From 0d0ee473fa73096cc7601a9169de4e2ac39d7163 Mon Sep 17 00:00:00 2001
From: Fabian Homborg <FHomborg@gmail.com>
Date: Fri, 25 Sep 2020 16:44:02 +0200
Subject: [PATCH] Detect windows line endings when executing a file

Fixes #2783.
---
 src/postfork.cpp       | 15 +++++++++++----
 tests/checks/exec.fish | 10 ++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/postfork.cpp b/src/postfork.cpp
index 6bb5b20aa..bf4cf0f10 100644
--- a/src/postfork.cpp
+++ b/src/postfork.cpp
@@ -360,10 +360,17 @@ void safe_report_exec_error(int err, const char *actual_cmd, const char *const *
             const char *interpreter =
                 get_interpreter(actual_cmd, interpreter_buff, sizeof interpreter_buff);
             if (interpreter && 0 != access(interpreter, X_OK)) {
-                debug_safe(0,
-                           "The file '%s' specified the interpreter '%s', which is not an "
-                           "executable command.",
-                           actual_cmd, interpreter);
+                // Detect windows line endings and complain specifically about them.
+                auto len = strlen(interpreter);
+                if (len && interpreter[len - 1] == '\r') {
+                    debug_safe(0,
+                               "The file uses windows line endings (\\r\\n). Run dos2unix or similar to fix it.");
+                } else {
+                    debug_safe(0,
+                               "The file '%s' specified the interpreter '%s', which is not an "
+                               "executable command.",
+                               actual_cmd, interpreter);
+                }
             } else {
                 debug_safe(0, "The file '%s' does not exist or could not be executed.", actual_cmd);
             }
diff --git a/tests/checks/exec.fish b/tests/checks/exec.fish
index 067d0e07e..656156dce 100644
--- a/tests/checks/exec.fish
+++ b/tests/checks/exec.fish
@@ -9,5 +9,15 @@ not exec cat <nosuchfile
 #CHECKERR: open: No such file or directory
 echo "neg failed: $status"
 #CHECK: neg failed: 0
+
+set -l f (mktemp)
+echo "#!/bin/sh"\r\n"echo foo" > $f
+chmod +x $f
+$f
+#CHECKERR: Failed to execute process '{{.*}}'. Reason:
+#CHECKERR: The file uses windows line endings (\r\n). Run dos2unix or similar to fix it.
+
+# This needs to be last, because it actually runs exec.
 exec cat </dev/null
 echo "not reached"
+