cmConstStack: Factor out of cmListFileBacktrace

This presents value semantics for a stack of constant values.
Internally it shares ownership to avoid copies.  Previously
this was implemented by `cmListFileBacktrace` explicitly,
but the approach can be re-used for other kinds of stacks.

.gitattributes

@@ -36,6 +36,7 @@ configure        eol=lf
 *.hpp            our-c-style
 *.hxx            our-c-style
 *.notcu          our-c-style
+*.tcc            our-c-style
 
 *.cmake          whitespace=tab-in-indent
 *.rst            whitespace=tab-in-indent conflict-marker-size=79

Source/CMakeLists.txt

@@ -182,6 +182,8 @@ set(SRCS
   cmComputeTargetDepends.cxx
   cmConsoleBuf.h
   cmConsoleBuf.cxx
+  cmConstStack.h
+  cmConstStack.tcc
   cmCPackPropertiesGenerator.h
   cmCPackPropertiesGenerator.cxx
   cmCryptoHash.cxx

Source/cmComputeTargetDepends.h

@@ -10,12 +10,12 @@
 #include <vector>
 
 #include "cmGraphAdjacencyList.h"
-#include "cmListFileCache.h"
 
 class cmComputeComponentGraph;
 class cmGeneratorTarget;
 class cmGlobalGenerator;
 class cmLinkItem;
+class cmListFileBacktrace;
 class cmSourceFile;
 class cmTargetDependSet;
 

Source/cmConstStack.h

@@ -0,0 +1,39 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#pragma once
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+#include <memory>
+
+/** Base class template for CRTP to represent a stack of constant values.
+    Provide value semantics, but use efficient reference-counting underneath
+    to avoid copies.  */
+template <typename T, typename Stack>
+class cmConstStack
+{
+  struct Entry;
+  std::shared_ptr<Entry const> TopEntry;
+
+public:
+  /** Default-construct an empty stack.  */
+  cmConstStack();
+
+  /** Get a stack with the given call context added to the top.  */
+  Stack Push(T value) const;
+
+  /** Get a stack with the top level removed.
+      May not be called until after a matching Push.  */
+  Stack Pop() const;
+
+  /** Get the value at the top of the stack.
+      This may be called only if Empty() would return false.  */
+  T const& Top() const;
+
+  /** Return true if this stack is empty.  */
+  bool Empty() const;
+
+protected:
+  cmConstStack(std::shared_ptr<Entry const> parent, T value);
+  cmConstStack(std::shared_ptr<Entry const> top);
+};

Source/cmConstStack.tcc

@@ -0,0 +1,62 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include <cassert>
+#include <memory>
+#include <utility>
+
+template <typename T, typename Stack>
+struct cmConstStack<T, Stack>::Entry
+{
+  Entry(std::shared_ptr<Entry const> parent, T value)
+    : Value(std::move(value))
+    , Parent(std::move(parent))
+  {
+  }
+
+  T Value;
+  std::shared_ptr<Entry const> Parent;
+};
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack() = default;
+
+template <typename T, typename Stack>
+Stack cmConstStack<T, Stack>::Push(T value) const
+{
+  return Stack(this->TopEntry, std::move(value));
+}
+
+template <typename T, typename Stack>
+Stack cmConstStack<T, Stack>::Pop() const
+{
+  assert(this->TopEntry);
+  return Stack(this->TopEntry->Parent);
+}
+
+template <typename T, typename Stack>
+T const& cmConstStack<T, Stack>::Top() const
+{
+  assert(this->TopEntry);
+  return this->TopEntry->Value;
+}
+
+template <typename T, typename Stack>
+bool cmConstStack<T, Stack>::Empty() const
+{
+  return !this->TopEntry;
+}
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack(std::shared_ptr<Entry const> parent,
+                                     T value)
+  : TopEntry(
+      std::make_shared<Entry const>(std::move(parent), std::move(value)))
+{
+}
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack(std::shared_ptr<Entry const> top)
+  : TopEntry(std::move(top))
+{
+}

Source/cmFLTKWrapUICommand.cxx

@@ -10,7 +10,6 @@
 #include "cmCustomCommand.h"
 #include "cmCustomCommandLines.h"
 #include "cmExecutionStatus.h"
-#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
 #include "cmMessageType.h"
@@ -20,6 +19,7 @@
 #include "cmSystemTools.h"
 #include "cmake.h"
 
+class cmListFileBacktrace;
 class cmTarget;
 
 static void FinalAction(cmMakefile& makefile, std::string const& name,

Source/cmInstallCommand.cxx

@@ -35,7 +35,6 @@
 #include "cmInstallRuntimeDependencySetGenerator.h"
 #include "cmInstallScriptGenerator.h"
 #include "cmInstallTargetGenerator.h"
-#include "cmListFileCache.h"
 #include "cmMakefile.h"
 #include "cmMessageType.h"
 #include "cmPolicies.h"
@@ -49,6 +48,8 @@
 #include "cmTargetExport.h"
 #include "cmValue.h"
 
+class cmListFileBacktrace;
+
 namespace {
 
 struct RuntimeDependenciesArgs

Source/cmInstallDirectoryGenerator.cxx

@@ -6,6 +6,7 @@
 
 #include "cmGeneratorExpression.h"
 #include "cmInstallType.h"
+#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
 #include "cmStringAlgorithms.h"

Source/cmInstallDirectoryGenerator.h

@@ -9,9 +9,9 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
+class cmListFileBacktrace;
 class cmLocalGenerator;
 
 /** \class cmInstallDirectoryGenerator

Source/cmInstallExportGenerator.cxx

@@ -15,6 +15,7 @@
 #include "cmExportInstallFileGenerator.h"
 #include "cmExportSet.h"
 #include "cmInstallType.h"
+#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmStringAlgorithms.h"
 #include "cmSystemTools.h"

Source/cmInstallExportGenerator.h

@@ -11,11 +11,11 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
 class cmExportInstallFileGenerator;
 class cmExportSet;
+class cmListFileBacktrace;
 class cmLocalGenerator;
 
 /** \class cmInstallExportGenerator

Source/cmInstallFileSetGenerator.cxx

@@ -11,6 +11,7 @@
 #include "cmGeneratorExpression.h"
 #include "cmGlobalGenerator.h"
 #include "cmInstallType.h"
+#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmStringAlgorithms.h"
 

Source/cmInstallFileSetGenerator.h

@@ -8,11 +8,11 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
 class cmGeneratorTarget;
 class cmFileSet;
+class cmListFileBacktrace;
 class cmLocalGenerator;
 
 class cmInstallFileSetGenerator : public cmInstallGenerator

Source/cmInstallFilesGenerator.cxx

@@ -6,6 +6,7 @@
 
 #include "cmGeneratorExpression.h"
 #include "cmInstallType.h"
+#include "cmListFileCache.h"
 #include "cmStringAlgorithms.h"
 
 class cmLocalGenerator;

Source/cmInstallFilesGenerator.h

@@ -9,9 +9,9 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
+class cmListFileBacktrace;
 class cmLocalGenerator;
 
 /** \class cmInstallFilesGenerator

Source/cmInstallGetRuntimeDependenciesGenerator.cxx

@@ -15,6 +15,7 @@
 
 #include "cmGeneratorExpression.h"
 #include "cmInstallRuntimeDependencySet.h"
+#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
 #include "cmOutputConverter.h"

Source/cmInstallGetRuntimeDependenciesGenerator.h

@@ -7,9 +7,9 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
+class cmListFileBacktrace;
 class cmLocalGenerator;
 class cmInstallRuntimeDependencySet;
 

Source/cmInstallRuntimeDependencySetGenerator.h

@@ -7,10 +7,10 @@
 #include <vector>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 #include "cmScriptGenerator.h"
 
 class cmInstallRuntimeDependencySet;
+class cmListFileBacktrace;
 class cmLocalGenerator;
 
 class cmInstallRuntimeDependencySetGenerator : public cmInstallGenerator

Source/cmInstallSubdirectoryGenerator.cxx

@@ -7,6 +7,7 @@
 #include <utility>
 #include <vector>
 
+#include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
 #include "cmPolicies.h"

Source/cmInstallSubdirectoryGenerator.h

@@ -8,8 +8,8 @@
 #include <string>
 
 #include "cmInstallGenerator.h"
-#include "cmListFileCache.h"
 
+class cmListFileBacktrace;
 class cmLocalGenerator;
 class cmMakefile;
 

Source/cmListFileCache.cxx

@@ -1,8 +1,8 @@
 /* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
    file Copyright.txt or https://cmake.org/licensing for details.  */
+#define cmListFileCache_cxx
 #include "cmListFileCache.h"
 
-#include <cassert>
 #include <memory>
 #include <sstream>
 #include <utility>
@@ -445,53 +445,8 @@ cm::optional<cmListFileContext> cmListFileParser::CheckNesting() const
   return cm::nullopt;
 }
 
-// We hold a call/file context.
-struct cmListFileBacktrace::Entry
-{
-  Entry(std::shared_ptr<Entry const> parent, cmListFileContext lfc)
-    : Context(std::move(lfc))
-    , Parent(std::move(parent))
-  {
-  }
-
-  cmListFileContext Context;
-  std::shared_ptr<Entry const> Parent;
-};
-
-/* NOLINTNEXTLINE(performance-unnecessary-value-param) */
-cmListFileBacktrace::cmListFileBacktrace(std::shared_ptr<Entry const> parent,
-                                         cmListFileContext const& lfc)
-  : TopEntry(std::make_shared<Entry const>(std::move(parent), lfc))
-{
-}
-
-cmListFileBacktrace::cmListFileBacktrace(std::shared_ptr<Entry const> top)
-  : TopEntry(std::move(top))
-{
-}
-
-cmListFileBacktrace cmListFileBacktrace::Push(
-  cmListFileContext const& lfc) const
-{
-  return cmListFileBacktrace(this->TopEntry, lfc);
-}
-
-cmListFileBacktrace cmListFileBacktrace::Pop() const
-{
-  assert(this->TopEntry);
-  return cmListFileBacktrace(this->TopEntry->Parent);
-}
-
-cmListFileContext const& cmListFileBacktrace::Top() const
-{
-  assert(this->TopEntry);
-  return this->TopEntry->Context;
-}
-
-bool cmListFileBacktrace::Empty() const
-{
-  return !this->TopEntry;
-}
+#include "cmConstStack.tcc"
+template class cmConstStack<cmListFileContext, cmListFileBacktrace>;
 
 std::ostream& operator<<(std::ostream& os, cmListFileContext const& lfc)
 {

Source/cmListFileCache.h

@@ -12,6 +12,7 @@
 
 #include <cm/optional>
 
+#include "cmConstStack.h"
 #include "cmSystemTools.h"
 
