[vcpkg] `VCPKG_ENV_PASSTHROUGH_UNTRACKED` (#15115)

* [vcpkg] Add VCPKG_ENV_PASSTHROUGH_UNTRACKED

* [vcpkg] CR comments

Co-authored-by: Robert Schumacher <roschuma@microsoft.com>

7 files changed, 58 insertions, 8 deletions

diff --git a/docs/users/triplets.md b/docs/users/triplets.md
index 9903b197c..37efd590d 100644
--- a/docs/users/triplets.md
+++ b/docs/users/triplets.md
@@ -102,14 +102,20 @@ See the [`"supports"`](../maintainers/manifest-files.md#supports) manifest file
 ### VCPKG_ENV_PASSTHROUGH
 Instructs vcpkg to allow additional environment variables into the build process.
 
-On Windows, vcpkg builds packages in a special clean environment that is isolated from the current command prompt to ensure build reliability and consistency.
-
-This triplet option can be set to a list of additional environment variables that will be added to the clean environment.
+On Windows, vcpkg builds packages in a special clean environment that is isolated from the current command prompt to
+ensure build reliability and consistency. This triplet option can be set to a list of additional environment variables
+that will be added to the clean environment. The values of these environment variables will be hashed into the package
+abi -- to pass through environment variables without abi tracking, see `VCPKG_ENV_PASSTHROUGH_UNTRACKED`.
 
 See also the `vcpkg env` command for how you can inspect the precise environment that will be used.
 
 > Implementers' Note: this list is extracted via the `vcpkg_get_tags` mechanism.
 
+### VCPKG_ENV_PASSTHROUGH_UNTRACKED
+Instructs vcpkg to allow additional environment variables into the build process without abi tracking.
+
+See `VCPKG_ENV_PASSTHROUGH`.
+
 <a name="VCPKG_VISUAL_STUDIO_PATH"></a>
 ### VCPKG_VISUAL_STUDIO_PATH
 Specifies the Visual Studio installation to use.
diff --git a/scripts/azure-pipelines/end-to-end-tests-dir/env-passthrough.ps1 b/scripts/azure-pipelines/end-to-end-tests-dir/env-passthrough.ps1
new file mode 100644
index 000000000..6de1335d7
--- /dev/null
+++ b/scripts/azure-pipelines/end-to-end-tests-dir/env-passthrough.ps1
@@ -0,0 +1,21 @@
+if (-not $IsLinux -and -not $IsMacOS) {

+    . $PSScriptRoot/../end-to-end-tests-prelude.ps1

+

+    $env:_VCPKG_TEST_TRACKED = "a"

+    $env:_VCPKG_TEST_UNTRACKED = "b"

+

+    $x = ./vcpkg "--overlay-triplets=$PSScriptRoot/../../testing/env-passthrough" env "echo %_VCPKG_TEST_TRACKED% %_VCPKG_TEST_TRACKED2% %_VCPKG_TEST_UNTRACKED% %_VCPKG_TEST_UNTRACKED2%"

+    if ($x -ne "%_VCPKG_TEST_TRACKED% %_VCPKG_TEST_TRACKED2% %_VCPKG_TEST_UNTRACKED% %_VCPKG_TEST_UNTRACKED2%")

+    {

+        throw "env should have cleaned the environment ($x)"

+    }

+

+    $y = ./vcpkg "--overlay-triplets=$PSScriptRoot/../../testing/env-passthrough" env --triplet passthrough "echo %_VCPKG_TEST_TRACKED% %_VCPKG_TEST_TRACKED2% %_VCPKG_TEST_UNTRACKED% %_VCPKG_TEST_UNTRACKED2%"

+    if ($y -ne "a %_VCPKG_TEST_TRACKED2% b %_VCPKG_TEST_UNTRACKED2%")

+    {

+        throw "env should have kept the environment ($y)"

+    }

+

+    rm env:_VCPKG_TEST_TRACKED

+    rm env:_VCPKG_TEST_UNTRACKED

+}
\ No newline at end of file
diff --git a/scripts/testing/env-passthrough/passthrough.cmake b/scripts/testing/env-passthrough/passthrough.cmake
new file mode 100644
index 000000000..071b8381e
--- /dev/null
+++ b/scripts/testing/env-passthrough/passthrough.cmake
@@ -0,0 +1,6 @@
+set(VCPKG_TARGET_ARCHITECTURE x64)

+set(VCPKG_CRT_LINKAGE dynamic)

+set(VCPKG_LIBRARY_LINKAGE dynamic)

+

+set(VCPKG_ENV_PASSTHROUGH _VCPKG_TEST_TRACKED _VCPKG_TEST_TRACKED2)

