[PATCH v4] convert: avoid high memory footprint

From: D Harithamma <harithamma.d@ibm.com>

When Git adds a file requiring encoding conversion and tracing of encoding conversion is not requested via the GIT_TRACE_WORKING_TREE_ENCODING environment variable, the `trace_encoding()` function still allocates & prepares "human readable" copies of the file contents before and after conversion to show in the trace. This results in a high memory footprint and increased runtime without providing any user-visible benefit.

This fix introduces an early exit from the `trace_encoding()` function when tracing is not requested, preventing unnecessary memory allocation and processing.

Signed-off-by: Harithamma D <harithamma.d@ibm.com>
---
    Fix to avoid high memory footprint
    
    This fix avoids high memory footprint when adding files that require
    conversion
    
    Git has a trace_encoding routine that prints trace output when
    GIT_TRACE_WORKING_TREE_ENCODING=1 is set. This environment variable is
    used to debug the encoding contents. When a 40MB file is added, it
    requests close to 1.8GB of storage from xrealloc which can lead to out
    of memory errors. However, the check for GIT_TRACE_WORKING_TREE_ENCODING
    is done after the string is allocated. This resolves high memory
    footprints even when GIT_TRACE_WORKING_TREE_ENCODING is not active. This
    fix adds an early exit to avoid the unnecessary memory allocation.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1744%2FHarithaIBM%2FmemFootprintFix-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1744/HarithaIBM/memFootprintFix-v4
Pull-Request: https://github.com/git/git/pull/1744

Range-diff vs v3:

 1:  d864de64380 ! 1:  50758a4fb94 Fix to avoid high memory footprint
     @@ Metadata
      Author: D Harithamma <harithamma.d@ibm.com>
      
       ## Commit message ##
     -    Fix to avoid high memory footprint
     +    convert: avoid high memory footprint
      
          When Git adds a file requiring encoding conversion and tracing of encoding
          conversion is not requested via the GIT_TRACE_WORKING_TREE_ENCODING

 convert.c | 3 +++
 1 file changed, 3 insertions(+)