51193: Discuss ERR_EXIT changes

ChangeLog

@@ -1,3 +1,7 @@
+2022-12-13  Bart Schaefer  <schaefer@zsh.org>
+
+	* Philippe Altherr: 51193: NEWS, README: Discuss ERR_EXIT changes
+
 2022-12-12  Peter Stephenson  <p.stephenson@samsung.com>
 
 	* 51134: Doc/Zsh/options.yo: document interactions between

NEWS

@@ -4,6 +4,14 @@ CHANGES FROM PREVIOUS VERSIONS OF ZSH
 
 Note also the list of incompatibilities in the README file.
 
+Changes since 5.9
+-----------------
+
+The ERR_EXIT and ERR_RETURN options were refined to be more self-
+consistent and better aligned with the POSIX-2017 specification of
+`set -e`. For details on what exactly changed, see the list of
+incompatibilities in the README file.
+
 Changes since 5.8.1
 -------------------
 

README

@@ -31,8 +31,56 @@ Zsh is a shell with lots of features.  For a list of some of these, see the
 file FEATURES, and for the latest changes see NEWS.  For more
 details, see the documentation.
 
-Incompatibilities since 5.8.1
------------------------------
+Incompatibilities since 5.9
+---------------------------
+
+The ERR_EXIT and ERR_RETURN options were refined to be more self-
+consistent and better aligned with the POSIX-2017 specification of
+`set -e`:
+
+  - Function calls or anonymous functions prefixed with `!` now never
+    trigger exit or return. Negated function calls or anonymous
+    functions used to trigger exit or return if ERR_EXIT or ERR_RETURN
+    was set and the function call or anonymous function returned a
+    zero exit status. Example:
+
+      setopt ERR_EXIT
+      f() { true }
+      ! f
+      echo "This is printed only since 5.10."
+
+  - The `always` command now ignores ERR_EXIT and ERR_RETURN, as other
+    complex commands do, if its exit status comes from a command
+    executed while the option is ignored. Example:
+
+      setopt ERR_EXIT
+      { false && true } always { echo "This was and still is printed." }
+      echo "This is printed only since 5.10."
+
+  - Function calls, anonymous functions, and the `eval`, `.`, and
+    `source` builtins now never ignore ERR_EXIT and ERR_RETURN on
+    their own. These commands used to ignore ERR_EXIT and ERR_RETURN
+    if their result came from a complex command (if, for, ...) whose
+    result came from a command executed while the option is
+    ignored. Example:
+
+      setopt ERR_EXIT
+      f() { if true; then false && true; fi }
+      f
+      echo "This is printed only prior to 5.10."
+
+  - The `&&` and `||` operators now always ignore ERR_RETURN in their
+    left operand. Until this version, the operators failed to ignored
+    ERR_RETURN in their left operand if they were executed as part of
+    a function call or an anonymous function that was itself executed
+    in a context where ERR_RETURN is ignored. Example:
+
+      setopt ERR_RETURN
+      f() { { false; echo "This is printed only since 5.10." } || true }
+      if f; then true; fi
+
+Incompatibilities between 5.8.1 and 5.9
+---------------------------------------
 
 compinit: A "y" response to the "Ignore ... and continue?" prompt removes
 insecure elements from the set of completion functions, where previously