutContaining($"{Constants.DotnetRoot.ArchitectureEnvironmentVariablePrefix}{unknownEnvVar.Architecture.ToUpper()}")
-                .And.NotHaveStdOutContaining($"[{unknownEnvVar.Path}]");
-
-            foreach ((string architecture, string path) in envVars)
-            {
-                result.Should()
-                    .HaveStdOutMatching($@"{Constants.DotnetRoot.ArchitectureEnvironmentVariablePrefix}{architecture.ToUpper()}\s*\[{path}\]");
-            }
-        }
-
         [Fact]
         public void DefaultInstallLocation()
         {

src/native/corehost/fxr/install_info.cpp

@@ -6,29 +6,47 @@
 #include "trace.h"
 #include "utils.h"
 
+#include <algorithm>
+#include <vector>
+
 bool install_info::print_environment(const pal::char_t* leading_whitespace)
 {
-    bool found_any = false;
-
-    const pal::char_t* fmt = _X("%s%-17s [%s]");
-    pal::string_t value;
-    if (pal::getenv(DOTNET_ROOT_ENV_VAR, &value))
-    {
-        found_any = true;
-        trace::println(fmt, leading_whitespace, DOTNET_ROOT_ENV_VAR, value.c_str());
-    }
-
-    for (uint32_t i = 0; i < static_cast<uint32_t>(pal::architecture::__last); ++i)
+    // Enumerate environment variables and filter for DOTNET_
+    std::vector<std::pair<pal::string_t, pal::string_t>> env_vars;
+    bool found_complus_var = false;
+    pal::enumerate_environment_variables([&](const pal::char_t* name, const pal::char_t* value)
     {
-        pal::string_t env_var = get_dotnet_root_env_var_for_arch(static_cast<pal::architecture>(i));
-        if (pal::getenv(env_var.c_str(), &value))
+        // Check if the environment variable starts with DOTNET_
+#if defined(TARGET_WINDOWS)
+        // Environment variables are case-insensitive on Windows
+        auto comp_func = pal::strncasecmp;
+#else
+        auto comp_func = pal::strncmp;
+#endif
+        if (comp_func(name, _X("DOTNET_"), STRING_LENGTH("DOTNET_")) == 0)
         {
-            found_any = true;
-            trace::println(fmt, leading_whitespace, env_var.c_str(), value.c_str());
+            env_vars.push_back(std::make_pair(name, value));
         }
+        else if (!found_complus_var && comp_func(name, _X("COMPlus_"), STRING_LENGTH("COMPlus_")) == 0)
+        {
+            found_complus_var = true;
+        }
+    });
+
+    // Sort for consistent output
+    std::sort(env_vars.begin(), env_vars.end());
+
+    // Print all relevant environment variables
+    const pal::char_t* fmt = _X("%s%-40s [%s]");
+    for (const auto& env_var : env_vars)
+    {
+        trace::println(fmt, leading_whitespace, env_var.first.c_str(), env_var.second.c_str());
     }
 
-    return found_any;
+    if (found_complus_var)
+        trace::println(_X("%sDetected COMPlus_* environment variable(s). Consider transitioning to DOTNET_* equivalent."), leading_whitespace);
+
+    return env_vars.size() > 0 || found_complus_var;
 }
 
 bool install_info::try_get_install_location(pal::architecture arch, pal::string_t& out_install_location, bool* out_is_registered)

src/native/corehost/hostmisc/pal.h

@@ -17,6 +17,7 @@
 #include <memory>
 #include <algorithm>
 #include <cassert>
+#include <functional>
 
 #if defined(_WIN32)
 
@@ -305,6 +306,7 @@ namespace pal
     bool get_module_path(dll_t mod, string_t* recv);
     bool get_current_module(dll_t* mod);
     bool getenv(const char_t* name, string_t* recv);
+    void enumerate_environment_variables(const std::function<void(const char_t*, const char_t*)> callback);
     bool get_default_servicing_directory(string_t* recv);
 
     enum class architecture

src/native/corehost/hostmisc/pal.unix.cpp

@@ -957,6 +957,24 @@ bool pal::getenv(const pal::char_t* name, pal::string_t* recv)
     return (recv->length() > 0);
 }
 
+extern char **environ;
+void pal::enumerate_environment_variables(const std::function<void(const pal::char_t*, const pal::char_t*)> callback)
+{
+    if (environ == nullptr)
+        return;
+
+    for (char **env = environ; *env != nullptr; ++env)
+    {
+        const char* current = *env;
+        const char* separator = ::strchr(current, '=');
+        if (separator != nullptr && separator != current)
+        {
+            pal::string_t name(current, separator - current);
+            callback(name.c_str(), separator + 1);
+        }
+    }
+}
+
 bool pal::fullpath(pal::string_t* path, bool skip_error_logging)
 {
     return realpath(path, skip_error_logging);

src/native/corehost/hostmisc/pal.windows.cpp

@@ -714,6 +714,28 @@ bool pal::getenv(const char_t* name, string_t* recv)
     return true;
 }
 
+void pal::enumerate_environment_variables(const std::function<void(const pal::char_t*, const pal::char_t*)> callback)
+{
+    LPWCH env_strings = ::GetEnvironmentStringsW();
+    if (env_strings == nullptr)
+        return;
+
+    LPWCH current = env_strings;
+    while (*current != L'\0')
+    {
+        LPWCH eq_ptr = ::wcschr(current, L'=');
+        if (eq_ptr != nullptr && eq_ptr != current)
+        {
+            pal::string_t name(current, eq_ptr - current);
+            callback(name.c_str(), eq_ptr + 1);
+        }
+
+        current += pal::strlen(current) + 1; // Move to next string
+    }
+
+    ::FreeEnvironmentStringsW(env_strings);
+}
+
 int pal::xtoi(const char_t* input)
 {
     return ::_wtoi(input);