Apply source map section columns only to their first line

CHANGELOG.md

@@ -1,5 +1,7 @@
 **Master**
 
+- Apply source map section columns only to their first line. [Oskar Eichler](https://github.com/OskarEichler)
+
 Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprockets/blob/master/UPGRADING.md
 
 # 4.4.1

README.md

@@ -714,3 +714,5 @@ Please see the [CHANGELOG](https://github.com/rails/sprockets/tree/master/CHANGE
 
 ## License
 Sprockets is released under the [MIT License](MIT-LICENSE).
+
+Index source map column offsets apply only to the first generated line of each section, while line offsets apply to all lines.

lib/sprockets/source_map_utils.rb

@@ -196,8 +196,8 @@ def decode_source_map(map)
       if map["sections"]
         map["sections"].each do |s|
           mappings += decode_source_map(s["map"])[:mappings].each do |m|
+            m[:generated][1] += s["offset"]["column"] if m[:generated][0] == 1
             m[:generated][0] += s["offset"]["line"]
-            m[:generated][1] += s["offset"]["column"]
           end
           sources |= s["map"]["sources"]
           names   |= s["map"]["names"]