Fix --keep-going to exit with nonzero if a failure occurred (#670)

* Fix --keep-going to exit with nonzero if a failure occurred

* PR comments

azure-pipelines/end-to-end-tests-dir/keep-going.ps1

@@ -0,0 +1,9 @@
+. $PSScriptRoot/../end-to-end-tests-prelude.ps1
+
+# Test keep-going to not report an error
+Run-Vcpkg -TestArgs ($commonArgs + @("install", "vcpkg-empty-port", "--keep-going"))
+Throw-IfFailed
+
+# Test keep-going to report an error
+Run-Vcpkg -TestArgs ($commonArgs + @("install", "vcpkg-fail-if-depended-upon", "--keep-going"))
+Throw-IfNotFailed

include/vcpkg/install.h

@@ -48,6 +48,7 @@ namespace vcpkg
 
         void print() const;
         std::string xunit_results() const;
+        bool failed() const;
     };
 
     struct InstallDir

src/vcpkg/install.cpp

@@ -431,6 +431,18 @@ namespace vcpkg
         }
     }
 
+    bool InstallSummary::failed() const
+    {
+        for (const auto& result : this->results)
+        {
+            if (result.build_result.value_or_exit(VCPKG_LINE_INFO).code != BuildResult::SUCCEEDED)
+            {
+                return true;
+            }
+        }
+        return false;
+    }
+
     struct TrackedPackageInstallGuard
     {
         SpecSummary* current_summary = nullptr;
@@ -1209,13 +1221,14 @@ namespace vcpkg
             {
                 if (!result.is_user_requested_install()) continue;
                 auto bpgh = result.get_binary_paragraph();
-                assert(bpgh);
+                // If a package failed to build, don't attempt to print usage.
+                // e.g. --keep-going
                 if (!bpgh) continue;
                 Install::print_usage_information(*bpgh, printed_usages, fs, paths.installed());
             }
         }
 
-        Checks::exit_success(VCPKG_LINE_INFO);
+        Checks::exit_with_code(VCPKG_LINE_INFO, summary.failed());
     }
 
     void InstallCommand::perform_and_exit(const VcpkgCmdArguments& args,