From 41c69f8c876b16e4045f1a1397794b41935321dc Mon Sep 17 00:00:00 2001
From: Martin Duffy <martin.duffy@kitware.com>
Date: Tue, 2 Dec 2025 11:53:11 -0500
Subject: [PATCH] cmGeneratorExpression: Fix parser for adjacent colon and
 comma

Update ParseGeneratorExpression to allow correct parsing of adjacent
colon and comma separators in either order.

Fixes: #27324
---
 Source/cmGeneratorExpressionParser.cxx        | 54 +++++++++----------
 .../LIST-edgecases-check.cmake                |  6 +++
 .../GeneratorExpression/LIST-edgecases.cmake  |  3 ++
 .../GeneratorExpression/RunCMakeTest.cmake    |  1 +
 4 files changed, 35 insertions(+), 29 deletions(-)
 create mode 100644 Tests/RunCMake/GeneratorExpression/LIST-edgecases-check.cmake
 create mode 100644 Tests/RunCMake/GeneratorExpression/LIST-edgecases.cmake

diff --git a/Source/cmGeneratorExpressionParser.cxx b/Source/cmGeneratorExpressionParser.cxx
index c47de3b477..6975642caf 100644
--- a/Source/cmGeneratorExpressionParser.cxx
+++ b/Source/cmGeneratorExpressionParser.cxx
@@ -115,31 +115,9 @@ void cmGeneratorExpressionParser::ParseGeneratorExpression(
       emptyParamTermination = true;
     }
 
-    while (this->it != this->Tokens.end() &&
-           this->it->TokenType == cmGeneratorExpressionToken::CommaSeparator) {
-      commaTokens.push_back(this->it);
-      parameters.resize(parameters.size() + 1);
-      assert(this->it != this->Tokens.end());
-      ++this->it;
-      if (this->it == this->Tokens.end()) {
-        emptyParamTermination = true;
-      }
-    }
-    while (this->it != this->Tokens.end() &&
-           this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator) {
-      extendText(*(parameters.end() - 1), this->it);
-      assert(this->it != this->Tokens.end());
-      ++this->it;
-    }
-    while (this->it != this->Tokens.end() &&
-           this->it->TokenType != cmGeneratorExpressionToken::EndExpression) {
-      this->ParseContent(*(parameters.end() - 1));
-      if (this->it == this->Tokens.end()) {
-        break;
-      }
-      while (this->it != this->Tokens.end() &&
-             this->it->TokenType ==
-               cmGeneratorExpressionToken::CommaSeparator) {
+    auto handleCommaOrColon = [this, &commaTokens, &parameters,
+                               &emptyParamTermination]() -> void {
+      if (this->it->TokenType == cmGeneratorExpressionToken::CommaSeparator) {
         commaTokens.push_back(this->it);
         parameters.resize(parameters.size() + 1);
         assert(this->it != this->Tokens.end());
@@ -147,14 +125,32 @@ void cmGeneratorExpressionParser::ParseGeneratorExpression(
         if (this->it == this->Tokens.end()) {
           emptyParamTermination = true;
         }
-      }
-      while (this->it != this->Tokens.end() &&
-             this->it->TokenType ==
-               cmGeneratorExpressionToken::ColonSeparator) {
+      } else if (this->it->TokenType ==
+                 cmGeneratorExpressionToken::ColonSeparator) {
         extendText(*(parameters.end() - 1), this->it);
         assert(this->it != this->Tokens.end());
         ++this->it;
       }
+    };
+
+    while (
+      this->it != this->Tokens.end() &&
+      (this->it->TokenType == cmGeneratorExpressionToken::CommaSeparator ||
+       this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator)) {
+      handleCommaOrColon();
+    }
+    while (this->it != this->Tokens.end() &&
+           this->it->TokenType != cmGeneratorExpressionToken::EndExpression) {
+      this->ParseContent(*(parameters.end() - 1));
+      if (this->it == this->Tokens.end()) {
+        break;
+      }
+      while (
+        this->it != this->Tokens.end() &&
+        (this->it->TokenType == cmGeneratorExpressionToken::CommaSeparator ||
+         this->it->TokenType == cmGeneratorExpressionToken::ColonSeparator)) {
+        handleCommaOrColon();
+      }
     }
     if (this->it != this->Tokens.end() &&
         this->it->TokenType == cmGeneratorExpressionToken::EndExpression) {
diff --git a/Tests/RunCMake/GeneratorExpression/LIST-edgecases-check.cmake b/Tests/RunCMake/GeneratorExpression/LIST-edgecases-check.cmake
new file mode 100644
index 0000000000..07205f1cae
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/LIST-edgecases-check.cmake
@@ -0,0 +1,6 @@
+file(READ "${RunCMake_TEST_BINARY_DIR}/LIST-edgecases.txt" content)
+
+set(expected "a;b;c:;d\na;b;c;:d")
+if(NOT content STREQUAL expected)
+  set(RunCMake_TEST_FAILED "actual content:\n [[${content}]]\nbut expected:\n [[${expected}]]")
+endif()
diff --git a/Tests/RunCMake/GeneratorExpression/LIST-edgecases.cmake b/Tests/RunCMake/GeneratorExpression/LIST-edgecases.cmake
new file mode 100644
index 0000000000..42b1f7a64b
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/LIST-edgecases.cmake
@@ -0,0 +1,3 @@
+set(ls1 "$<LIST:APPEND,a,b,c:,d>")
+set(ls2 "$<LIST:APPEND,a,b,c,:d>")
+file(GENERATE OUTPUT LIST-edgecases.txt CONTENT ${ls1}\n${ls2})
diff --git a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
index a53cf87a9f..e75b53b88b 100644
--- a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
+++ b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
@@ -56,6 +56,7 @@ run_cmake(FILTER-empty)
 run_cmake(FILTER-InvalidOperator)
 run_cmake(FILTER-Exclude)
 run_cmake(FILTER-Include)
+run_cmake(LIST-edgecases)
 
 function(run_cmake_build test)
   set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${test}-build)