Add $FZF_DEFAULT_OPTS_FILE (#3618)

For those who prefer to manage default options in a file.
If the file is not found, fzf will exit with an error.

We're not setting a default value for it because:

1. it's hard to find a default value that can be universally agreed upon
2. to avoid fzf having to check for the existence of the file even when it's not used

5 files changed, 50 insertions, 7 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 19594f4f..f2d9354c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,12 @@ CHANGELOG
     - You would wonder why fzf implements directory traversal anyway when it's a filter program following the Unix philosophy.
       But fzf has had [the traversal code for years][walker] to tackle the performance problem on Windows. And I decided to use the same approach on different platforms as well for the benefits listed above.
     - Built-in traversal is now done using the excellent [charlievieth/fastwalk][fastwalk] library, which easily outperforms its competitors and supports safely following symlinks.
+- Added `$FZF_DEFAULT_OPTS_FILE` to allow managing default options in a file
+    - See [#3618](https://github.com/junegunn/fzf/pull/3618)
+    - Option precedence from lower to higher
+        1. Options read from `$FZF_DEFAULT_OPTS_FILE`
+        1. Options from `$FZF_DEFAULT_OPTS`
+        1. Options from command-line arguments
 
 [find]: https://github.com/junegunn/fzf/blob/0.46.1/src/constants.go#L60-L64
 [walker]: https://github.com/junegunn/fzf/pull/1847
diff --git a/README.md b/README.md
index 4c9b01fd..e0b367b6 100644
--- a/README.md
+++ b/README.md
@@ -329,6 +329,10 @@ or `py`.
 - `FZF_DEFAULT_OPTS`
     - Default options
     - e.g. `export FZF_DEFAULT_OPTS="--layout=reverse --inline-info"`
+- `FZF_DEFAULT_OPTS_FILE`
+    - If you prefer to manage default options in a file, set this variable to
+      point to the location of the file
+    - e.g. `export FZF_DEFAULT_OPTS_FILE=~/.fzfrc`
 
 ### Options
 
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index c10f334e..76bfa648 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -865,7 +865,14 @@ with \fB$SHELL -c\fR if \fBSHELL\fR is set, otherwise with \fBsh -c\fR, so in
 this case make sure that the command is POSIX-compliant.
 .TP
 .B FZF_DEFAULT_OPTS
-Default options. e.g. \fBexport FZF_DEFAULT_OPTS="--extended --cycle"\fR
+Default options.
+.br
+e.g. \fBexport FZF_DEFAULT_OPTS="--layout=reverse --border --cycle"\fR
+.TP
+.B FZF_DEFAULT_OPTS_FILE
+The location of the file that contains the default options.
+.br
+e.g. \fBexport FZF_DEFAULT_OPTS_FILE=~/.fzfrc\fR
 .TP
 .B FZF_API_KEY
 Can be used to require an API key when using \fB--listen\fR option. If not set,
diff --git a/src/options.go b/src/options.go
index dcb70dcb..09787a44 100644
--- a/src/options.go
+++ b/src/options.go
@@ -126,8 +126,8 @@ const usage = `usage: fzf [options]
 
   Environment variables
     FZF_DEFAULT_COMMAND    Default command to use when input is tty
-    FZF_DEFAULT_OPTS       Default options
-                           (e.g. '--layout=reverse --inline-info')
+    FZF_DEFAULT_OPTS       Default options (e.g. '--layout=reverse --info=inline')
+    FZF_DEFAULT_OPTS_FILE  Location of the file to read default options from
     FZF_API_KEY            X-API-Key header for HTTP server (--listen)
 
 `
@@ -421,8 +421,10 @@ func help(code int) {
 	os.Exit(code)
 }
 
+var errorContext = ""
+
 func errorExit(msg string) {
-	os.Stderr.WriteString(msg + "\n")
+	os.Stderr.WriteString(errorContext + msg + "\n")
 	os.Exit(exitError)
 }
 
@@ -2167,13 +2169,36 @@ func ParseOptions() *Options {
 		}
 	}
 
-	// Options from Env var
-	words, _ := shellwords.Parse(os.Getenv("FZF_DEFAULT_OPTS"))
+	// 1. Options from $FZF_DEFAULT_OPTS_FILE
+	if path := os.Getenv("FZF_DEFAULT_OPTS_FILE"); path != "" {
+		bytes, err := os.ReadFile(path)
+		if err != nil {
+			errorContext = "$FZF_DEFAULT_OPTS_FILE: "
+			errorExit(err.Error())
+		}
+
+		words, parseErr := shellwords.Parse(string(bytes))
+		if parseErr != nil {
+			errorContext = path + ": "
+			errorExit(parseErr.Error())
+		}
+		if len(words) > 0 {
+			parseOptions(opts, words)
+		}
+	}
+
+	// 2. Options from $FZF_DEFAULT_OPTS string
+	words, parseErr := shellwords.Parse(os.Getenv("FZF_DEFAULT_OPTS"))
+	errorContext = "$FZF_DEFAULT_OPTS: "
+	if parseErr != nil {
+		errorExit(parseErr.Error())
+	}
 	if len(words) > 0 {
 		parseOptions(opts, words)
 	}
 
-	// Options from command-line arguments
+	// 3. Options from command-line arguments
+	errorContext = ""
 	parseOptions(opts, os.Args[1:])
 
 	postProcessOptions(opts)
diff --git a/test/test_go.rb b/test/test_go.rb
index ecc111db..599d5442 100755
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -2582,6 +2582,7 @@ class TestGoFZF < TestBase
   def test_change_preview_window_rotate
     tmux.send_keys "seq 100 | #{FZF} --preview-window left,border-none --preview 'echo hello' --bind '" \
       "a:change-preview-window(right|down|up|hidden|)'", :Enter
+    tmux.until { |lines| assert(lines.any? { _1.include?('100/100') }) }
     3.times do
       tmux.until { |lines| lines[0].start_with?('hello') }
       tmux.send_keys 'a'