From 662fd84edabb3f30e4f6d9df0dda43a89bc25298 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Mon, 10 Apr 2017 08:13:35 -0600
Subject: [PATCH] raco: fix command name selection by prefix

Repairs a problem with 409321c03b.

Merge to v6.9
---
 pkgs/racket-test-extra/tests/raco/prefix.rkt | 15 +++++++++++++++
 racket/collects/raco/raco.rkt                |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 pkgs/racket-test-extra/tests/raco/prefix.rkt

diff --git a/pkgs/racket-test-extra/tests/raco/prefix.rkt b/pkgs/racket-test-extra/tests/raco/prefix.rkt
new file mode 100644
index 0000000000..ed918299c5
--- /dev/null
+++ b/pkgs/racket-test-extra/tests/raco/prefix.rkt
@@ -0,0 +1,15 @@
+#lang racket/base
+(require compiler/find-exe
+         racket/system)
+
+;; Make sure that `raco` recognizes unambiguous command prefixes.
+;; This test assumes that "pk" will unambiguously refer to "pkg".
+
+(define o (open-output-bytes))
+(parameterize ([current-output-port o])
+  (system* (find-exe)
+           "-N" "raco"
+           "-l-" "raco"
+           "pk"))
+(unless (regexp-match? #rx"raco pkg install" (get-output-bytes o))
+  (error "expected output from `raco pkg`"))
diff --git a/racket/collects/raco/raco.rkt b/racket/collects/raco/raco.rkt
index 9bb08b102e..8fd684b299 100644
--- a/racket/collects/raco/raco.rkt
+++ b/racket/collects/raco/raco.rkt
@@ -52,7 +52,7 @@
        [tool (and (pair? cmdline)
                   (or (hash-ref tools (car cmdline) #f)
                       (and (= (hash-count prefix-tools) 1)
-                           (hash-ref tools (car cmdline) #f))))]
+                           (car (hash-values prefix-tools)))))]
        [ambiguous? (> (hash-count prefix-tools) 1)]
        [show-all?
         (cond