cli: jj absorb warns when fileset doesn't exist

Author: whereistejas

CHANGELOG.md

@@ -85,6 +85,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 * Revsets now support logical operators in string patterns.
 
+* All `jj` commands show a warning when the provided `fileset` expression 
+  doesn't match any files.
+
 ### Fixed bugs
 
 * `jj metaedit --author-timestamp` twice with the same value no longer

cli/src/commands/absorb.rs

@@ -22,6 +22,7 @@ use tracing::instrument;
 
 use crate::cli_util::CommandHelper;
 use crate::cli_util::RevisionArg;
+use crate::cli_util::print_unmatched_explicit_paths;
 use crate::cli_util::print_updated_commits;
 use crate::command_error::CommandError;
 use crate::complete;
@@ -81,14 +82,20 @@ pub(crate) fn cmd_absorb(
         .parse_union_revsets(ui, &args.into)?
         .resolve()?;
 
-    let matcher = workspace_command
-        .parse_file_patterns(ui, &args.paths)?
-        .to_matcher();
+    let fileset_expression = workspace_command.parse_file_patterns(ui, &args.paths)?;
+    let matcher = fileset_expression.to_matcher();
 
     let repo = workspace_command.repo().as_ref();
-    let source = AbsorbSource::from_commit(repo, source_commit)?;
+    let source = AbsorbSource::from_commit(repo, source_commit.clone())?;
     let selected_trees = split_hunks_to_trees(repo, &source, &destinations, &matcher).block_on()?;
 
+    print_unmatched_explicit_paths(
+        ui,
+        &workspace_command,
+        &fileset_expression,
+        [&source_commit.tree()?],
+    )?;
+
     let path_converter = workspace_command.path_converter();
     for (path, reason) in selected_trees.skipped_paths {
         let ui_path = path_converter.format_file_path(&path);

cli/tests/test_absorb_command.rs

@@ -810,9 +810,10 @@ fn test_absorb_paths() {
     work_dir.write_file("file1", "1A\n");
     work_dir.write_file("file2", "1A\n");
 
-    let output = work_dir.run_jj(["absorb", "unknown"]);
+    let output = work_dir.run_jj(["absorb", "nonexistent"]);
     insta::assert_snapshot!(output, @r"
     ------- stderr -------
+    Warning: No matching entries for paths: nonexistent
     Nothing changed.
     [EOF]
     ");