feat: warn when --full-path --glob pattern lacks path anchor (fixes #1650)

src/error.rs

@@ -1,3 +1,7 @@
 pub fn print_error(msg: impl Into<String>) {
     eprintln!("[fd error]: {}", msg.into());
 }
+
+pub fn print_warning(msg: impl Into<String>) {
+    eprintln!("[fd warning]: {}", msg.into());
+}

src/main.rs

@@ -26,6 +26,7 @@ use regex::bytes::{Regex, RegexBuilder, RegexSetBuilder};
 
 use crate::cli::{ColorWhen, HyperlinkWhen, Opts};
 use crate::config::Config;
+use crate::error::print_warning;
 use crate::exec::CommandSet;
 use crate::exit_codes::ExitCode;
 use crate::filetypes::FileTypes;
@@ -86,6 +87,7 @@ fn run() -> Result<ExitCode> {
     }
 
     ensure_search_pattern_is_not_a_path(&opts)?;
+    warn_if_full_path_glob_missing_leading_anchor(&opts);
     let pattern = &opts.pattern;
     let exprs = &opts.exprs;
     let empty = Vec::new();
@@ -201,6 +203,24 @@ fn ensure_search_pattern_is_not_a_path(opts: &Opts) -> Result<()> {
     }
 }
 
+/// With `--glob` and `--full-path`, patterns match the entire absolute path (from `/`).
+/// Warn when the pattern does not start with `/` or `*`, which often means no matches (#1650).
+fn warn_if_full_path_glob_missing_leading_anchor(opts: &Opts) {
+    if !opts.glob || !opts.full_path || opts.pattern.is_empty() {
+        return;
+    }
+    let Some(first) = opts.pattern.chars().next() else {
+        return;
+    };
+    if first == '/' || first == '*' {
+        return;
+    }
+    print_warning(
+        "With --glob and --full-path, the pattern matches the whole absolute path and \
+         usually should start with '/' or '**/' (for example: '**/foo.txt').",
+    );
+}
+
 fn build_pattern_regex(pattern: &str, opts: &Opts) -> Result<String> {
     Ok(if opts.glob && !pattern.is_empty() {
         let glob = GlobBuilder::new(pattern).literal_separator(true).build()?;

tests/tests.rs

@@ -590,6 +590,21 @@ fn test_full_path_glob_searches() {
     );
 }
 
+#[cfg(not(windows))]
+#[test]
+fn test_warn_when_full_path_glob_missing_leading_anchor() {
+    let te = TestEnv::new(DEFAULT_DIRS, DEFAULT_FILES);
+
+    te.assert_output(&["--glob", "--full-path", "foo.txt"], "");
+
+    let output = te.assert_success_and_get_output(".", &["--glob", "--full-path", "foo.txt"]);
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("[fd warning]:") && stderr.contains("**/foo.txt"),
+        "expected full-path glob anchor warning, got: {stderr}"
+    );
+}
+
 #[test]
 fn test_smart_case_glob_searches() {
     let te = TestEnv::new(DEFAULT_DIRS, DEFAULT_FILES);