+set(VCPKG_ENV_PASSTHROUGH_UNTRACKED _VCPKG_TEST_UNTRACKED _VCPKG_TEST_UNTRACKED2)

diff --git a/scripts/vcpkg_get_tags.cmake b/scripts/vcpkg_get_tags.cmake
index bec5d9331..749b06e5a 100644
--- a/scripts/vcpkg_get_tags.cmake
+++ b/scripts/vcpkg_get_tags.cmake
@@ -24,6 +24,7 @@ e1e74b5c-18cb-4474-a6bd-5c1c8bc81f3f")
     message("c35112b6-d1ba-415b-aa5d-81de856ef8eb
 VCPKG_PUBLIC_ABI_OVERRIDE=${VCPKG_PUBLIC_ABI_OVERRIDE}
 VCPKG_ENV_PASSTHROUGH=${VCPKG_ENV_PASSTHROUGH}
+VCPKG_ENV_PASSTHROUGH_UNTRACKED=${VCPKG_ENV_PASSTHROUGH_UNTRACKED}
 VCPKG_LOAD_VCVARS_ENV=${VCPKG_LOAD_VCVARS_ENV}
 e1e74b5c-18cb-4474-a6bd-5c1c8bc81f3f
 8c504940-be29-4cba-9f8f-6cd83e9d87b7")
diff --git a/toolsrc/include/vcpkg/build.h b/toolsrc/include/vcpkg/build.h
index 2e3c5fafa..88a12e5c1 100644
--- a/toolsrc/include/vcpkg/build.h
+++ b/toolsrc/include/vcpkg/build.h
@@ -213,6 +213,7 @@ namespace vcpkg::Build
         Optional<ConfigurationType> build_type;
         Optional<std::string> public_abi_override;
         std::vector<std::string> passthrough_env_vars;
+        std::vector<std::string> passthrough_env_vars_tracked;
 
         fs::path toolchain_file() const;
         bool using_vcvars() const;
diff --git a/toolsrc/src/vcpkg/build.cpp b/toolsrc/src/vcpkg/build.cpp
index 4cc4c2987..b01162b4f 100644
--- a/toolsrc/src/vcpkg/build.cpp
+++ b/toolsrc/src/vcpkg/build.cpp
@@ -896,11 +896,13 @@ namespace vcpkg::Build
                                       Hash::Algorithm::Sha1));
         }
 
-        for (const auto& env_var : pre_build_info.passthrough_env_vars)
+        for (const auto& env_var : pre_build_info.passthrough_env_vars_tracked)
         {
-            abi_tag_entries.emplace_back(
-                "ENV:" + env_var,
-                Hash::get_string_hash(System::get_environment_variable(env_var).value_or(""), Hash::Algorithm::Sha1));
+            if (auto e = System::get_environment_variable(env_var))
+            {
+                abi_tag_entries.emplace_back(
+                    "ENV:" + env_var, Hash::get_string_hash(e.value_or_exit(VCPKG_LINE_INFO), Hash::Algorithm::Sha1));
+            }
         }
     }
 
@@ -1305,6 +1307,7 @@ namespace vcpkg::Build
             CHAINLOAD_TOOLCHAIN_FILE,
             BUILD_TYPE,
             ENV_PASSTHROUGH,
+            ENV_PASSTHROUGH_UNTRACKED,
             PUBLIC_ABI_OVERRIDE,
             LOAD_VCVARS_ENV,
         };
@@ -1318,6 +1321,7 @@ namespace vcpkg::Build
             {"VCPKG_CHAINLOAD_TOOLCHAIN_FILE", VcpkgTripletVar::CHAINLOAD_TOOLCHAIN_FILE},
             {"VCPKG_BUILD_TYPE", VcpkgTripletVar::BUILD_TYPE},
             {"VCPKG_ENV_PASSTHROUGH", VcpkgTripletVar::ENV_PASSTHROUGH},
+            {"VCPKG_ENV_PASSTHROUGH_UNTRACKED", VcpkgTripletVar::ENV_PASSTHROUGH_UNTRACKED},
             {"VCPKG_PUBLIC_ABI_OVERRIDE", VcpkgTripletVar::PUBLIC_ABI_OVERRIDE},
             {"VCPKG_LOAD_VCVARS_ENV", VcpkgTripletVar::LOAD_VCVARS_ENV},
         };
@@ -1365,7 +1369,11 @@ namespace vcpkg::Build
                             variable_value);
                     break;
                 case VcpkgTripletVar::ENV_PASSTHROUGH:
-                    passthrough_env_vars = Strings::split(variable_value, ';');
+                    passthrough_env_vars_tracked = Strings::split(variable_value, ';');
+                    Util::Vectors::append(&passthrough_env_vars, passthrough_env_vars_tracked);
+                    break;
+                case VcpkgTripletVar::ENV_PASSTHROUGH_UNTRACKED:
+                    Util::Vectors::append(&passthrough_env_vars, Strings::split(variable_value, ';'));
                     break;
                 case VcpkgTripletVar::PUBLIC_ABI_OVERRIDE:
                     public_abi_override = variable_value.empty() ? nullopt : Optional<std::string>{variable_value};
diff --git a/toolsrc/src/vcpkg/commands.env.cpp b/toolsrc/src/vcpkg/commands.env.cpp
index eadfd5bc0..d05a6ef50 100644
--- a/toolsrc/src/vcpkg/commands.env.cpp
+++ b/toolsrc/src/vcpkg/commands.env.cpp
@@ -75,6 +75,13 @@ namespace vcpkg::Commands::Env
             extra_env.emplace("PYTHONPATH",
                               fs::u8string(paths.installed / fs::u8path(triplet.to_string()) / fs::u8path("python")));
         if (path_vars.size() > 0) extra_env.emplace("PATH", Strings::join(";", path_vars));
+        for (auto&& passthrough : pre_build_info.passthrough_env_vars)
+        {
+            if (auto e = System::get_environment_variable(passthrough))
+            {
+                extra_env.emplace(passthrough, e.value_or_exit(VCPKG_LINE_INFO));
+            }
+        }
 
         auto env = [&] {
             auto clean_env = System::get_modified_clean_environment(extra_env);