Avoid consecutive whitespace in rules

1 files changed, 10 insertions, 0 deletions

diff --git a/Source/cmRulePlaceholderExpander.cxx b/Source/cmRulePlaceholderExpander.cxx
index 5ab1b3a..99b0d5c 100644
--- a/Source/cmRulePlaceholderExpander.cxx
+++ b/Source/cmRulePlaceholderExpander.cxx
@@ -334,7 +334,17 @@ void cmRulePlaceholderExpander::ExpandRuleVariables(
       std::string replace =
         this->ExpandRuleVariable(outputConverter, var, replaceValues);
       expandedInput += s.substr(pos, start - pos);
+
+      // Prevent consecutive whitespace in the output if the rule variable
+      // expands to an empty string.
+      bool consecutive = replace.empty() && start > 0 && s[start - 1] == ' ' &&
+        end + 1 < s.size() && s[end + 1] == ' ';
+      if (consecutive) {
+        expandedInput.pop_back();
+      }
+
       expandedInput += replace;
+
       // move to next one
       start = s.find('<', start + var.size() + 2);
       pos = end + 1;