DiagnosticStream can convert to a stored error code

Use this to shorten error return code in the assembler.

For example, change this:

   if (error = something()) {
      diagnostic() << " Bad integer literal " << value;
      return SPV_ERROR_INVALID_VALUE;
   }

to this:

   if (error = something())
      return diagnostic() << " Bad integer literal " << value;

Also shorten code due to the fact that binaryEncodeU32 and
binaryCodeU64 can't fail (short of failure to expand a std::vector).

1 files changed, 19 insertions, 8 deletions

diff --git a/source/diagnostic.h b/source/diagnostic.h
index 4e6d3789..27be491e 100644
--- a/source/diagnostic.h
+++ b/source/diagnostic.h
@@ -31,6 +31,7 @@
 
 #include <iostream>
 #include <sstream>
+#include <utility>
 
 class diagnostic_helper {
  public:
@@ -51,20 +52,26 @@ class diagnostic_helper {
   spv_diagnostic *pDiagnostic;
 };
 
-// On destruction of the diagnostic stream, a diagnostic message will be
-// written to pDiagnostic containing all of the data written to the stream.
+// A DiagnosticStream remembers the current position of the input and an error
+// code, and captures diagnostic messages via the left-shift operator.
+// Captured messages are emitted during the destructor.
 // TODO(awoloszyn): This is very similar to diagnostic_helper, and hides
 //                  the data more easily. Replace diagnostic_helper elsewhere
 //                  eventually.
 class DiagnosticStream {
  public:
-  DiagnosticStream(spv_position position, spv_diagnostic *pDiagnostic)
-      : position_(position), pDiagnostic_(pDiagnostic) {}
+  DiagnosticStream(spv_position position, spv_diagnostic *pDiagnostic,
+                   spv_result_t error)
+      : position_(position), pDiagnostic_(pDiagnostic), error_(error) {}
 
-  DiagnosticStream(DiagnosticStream &&other) : position_(other.position_) {
-    stream_.str(other.stream_.str());
-    other.stream_.str("");
-    pDiagnostic_ = other.pDiagnostic_;
+  DiagnosticStream(DiagnosticStream &&other)
+      : stream_(other.stream_.str()),
+        position_(other.position_),
+        pDiagnostic_(other.pDiagnostic_),
+        error_(other.error_) {
+    // The other object's destructor will emit the text in its stream_
+    // member if its pDiagnostic_ member is non-null.  Prevent that,
+    // since emitting that text is now the responsibility of *this.
     other.pDiagnostic_ = nullptr;
   }
 
@@ -77,10 +84,14 @@ class DiagnosticStream {
     return *this;
   }
 
+  // Conversion operator to spv_result, returning the error code.
+  operator spv_result_t() { return error_; }
+
  private:
   std::stringstream stream_;
   spv_position position_;
   spv_diagnostic *pDiagnostic_;
+  spv_result_t error_;
 };
 
 #define DIAGNOSTIC                                 \