Allow Formatter to be invalid.

Rather than CHECKing, we can return a Formatter
which is invalid.

Bug: 65738957
Test: makefiles/host tests
Change-Id: Ic9a7a0ffdf6d0c7d7b84f22e042b372ab9a45d41

2 files changed, 20 insertions, 3 deletions

diff --git a/utils/Formatter.cpp b/utils/Formatter.cpp
index 83caf8d1..7fa0be59 100644
--- a/utils/Formatter.cpp
+++ b/utils/Formatter.cpp
@@ -18,8 +18,12 @@
 
 #include <assert.h>
 
+#include <android-base/logging.h>
+
 namespace android {
 
+Formatter::Formatter() : mFile(NULL /* invalid */), mIndentDepth(0), mAtStartOfLine(true) {}
+
 Formatter::Formatter(FILE *file)
     : mFile(file == NULL ? stdout : file),
       mIndentDepth(0),
@@ -184,7 +188,13 @@ void Formatter::setNamespace(const std::string &space) {
     mSpace = space;
 }
 
+bool Formatter::isValid() const {
+    return mFile != nullptr;
+}
+
 void Formatter::output(const std::string &text) const {
+    CHECK(isValid());
+
     fprintf(mFile, "%s", text.c_str());
 }
 
diff --git a/utils/include/hidl-util/Formatter.h b/utils/include/hidl-util/Formatter.h
index 2f7c02d1..9e6d728f 100644
--- a/utils/include/hidl-util/Formatter.h
+++ b/utils/include/hidl-util/Formatter.h
@@ -30,9 +30,11 @@ namespace android {
 // The other is with chain calls and lambda functions
 //     out.sIf("good", [&] { out("blah").endl()("blah").endl(); }).endl();
 struct Formatter {
+    static Formatter invalid() { return Formatter(); }
 
     // Assumes ownership of file. Directed to stdout if file == NULL.
-    Formatter(FILE *file = NULL);
+    Formatter(FILE* file);
+    Formatter(Formatter&&) = default;
     ~Formatter();
 
     void indent(size_t level = 1);
@@ -138,8 +140,13 @@ struct Formatter {
     // Remove the line prefix.
     void unsetLinePrefix();
 
-private:
-    FILE *mFile;
+    bool isValid() const;
+
+   private:
+    // Creates an invalid formatter object.
+    Formatter();
+
+    FILE* mFile;  // invalid if nullptr
     size_t mIndentDepth;
     bool mAtStartOfLine;