pathmatcher: provide a hint when users use -R with a cwd-relative path

Summary:
A common mistake is to use -R, but specify a file relative to the repo
instead of cwd.  Detect that case, and provide a hint to the user.

Reviewed By: muirdm

Differential Revision: D69250238

fbshipit-source-id: 84195a55a4e5986d809d3c3055aca64e1d18ab0c

eden/scm/lib/pathmatcher/src/error.rs

@@ -7,15 +7,30 @@
 
 #[derive(Debug, thiserror::Error)]
 pub enum Error {
-    #[error("unsuppported pattern kind {0}")]
     UnsupportedPatternKind(String),
-
-    #[error("{0} not under root '{1}'")]
-    PathOutsideRoot(String, String),
-
-    #[error("non-utf8 path '{0}' when building pattern")]
+    PathOutsideRoot(String, String, bool),
     NonUtf8(String),
-
-    #[error("listfile:- may only be used once as a direct CLI argument")]
     StdinUnavailable,
 }
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Error::UnsupportedPatternKind(s) => write!(f, "unsupported pattern kind {}", s),
+            Error::PathOutsideRoot(path, root, show_hint) => {
+                let message = format!("cwd relative path '{}' is not under root '{}'", path, root);
+                if *show_hint {
+                    let hint_message = "consider using --cwd to change working directory";
+                    write!(f, "{}\n(hint: {})", message, hint_message)
+                } else {
+                    write!(f, "{}", message)
+                }
+            }
+            Error::NonUtf8(s) => write!(f, "non-utf8 path '{}' when building pattern", s),
+            Error::StdinUnavailable => write!(
+                f,
+                "listfile:- may only be used once as a direct CLI argument"
+            ),
+        }
+    }
+}

eden/scm/lib/pathmatcher/src/pattern.rs

@@ -226,9 +226,11 @@ where
                         .into_string()
                         .map_err(|s| Error::NonUtf8(s.to_string_lossy().to_string()))?,
                     None => {
+                        let show_hint = !cwd.starts_with(root);
                         return Err(Error::PathOutsideRoot(
                             pat.to_string(),
                             root.to_string_lossy().to_string(),
+                            show_hint,
                         )
                         .into());
                     }

eden/scm/tests/test-alias.t

@@ -148,7 +148,8 @@ no closing quotation
 "--" in alias definition should be preserved
 
   $ hg --config alias.dash='cat --' -R alias dash -r0
-  abort: -r0 not under root '$TESTTMP/alias'
+  abort: cwd relative path '-r0' is not under root '$TESTTMP/alias'
+  (hint: consider using --cwd to change working directory)
   [255]
 
 invalid options

eden/scm/tests/test-parents.t

@@ -75,7 +75,8 @@ hg parents c, single revision
 
 
   $ hg parents -r 'max(desc(b))' ../a
-  abort: ../a not under root '$TESTTMP/repo'
+  abort: cwd relative path '../a' is not under root '$TESTTMP/repo'
+  (hint: consider using --cwd to change working directory)
   [255]
 
 

eden/scm/tests/test-walk.t

@@ -275,10 +275,12 @@
   f  mammals/Procyonidae/raccoon     mammals/Procyonidae/raccoon
   f  mammals/skunk                   mammals/skunk
   $ hg debugwalk ..
-  abort: .. not under root '$TESTTMP/t'
+  abort: cwd relative path '..' is not under root '$TESTTMP/t'
+  (hint: consider using --cwd to change working directory)
   [255]
   $ hg debugwalk beans/../..
-  abort: beans/../.. not under root '$TESTTMP/t'
+  abort: cwd relative path 'beans/../..' is not under root '$TESTTMP/t'
+  (hint: consider using --cwd to change working directory)
   [255]
   $ hg debugwalk .hg
   abort: path contains illegal component: .hg
@@ -306,7 +308,8 @@ Test absolute paths:
   f  beans/pinto     beans/pinto
   f  beans/turtle    beans/turtle
   $ hg debugwalk `pwd`/..
-  abort: $TESTTMP/t/.. not under root '$TESTTMP/t'
+  abort: cwd relative path '$TESTTMP/t/..' is not under root '$TESTTMP/t'
+  (hint: consider using --cwd to change working directory)
   [255]
 
 Test patterns: