cmLocalGenerator: Refactor `GetIncludeDirectoriesImplicit` method

Use a dedicated `std::set` for implicit include directories instead
of (ab)using the emitted variable.  This in combination with lambdas
makes it easier to comprehend which paths are emitted.

For the implicit include directories we used to omit the
`CMAKE_SYSROOT_COMPILE`/`CMAKE_SYSROOT` prefix.  This has been changed and
the implicit paths are returned prefixed.  Implicit include directory returning
is only ever used by QtAutoGen which requires prefixed paths.  QtAutoGen passes
the (implicit) include paths to the `moc` which isn't aware of
`CMAKE_SYSROOT_COMPILE`/`CMAKE_SYSROOT`.

Source/cmLocalGenerator.cxx

@@ -887,10 +887,21 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
   bool appendAllImplicitDirs) const
 {
   std::vector<BT<std::string>> result;
-
   // Do not repeat an include path.
   std::set<std::string> emitted;
 
+  auto emitDir = [&result, &emitted](std::string const& dir) {
+    if (emitted.insert(dir).second) {
+      result.emplace_back(dir);
+    }
+  };
+
+  auto emitBT = [&result, &emitted](BT<std::string> const& dir) {
+    if (emitted.insert(dir.Value).second) {
+      result.emplace_back(dir);
+    }
+  };
+
   // When automatic include directories are requested for a build then
   // include the source and binary directories at the beginning of the
   // include path to approximate include file behavior for an
@@ -900,21 +911,9 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
   // per-source-file include paths.
   if (this->Makefile->IsOn("CMAKE_INCLUDE_CURRENT_DIR")) {
     // Current binary directory
-    {
-      std::string binDir =
-        this->StateSnapshot.GetDirectory().GetCurrentBinary();
-      if (emitted.insert(binDir).second) {
-        result.emplace_back(std::move(binDir));
-      }
-    }
+    emitDir(this->StateSnapshot.GetDirectory().GetCurrentBinary());
     // Current source directory
-    {
-      std::string srcDir =
-        this->StateSnapshot.GetDirectory().GetCurrentSource();
-      if (emitted.insert(srcDir).second) {
-        result.emplace_back(std::move(srcDir));
-      }
-    }
+    emitDir(this->StateSnapshot.GetDirectory().GetCurrentSource());
   }
 
   if (!target) {
@@ -923,6 +922,11 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
 
   // Implicit include directories
   std::vector<std::string> implicitDirs;
+  std::set<std::string> implicitSet;
+  // Checks if this is not an implicit include directory
+  auto notImplicit = [&implicitSet](std::string const& dir) {
+    return (implicitSet.find(dir) == implicitSet.end());
+  };
   {
     std::string rootPath;
     if (const char* sysrootCompile =
@@ -932,6 +936,7 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
       rootPath = this->Makefile->GetSafeDefinition("CMAKE_SYSROOT");
     }
 
+    // Raw list of implicit include directories
     std::vector<std::string> impDirVec;
 
     // Get platform-wide implicit directories.
@@ -949,12 +954,11 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
     }
 
     for (std::string const& i : impDirVec) {
-      {
-        std::string d = rootPath + i;
-        cmSystemTools::ConvertToUnixSlashes(d);
-        emitted.insert(std::move(d));
+      std::string imd = rootPath + i;
+      cmSystemTools::ConvertToUnixSlashes(imd);
+      if (implicitSet.insert(imd).second) {
+        implicitDirs.emplace_back(std::move(imd));
       }
-      implicitDirs.push_back(i);
     }
   }
 
@@ -967,30 +971,31 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
   if (this->Makefile->IsOn("CMAKE_INCLUDE_DIRECTORIES_PROJECT_BEFORE")) {
     std::string const &topSourceDir = this->GetState()->GetSourceDirectory(),
                       &topBinaryDir = this->GetState()->GetBinaryDirectory();
-    for (BT<std::string> const& i : userDirs) {
+    for (BT<std::string> const& udr : userDirs) {
       // Emit this directory only if it is a subdirectory of the
       // top-level source or binary tree.
-      if (cmSystemTools::ComparePath(i.Value, topSourceDir) ||
-          cmSystemTools::ComparePath(i.Value, topBinaryDir) ||
-          cmSystemTools::IsSubDirectory(i.Value, topSourceDir) ||
-          cmSystemTools::IsSubDirectory(i.Value, topBinaryDir)) {
-        if (emitted.insert(i.Value).second) {
-          result.push_back(i);
+      if (cmSystemTools::ComparePath(udr.Value, topSourceDir) ||
+          cmSystemTools::ComparePath(udr.Value, topBinaryDir) ||
+          cmSystemTools::IsSubDirectory(udr.Value, topSourceDir) ||
+          cmSystemTools::IsSubDirectory(udr.Value, topBinaryDir)) {
+        if (notImplicit(udr.Value)) {
+          emitBT(udr);
         }
       }
     }
   }
 
-  // Construct the final ordered include directory list.
-  for (BT<std::string> const& i : userDirs) {
-    if (emitted.insert(i.Value).second) {
-      result.push_back(i);
+  // Emit remaining non implicit user direcories.
+  for (BT<std::string> const& udr : userDirs) {
+    if (notImplicit(udr.Value)) {
+      emitBT(udr);
     }
   }
 
+  // Sort result
   MoveSystemIncludesToEnd(result, config, lang, target);
 
-  // Add standard include directories for this language.
+  // Append standard include directories for this language.
   {
     std::vector<std::string> userStandardDirs;
     {
@@ -1001,26 +1006,27 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
       cmSystemTools::ExpandListArgument(value, userStandardDirs);
     }
     userDirs.reserve(userDirs.size() + userStandardDirs.size());
-    for (std::string& d : userStandardDirs) {
-      cmSystemTools::ConvertToUnixSlashes(d);
-      result.emplace_back(d);
-      userDirs.emplace_back(std::move(d));
+    for (std::string& usd : userStandardDirs) {
+      cmSystemTools::ConvertToUnixSlashes(usd);
+      if (notImplicit(usd)) {
+        emitDir(usd);
+      }
+      userDirs.emplace_back(std::move(usd));
     }
   }
 
+  // Append compiler implicit include directories
   if (!stripImplicitDirs) {
-    // Append only implicit directories that were requested by the user
-    for (std::string const& i : implicitDirs) {
-      if (std::find(userDirs.begin(), userDirs.end(), i) != userDirs.end()) {
-        result.emplace_back(i);
+    // Append implicit directories that were requested by the user only
+    for (BT<std::string> const& udr : userDirs) {
+      if (!notImplicit(udr.Value)) {
+        emitBT(udr);
       }
     }
-    // Append remaining implicit directories on demand
+    // Append remaining implicit directories (on demand)
     if (appendAllImplicitDirs) {
-      for (std::string const& i : implicitDirs) {
-        if (std::find(result.begin(), result.end(), i) == result.end()) {
-          result.emplace_back(i);
-        }
+      for (std::string& imd : implicitDirs) {
+        emitDir(imd);
       }
     }
   }