cmRulePlaceholderExpander: add base class for placeholder expansion reuse

1 files changed, 54 insertions, 0 deletions

diff --git a/Source/cmPlaceholderExpander.cxx b/Source/cmPlaceholderExpander.cxx
new file mode 100644
index 0000000..118017e
--- /dev/null
+++ b/Source/cmPlaceholderExpander.cxx
@@ -0,0 +1,54 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#include "cmPlaceholderExpander.h"
+
+#include <cctype>
+
+std::string& cmPlaceholderExpander::ExpandVariables(std::string& s)
+{
+  std::string::size_type start = s.find('<');
+  // no variables to expand
+  if (start == std::string::npos) {
+    return s;
+  }
+  std::string::size_type pos = 0;
+  std::string expandedInput;
+  while (start != std::string::npos && start < s.size() - 2) {
+    std::string::size_type end = s.find('>', start);
+    // if we find a < with no > we are done
+    if (end == std::string::npos) {
+      s = expandedInput;
+      return s;
+    }
+    char c = s[start + 1];
+    // if the next char after the < is not A-Za-z then
+    // skip it and try to find the next < in the string
+    if (!isalpha(c)) {
+      start = s.find('<', start + 1);
+    } else {
+      // extract the var
+      std::string var = s.substr(start + 1, end - start - 1);
+      std::string replace = this->ExpandVariable(var);
+      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;
+    }
+  }
+  // add the rest of the input
+  expandedInput += s.substr(pos, s.size() - pos);
+  s = expandedInput;
+
+  return s;
+}