From 268896444bed7b958add74b2e1e86ff802c5f5cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 16 Aug 2019 18:41:55 +0200
Subject: [PATCH] derivations: Delete duplicate inputs when computing
 derivation hash.

Fixes <https://bugs.gnu.org/36777>.
Reported by Carl Dong <contact@carldong.me>.

* guix/derivations.scm (derivation/masked-inputs): Call
'delete-duplicates' on INPUTS.
* tests/derivations.scm ("derivation with duplicate fixed-output inputs"):
New test.
---
 guix/derivations.scm  |  2 +-
 tests/derivations.scm | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/guix/derivations.scm b/guix/derivations.scm
index 92d50503ce..b3928920e2 100644
--- a/guix/derivations.scm
+++ b/guix/derivations.scm
@@ -685,7 +685,7 @@ name of each input with that input's hash."
                              (make-derivation-input hash sub-drvs))))
                         inputs)))
        (make-derivation outputs
-                        (sort inputs
+                        (sort (delete-duplicates inputs)
                               (lambda (drv1 drv2)
                                 (string<? (derivation-input-derivation drv1)
                                           (derivation-input-derivation drv2))))
diff --git a/tests/derivations.scm b/tests/derivations.scm
index 368012d2b2..db73d19b3a 100644
--- a/tests/derivations.scm
+++ b/tests/derivations.scm
@@ -410,6 +410,38 @@
          (equal? (derivation->output-path final1)
                  (derivation->output-path final2)))))
 
+(test-assert "derivation with duplicate fixed-output inputs"
+  ;; Here we create a derivation that has two inputs, both of which are
+  ;; fixed-output leading to the same result.  This test ensures the hash of
+  ;; that derivation is correctly computed, namely that duplicate inputs are
+  ;; coalesced.  See <https://bugs.gnu.org/36777>.
+  (let* ((builder1   (add-text-to-store %store "fixed-builder1.sh"
+                                        "echo -n hello > $out" '()))
+         (builder2   (add-text-to-store %store "fixed-builder2.sh"
+                                        "echo hey; echo -n hello > $out" '()))
+         (hash       (sha256 (string->utf8 "hello")))
+         (fixed1     (derivation %store "fixed"
+                                 %bash `(,builder1)
+                                 #:hash hash #:hash-algo 'sha256))
+         (fixed2     (derivation %store "fixed"
+                                 %bash `(,builder2)
+                                 #:hash hash #:hash-algo 'sha256))
+         (builder3   (add-text-to-store %store "builder.sh"
+                                        "echo fake builder"))
+         (final      (derivation %store "final"
+                                 %bash `(,builder3)
+                                 #:sources (list %bash builder3)
+                                 #:inputs (list (derivation-input fixed1)
+                                                (derivation-input fixed2)))))
+    (and (derivation? final)
+         (match (derivation-inputs final)
+           (((= derivation-input-derivation one)
+             (= derivation-input-derivation two))
+            (and (not (string=? (derivation-file-name one)
+                                (derivation-file-name two)))
+                 (string=? (derivation->output-path one)
+                           (derivation->output-path two))))))))
+
 (test-assert "multiple-output derivation"
   (let* ((builder    (add-text-to-store %store "my-fixed-builder.sh"
                                         "echo one > $out ; echo two > $second"