 /** \class cmListFileCache
@@ -157,35 +158,16 @@ bool operator<(const cmListFileContext& lhs, const cmListFileContext& rhs);
 bool operator==(cmListFileContext const& lhs, cmListFileContext const& rhs);
 bool operator!=(cmListFileContext const& lhs, cmListFileContext const& rhs);
 
-// Represent a backtrace (call stack).  Provide value semantics
-// but use efficient reference-counting underneath to avoid copies.
+// Represent a backtrace (call stack) with efficient value semantics.
 class cmListFileBacktrace
+  : public cmConstStack<cmListFileContext, cmListFileBacktrace>
 {
-public:
-  // Default-constructed backtrace is empty.
-  cmListFileBacktrace() = default;
-
-  // Get a backtrace with the given call context added to the top.
-  cmListFileBacktrace Push(cmListFileContext const& lfc) const;
-
-  // Get a backtrace with the top level removed.
-  // May not be called until after a matching Push.
-  cmListFileBacktrace Pop() const;
-
-  // Get the context at the top of the backtrace.
-  // This may be called only if Empty() would return false.
-  cmListFileContext const& Top() const;
-
-  // Return true if this backtrace is empty.
-  bool Empty() const;
-
-private:
-  struct Entry;
-  std::shared_ptr<Entry const> TopEntry;
-  cmListFileBacktrace(std::shared_ptr<Entry const> parent,
-                      cmListFileContext const& lfc);
-  cmListFileBacktrace(std::shared_ptr<Entry const> top);
+  using cmConstStack::cmConstStack;
+  friend class cmConstStack<cmListFileContext, cmListFileBacktrace>;
 };
+#ifndef cmListFileCache_cxx
+extern template class cmConstStack<cmListFileContext, cmListFileBacktrace>;
+#endif
 
 // Wrap type T as a value with a backtrace.  For purposes of
 // ordering and equality comparison, only the original value is

Source/cmLocalNinjaGenerator.h

@@ -10,7 +10,6 @@
 #include <string>
 #include <vector>
 
-#include "cmListFileCache.h"
 #include "cmLocalCommonGenerator.h"
 #include "cmNinjaTypes.h"
 #include "cmOutputConverter.h"
@@ -21,6 +20,7 @@ class cmGeneratedFileStream;
 class cmGeneratorTarget;
 class cmGlobalGenerator;
 class cmGlobalNinjaGenerator;
+class cmListFileBacktrace;
 class cmMakefile;
 class cmRulePlaceholderExpander;
 class cmake;

Source/cmState.h

@@ -14,7 +14,6 @@
 
 #include "cmDefinitions.h"
 #include "cmLinkedTree.h"
-#include "cmListFileCache.h"
 #include "cmPolicies.h"
 #include "cmProperty.h"
 #include "cmPropertyDefinition.h"
@@ -30,6 +29,11 @@ class cmMakefile;
 class cmStateSnapshot;
 class cmMessenger;
 class cmExecutionStatus;
+class cmListFileBacktrace;
+struct cmListFileArgument;
+
+template <typename T>
+class BT;
 
 class cmState
 {

Source/cmStateDirectory.cxx

@@ -13,6 +13,7 @@
 #include <cmext/string_view>
 
 #include "cmAlgorithms.h"
+#include "cmListFileCache.h"
 #include "cmProperty.h"
 #include "cmPropertyMap.h"
 #include "cmRange.h"

Source/cmStateDirectory.h

@@ -10,11 +10,14 @@
 
 #include "cmAlgorithms.h"
 #include "cmLinkedTree.h"
-#include "cmListFileCache.h"
 #include "cmStatePrivate.h"
 #include "cmStateSnapshot.h"
 #include "cmValue.h"
 
+class cmListFileBacktrace;
+template <typename T>
+class BT;
+
 class cmStateDirectory
 {
   cmStateDirectory(

Utilities/IWYU/mapping.imp

@@ -131,6 +131,9 @@
   { include: [ "<curses.h>", private, "\"cmCursesStandardIncludes.h\"", public ] },
   { include: [ "\"form.h\"", private, "\"cmCursesStandardIncludes.h\"", public ] },
   { include: [ "<form.h>", private, "\"cmCursesStandardIncludes.h\"", public ] },
+
+  # Help IWYU understand our explicit instantiation for cmConstStack.
+  { symbol: [ "cmConstStack::cmConstStack<T, Stack>", private, "\"cmConstStack.h\"", public ] },
 ]
 
 # vim: set ft=toml: