git am应用补丁失败，为何patch命令可成功？如何排查原因？

Great question—this is a super common gotcha when working with git's patch tools vs. the standard patch command. Let's break down the root causes and why the two tools behave differently:

Why git am Rejected Your Patch #

First, let's cover why git am threw that "patch does not apply" error:

• Strict Context Matching: git am uses git's internal patch logic, which is pickier about matching the surrounding lines (context) of your changes. If the file product_cost_incl_bom/models/product_product.py has had even tiny edits near line 38 (like whitespace tweaks, a nearby line being modified, or code reformatting) since you created the patch, git am can't find an exact context match and bails out.
• Git-Specific Metadata Checks: Patches made with git format-patch include extra commit metadata (author info, timestamps, commit message headers). If you modified the patch file after generating it (even accidentally altering those metadata lines), git am might reject it because it expects a strict format.
• Default Whitespace Sensitivity: Out of the box, git am is way more sensitive to whitespace inconsistencies than patch. For example, if your patch has trailing spaces or indentation that doesn't match the current file, git am will flag it as a failure immediately.

Why patch Applied It Successfully #

The standard patch tool is a general-purpose diff applier built to be forgiving, which is why it worked where git am didn't:

• Heuristic Context Matching: Instead of requiring an exact context match, patch uses a smart heuristic to find the closest possible match for the lines around your changes. It can tolerate small differences in surrounding code that git am would reject outright.
• Ignores Git Metadata: patch doesn't care about the extra commit headers added by git format-patch—it only parses the actual diff content. So even if the patch's metadata was messed up, patch just skips that and applies the code changes.
• Relaxed Whitespace Rules: Unless you pass specific flags to make it strict, patch ignores minor whitespace differences (like trailing spaces or inconsistent indentation) that would trip up git am.

Fixing git am for This Patch #

If you want to stick with git am (which preserves commit metadata, a big plus), try these fixes:

• Run git am --whitespace=fix to let git automatically correct whitespace mismatches that might be causing the failure.
• Use git am -3 to enable three-way merging. This tells git to use its merge tools to resolve conflicts between the patch and your current file state, instead of just rejecting the patch.
• If the context is the issue, manually edit the patch file to update the surrounding lines (the ones between the @@ markers) to match the current state of product_product.py, then run git am again.

内容的提问来源于stack exchange，提问作者Loïc Faure-Lacroix