Fix for #elif evaluation issue (#3038)

* A more way robust way to handle resource consumption might use multiple `kind`s on GLSL emit.

* Improve method naming and some comments.

* Small consistency fix.

* Fix issue with #elif evaluation.

* Add a test.

1 files changed, 25 insertions, 16 deletions

diff --git a/source/slang/slang-preprocessor.cpp b/source/slang/slang-preprocessor.cpp
index 6e7ae7cfb..4cc9bd113 100644
--- a/source/slang/slang-preprocessor.cpp
+++ b/source/slang/slang-preprocessor.cpp
@@ -86,7 +86,7 @@ struct Conditional
             /// The preprocessor should not skip tokens, and should not bother evaluating subsequent branch conditions.
         During,
 
-            /// Indicates that this conditional has laready seen the branch with a `true` condition
+            /// Indicates that this conditional has already seen the branch with a `true` condition
             ///
             /// The preprocessor should skip tokens, and should not bother evaluating subsequent branch conditions.
         After,
@@ -963,7 +963,7 @@ private:
     InputFile* m_parent = nullptr;
 
         /// The inner-most preprocessor conditional active for this file.
-    Conditional*        m_conditional = nullptr;
+    Conditional* m_conditional = nullptr;
 
         /// The lexer input stream that unexpanded tokens will be read from
     LexerInputStream* m_lexerStream;
@@ -2860,7 +2860,6 @@ static void HandleElifDirective(PreprocessorDirectiveContext* context)
     //
     // This is the behavior expected by at least one input program.
     // We will eventually want to be pedantic about this.
-    // even if t
     switch(PeekRawTokenType(context))
     {
     case TokenType::EndOfFile:
@@ -2870,8 +2869,6 @@ static void HandleElifDirective(PreprocessorDirectiveContext* context)
         return;
     }
 
-    PreprocessorExpressionValue value = _parseAndEvaluateExpression(context);
-
     // if we aren't inside a conditional, then error
     Conditional* conditional = inputFile->getInnerMostConditional();
     if (!conditional)
@@ -2890,17 +2887,29 @@ static void HandleElifDirective(PreprocessorDirectiveContext* context)
 
     switch (conditional->state)
     {
-    case Conditional::State::Before:
-        if(value)
-            conditional->state = Conditional::State::During;
-        break;
-
-    case Conditional::State::During:
-        conditional->state = Conditional::State::After;
-        break;
-
-    default:
-        break;
+        case Conditional::State::Before:
+        {
+            // Only evaluate the expression if we are in the before state.
+            const PreprocessorExpressionValue value = _parseAndEvaluateExpression(context);
+            if (value)
+            {
+                conditional->state = Conditional::State::During;
+            }
+            break;    
+        }
+        case Conditional::State::During:
+        {
+            // Consume to end of line, ignoring expression 
+            SkipToEndOfLine(context);
+            conditional->state = Conditional::State::After;
+            break;
+        }
+        default:
+        {
+            // Consume to end of line, ignoring expression
+            SkipToEndOfLine(context);
+            break;
+        }
     }
 
     updateLexerFlagsForConditionals(inputFile);