From 69f95cf1d93945ace09ee9a87c0185b1ee6e4a47 Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Tue, 26 Oct 2021 12:51:44 -0400
Subject: cmCTestRunTest: fix modifying non-existent envvars

When appending or modifying to a variable that has not been modified
before, the iterator was not valid, but it was used to insert into the
map again. Instead, just use indexing into the map since we know it will
exist by the end of the function anyways.

Fixes: #22796
---
 Source/CTest/cmCTestRunTest.cxx   |  8 ++------
 Tests/Environment/CMakeLists.txt  | 18 ++++++++++++++++++
 Tests/Environment/check_mod.cmake |  8 +++++++-
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/Source/CTest/cmCTestRunTest.cxx b/Source/CTest/cmCTestRunTest.cxx
index 20f0ed3..2d1562a 100644
--- a/Source/CTest/cmCTestRunTest.cxx
+++ b/Source/CTest/cmCTestRunTest.cxx
@@ -800,13 +800,9 @@ bool cmCTestRunTest::ForkProcess(
     auto apply_diff =
       [&env_application](const std::string& name,
                          std::function<void(std::string&)> const& apply) {
-        auto entry = env_application.find(name);
-        std::string output;
-        if (entry != env_application.end() && entry->second) {
-          output = *entry->second;
-        }
+        std::string output = env_application[name].value_or(std::string{});
         apply(output);
-        entry->second = output;
+        env_application[name] = output;
       };
 
     bool err_occurred = false;
diff --git a/Tests/Environment/CMakeLists.txt b/Tests/Environment/CMakeLists.txt
index 17009bd..5f1edbf 100644
--- a/Tests/Environment/CMakeLists.txt
+++ b/Tests/Environment/CMakeLists.txt
@@ -45,6 +45,12 @@ set_property(TEST EchoEnvironment3
     "STRING_MANIP=string_append:suffix"
     "STRING_MANIP=string_prepend:prefix"
 
+    # String manipulation on non-existent.
+    "STRING_DNE=string_append:post-"
+    "STRING_DNE=string_prepend:-pre"
+    "STRING_DNE=string_append:suffix"
+    "STRING_DNE=string_prepend:prefix"
+
     # Path manipulation.
     "PATH_MANIP=set:core"
     "PATH_MANIP=path_list_append:post"
@@ -52,10 +58,22 @@ set_property(TEST EchoEnvironment3
     "PATH_MANIP=path_list_append:suffix"
     "PATH_MANIP=path_list_prepend:prefix"
 
+    # Path manipulation on non-existent.
+    "PATH_DNE=path_list_append:post"
+    "PATH_DNE=path_list_prepend:pre"
+    "PATH_DNE=path_list_append:suffix"
+    "PATH_DNE=path_list_prepend:prefix"
+
     # CMake list manipulation.
     "CMAKE_LIST_MANIP=set:core"
     "CMAKE_LIST_MANIP=cmake_list_append:post"
     "CMAKE_LIST_MANIP=cmake_list_prepend:pre"
     "CMAKE_LIST_MANIP=cmake_list_append:suffix"
     "CMAKE_LIST_MANIP=cmake_list_prepend:prefix"
+
+    # CMake list manipulation on non-existent.
+    "CMAKE_LIST_DNE=cmake_list_append:post"
+    "CMAKE_LIST_DNE=cmake_list_prepend:pre"
+    "CMAKE_LIST_DNE=cmake_list_append:suffix"
+    "CMAKE_LIST_DNE=cmake_list_prepend:prefix"
 )
diff --git a/Tests/Environment/check_mod.cmake b/Tests/Environment/check_mod.cmake
index 16d02f2..179bd7a 100644
--- a/Tests/Environment/check_mod.cmake
+++ b/Tests/Environment/check_mod.cmake
@@ -20,12 +20,18 @@ set(expect_DIRECT "new")
 set(expect_STRING_MANIP "prefix-pre-core-post-suffix")
 set(expect_PATH_MANIP "prefix${path_sep}pre${path_sep}core${path_sep}post${path_sep}suffix")
 set(expect_CMAKE_LIST_MANIP "prefix;pre;core;post;suffix")
+set(expect_STRING_DNE "prefix-prepost-suffix")
+set(expect_PATH_DNE "prefix${path_sep}pre${path_sep}post${path_sep}suffix")
+set(expect_CMAKE_LIST_DNE "prefix;pre;post;suffix")
 
 set(expected_vars
   DIRECT
   STRING_MANIP
   PATH_MANIP
-  CMAKE_LIST_MANIP)
+  CMAKE_LIST_MANIP
+  STRING_DNE
+  PATH_DNE
+  CMAKE_LIST_DNE)
 
 while (out)
   string(FIND "${out}" "\n" nl_pos)
-- 
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