install(PACKAGE_INFO): Export required components

Modify cmExportPackageInfoGenerator to record not just what packages are
required, but what targets (components) are used by those requirements,
and to populate the requirements' component lists accordingly.

Source/cmExportPackageInfoGenerator.cxx

@@ -127,9 +127,22 @@ void cmExportPackageInfoGenerator::GeneratePackageRequires(
 {
   if (!this->Requirements.empty()) {
     Json::Value& requirements = package["requires"];
+
+    // Build description for each requirement.
     for (auto const& requirement : this->Requirements) {
+      auto data = Json::Value{ Json::objectValue };
+
+      // Add required components.
+      if (!requirement.second.empty()) {
+        auto components = Json::Value{ Json::arrayValue };
+        for (std::string const& component : requirement.second) {
+          components.append(component);
+        }
+        data["components"] = components;
+      }
+
       // TODO: version, hint
-      requirements[requirement] = Json::Value{};
+      requirements[requirement.first] = data;
     }
   }
 }
@@ -257,10 +270,10 @@ bool cmExportPackageInfoGenerator::NoteLinkedTarget(
       return false;
     }
 
+    std::string component = linkedName.substr(prefix.length());
+    this->LinkTargets.emplace(linkedName, cmStrCat(pkgName, ':', component));
     // TODO: Record package version, hint.
-    this->Requirements.emplace(pkgName);
-    this->LinkTargets.emplace(
-      linkedName, cmStrCat(pkgName, ':', linkedName.substr(prefix.length())));
+    this->Requirements[pkgName].emplace(std::move(component));
     return true;
   }
 
@@ -278,16 +291,13 @@ bool cmExportPackageInfoGenerator::NoteLinkedTarget(
       return false;
     }
 
-    auto pkgName =
-      cm::string_view{ linkNamespace.data(), linkNamespace.size() - 2 };
-
+    std::string pkgName{ linkNamespace.data(), linkNamespace.size() - 2 };
+    std::string component = linkedTarget->GetExportName();
     if (pkgName == this->GetPackageName()) {
-      this->LinkTargets.emplace(linkedName,
-                                cmStrCat(':', linkedTarget->GetExportName()));
+      this->LinkTargets.emplace(linkedName, cmStrCat(':', component));
     } else {
-      this->Requirements.emplace(pkgName);
-      this->LinkTargets.emplace(
-        linkedName, cmStrCat(pkgName, ':', linkedTarget->GetExportName()));
+      this->LinkTargets.emplace(linkedName, cmStrCat(pkgName, ':', component));
+      this->Requirements[pkgName].emplace(std::move(component));
     }
     return true;
   }

Source/cmExportPackageInfoGenerator.h

@@ -110,5 +110,5 @@ private:
   std::vector<std::string> DefaultConfigurations;
 
   std::map<std::string, std::string> LinkTargets;
-  std::set<std::string> Requirements;
+  std::map<std::string, std::set<std::string>> Requirements;
 };

Tests/RunCMake/PackageInfo/Requirements-check.cmake

@@ -8,8 +8,10 @@ expect_value("${content}" "interface" "components" "libb" "type")
 
 file(READ "${out_dir}/bar.cps" content)
 expect_value("${content}" "bar" "name")
-expect_null("${content}" "requires" "foo")
-expect_null("${content}" "requires" "test")
+expect_array("${content}"      1 "requires"  "foo" "components")
+expect_value("${content}" "libb" "requires"  "foo" "components" 0)
+expect_array("${content}"      1 "requires" "test" "components")
+expect_value("${content}" "liba" "requires" "test" "components" 0)
 expect_value("${content}" "interface" "components" "libc" "type")
 expect_value("${content}" "interface" "components" "libd" "type")