Piping `hledger rewrite --diff` to `patch` fails

[MatejaMaric]

Output of hledger setup:

Checking your hledger setup..
Legend: good, neutral, unknown, warning

hledger
* is a released version ?                  yes  hledger 1.51.2, mac-aarch64
* is up to date ?                          yes  1.51.2 installed, latest is 1.51.2
* is a native binary for this machine ?    yes  aarch64
* is installed in PATH (this version) ?    yes  /opt/homebrew/bin/hledger
* has a system text encoding configured ?  yes  UTF-8, data files must use this encoding
* has a user config file ?                  no
* has a local config file ?                 no

terminal
* the NO_COLOR variable is defined ?        no
* --color is configured by config file ?    no
* hledger will use color by default ?      yes
* the PAGER variable is defined ?           no
* --pager is configured by config file ?    no
* hledger will use a pager when needed ?   yes  /usr/bin/less
* the LESS variable is defined ?           yes
* the HLEDGER_LESS variable is defined ?    no
* adjusting LESS variable for color etc. ? yes
* tables will use box-drawing chars ?       no  you can use --pretty to enable them

journal
* the LEDGER_FILE variable is defined ?    yes  /Users/mateja/Documents/finance/potrosnja.hledger
* a default journal file is readable ?     yes  /Users/mateja/Documents/finance/potrosnja.hledger
* it includes additional files ?           yes  6 files
* all commodities are declared ?           yes  5 commodities
* all accounts are declared ?              yes  84 accounts
* all accounts have types ?                 no  10 accounts without types
* accounts of all types exist ?            yes  ALERXCV accounts detected
* commodities/accounts are being checked ?  no  you can use -s to check them
* balance assertions are being checked ?   yes  you can use -I to ignore them

Operating system I'm running:

  System Version:	macOS 26.2 (25C56)
  Kernel Version:	Darwin 25.2.0

Link to the most relevant doc that I found: https://hledger.org/1.51/hledger.html#diff-output-format

Reproducible example:

sample.journal

= expenses:groceries date:2026-01-01..
    assets:funds:budget:month:food      *-1
    liabilities:funds                    *1

2026-01-01 Supermarket
    expenses:groceries     100 USD
    assets:bank           -100 USD

2026-01-02 Something
    expenses:other         100 USD
    assets:bank           -100 USD

2026-01-03 Something
    expenses:other         100 USD
    assets:bank           -100 USD

2026-01-04 Supermarket
    expenses:groceries     100 USD
    assets:bank           -100 USD

2026-01-05 Something
    expenses:other         100 USD
    assets:bank           -100 USD

When I run hledger rewrite --diff -f sample.journal | patch I get the following error:

patching file sample.journal
2 out of 2 hunks failed--saving rejects to sample.journal.rej

Content of sample.journal.rej:

@@ -5,3 +5,5 @@
 2026-01-01 Supermarket
-    expenses:groceries     100 USD
-    assets:bank           -100 USD
+    expenses:groceries                     100 USD
+    assets:funds:budget:month:food        -100 USD
+    liabilities:funds                      100 USD
+    assets:bank                           -100 USD
@@ -17,3 +19,5 @@
 2026-01-04 Supermarket
-    expenses:groceries     100 USD
-    assets:bank           -100 USD
+    expenses:groceries                     100 USD
+    assets:funds:budget:month:food        -100 USD
+    liabilities:funds                      100 USD
+    assets:bank                           -100 USD

[simonmichael]

Thanks for the report @MatejaMaric. Apparently the problem is that we are not showing enough trailing context so that patch can reliably apply our diffs. We use the Diff lib and newer versions of that have the ability to provide context; I think our code could be updated to use that (I made a quick attempt but failed).