From 411b24361e31503171b2940ebd44dc436550a716 Mon Sep 17 00:00:00 2001
From: Tim Foley <tfoley@nvidia.com>
Date: Mon, 19 Jun 2017 13:20:53 -0700
Subject: Don't emit redundant `#line` directives

If the line number for the next token is within a small range, then go ahead and output newlines to get caught up, rather than emit a `#line` directive. This saves a small amount of clutter, and in the particular case where the number of lines is 1, it stops our current behavior of putting a directive on each line.
---
 source/slang/emit.cpp | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

(limited to 'source')

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index ef5df830f..21ae498b6 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -1424,6 +1424,9 @@ static void emitLineDirective(
                 emitRawText(context, charBuffer);
                 break;
 
+            // The incoming file path might use `/` and/or `\\` as
+            // a directory separator. We want to canonicalize this.
+            //
             // TODO: should probably canonicalize paths to not use backslash somewhere else
             // in the compilation pipeline...
             case '\\':
@@ -1463,7 +1466,26 @@ static void advanceToSourceLocation(
         || sourceLocation.Line != context->loc.Line
         || sourceLocation.Col < context->loc.Col)
     {
-        emitLineDirectiveAndUpdateSourceLocation(context, sourceLocation);
+        // Special case: if we are in the same file, and within a small number
+        // of lines of the target location, then go ahead and output newlines
+        // to get us caught up.
+        enum { kSmallLineCount = 3 };
+        auto lineDiff = sourceLocation.Line - context->loc.Line;
+        if(sourceLocation.FileName == context->loc.FileName
+            && sourceLocation.Line > context->loc.Line
+            && lineDiff <= kSmallLineCount)
+        {
+            for(int ii = 0; ii < lineDiff; ++ii )
+            {
+                Emit(context, "\n");
+            }
+            assert(sourceLocation.Line == context->loc.Line);
+        }
+        else
+        {
+            // Go ahead and output a `#line` directive to get us caught up
+            emitLineDirectiveAndUpdateSourceLocation(context, sourceLocation);
+        }
     }
 
     // Now indent up to the appropriate column, so that error messages
-- 
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