From cb6423703a3c6bbc833047ded4f92ff59ff138aa Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Thu, 16 Oct 2025 13:38:14 -0400
Subject: [PATCH] PrecompileHeaders: downgrade `REUSE_FROM` without a PCH to a
 warning

Prior to f9bc615d (pchreuse: ban PCH reuse from targets which disable
PCH, 2025-06-15), using a target without PCH as a `REUSE_FROM` target
was not an error. Some projects had been doing this unknowingly.
Downgrade the fatal error into a warning so that such projects can at
least continue to build.

Fixes: #27316
---
 Source/cmGeneratorTarget.cxx                              | 8 ++++----
 .../PrecompileHeaders/PchReuseWithoutPch-result.txt       | 1 -
 .../PrecompileHeaders/PchReuseWithoutPch-stderr.txt       | 4 ++--
 3 files changed, 6 insertions(+), 7 deletions(-)
 delete mode 100644 Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-result.txt

diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 5759544fa7..c1cf27a0c0 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -2906,10 +2906,10 @@ cmGeneratorTarget const* cmGeneratorTarget::GetPchReuseTarget() const
   if (generatorTarget) {
     if (generatorTarget->GetPropertyAsBool("DISABLE_PRECOMPILE_HEADERS")) {
       this->Makefile->IssueMessage(
-        MessageType::FATAL_ERROR,
+        MessageType::WARNING,
         cmStrCat(
           "Target \"", *pchReuseFrom, "\" for the \"", this->GetName(),
-          R"(" target's "PRECOMPILE_HEADERS_REUSE_FROM" property has set "DISABLE_PRECOMPILE_HEADERS".)"));
+          R"(" target's "PRECOMPILE_HEADERS_REUSE_FROM" property has set "DISABLE_PRECOMPILE_HEADERS"; ignoring.)"));
       return nullptr;
     }
 
@@ -2959,10 +2959,10 @@ cmGeneratorTarget* cmGeneratorTarget::GetPchReuseTarget()
   if (generatorTarget) {
     if (generatorTarget->GetPropertyAsBool("DISABLE_PRECOMPILE_HEADERS")) {
       this->Makefile->IssueMessage(
-        MessageType::FATAL_ERROR,
+        MessageType::WARNING,
         cmStrCat(
           "Target \"", *pchReuseFrom, "\" for the \"", this->GetName(),
-          R"(" target's "PRECOMPILE_HEADERS_REUSE_FROM" property has set "DISABLE_PRECOMPILE_HEADERS".)"));
+          R"(" target's "PRECOMPILE_HEADERS_REUSE_FROM" property has set "DISABLE_PRECOMPILE_HEADERS"; ignoring.)"));
       return nullptr;
     }
 
diff --git a/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-result.txt b/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-result.txt
deleted file mode 100644
index d00491fd7e..0000000000
--- a/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-stderr.txt b/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-stderr.txt
index 28c69fb98f..fabc459eed 100644
--- a/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-stderr.txt
+++ b/Tests/RunCMake/PrecompileHeaders/PchReuseWithoutPch-stderr.txt
@@ -1,4 +1,4 @@
-CMake Error in CMakeLists\.txt:
+CMake Warning in CMakeLists\.txt:
   Target "pch-generator" for the "reuse_from_nopch" target's
   "PRECOMPILE_HEADERS_REUSE_FROM" property has set
-  "DISABLE_PRECOMPILE_HEADERS".
+  "DISABLE_PRECOMPILE_HEADERS"; ignoring.