Handle the change in export-ignore default behaviour as well

Author: edolstra

src/libfetchers/git.cc

@@ -790,27 +790,27 @@ struct GitInputScheme : InputScheme
         bool smudgeLfs = getLfsAttr(input);
         auto accessor = repo->getAccessor(rev, exportIgnore, "«" + input.to_string(true) + "»", smudgeLfs);
 
-        /* Backward compatibility hack for locks produced by Nix < 2.20 that depend on Git filters. Nix >= 2.20 doesn't
-         * apply Git filters, so we may get a NAR hash mismatch. If that happens, try again with filters enabled. */
+        /* Backward compatibility hack for locks produced by Nix < 2.20 that depend on Nix applying Git filters or
+         * `export-ignore`. Nix >= 2.20 doesn't do those, so we may get a NAR hash mismatch. If that happens, try again
+         * with filters and export-ignore enabled. */
         if (auto expectedNarHash = input.getNarHash()) {
             if (accessor->pathExists(CanonPath(".gitattributes"))) {
                 accessor->fingerprint = makeFingerprint(input, rev);
-                auto narHashNoFilters =
+                auto narHashNew =
                     fetchToStore2(settings, *store, {accessor}, FetchMode::DryRun, input.getName()).second;
-                if (expectedNarHash != narHashNoFilters) {
-                    auto accessor2 =
-                        repo->getAccessor(rev, exportIgnore, "«" + input.to_string(true) + "»", smudgeLfs, true);
-                    accessor2->fingerprint = makeFingerprint(input, rev) + ";f";
-                    auto narHashFilters =
+                if (expectedNarHash != narHashNew) {
+                    auto accessor2 = repo->getAccessor(rev, true, "«" + input.to_string(true) + "»", smudgeLfs, true);
+                    accessor2->fingerprint = makeFingerprint(input, rev) + ";e;f";
+                    auto narHashOld =
                         fetchToStore2(settings, *store, {accessor2}, FetchMode::DryRun, input.getName()).second;
-                    if (expectedNarHash == narHashFilters) {
+                    if (expectedNarHash == narHashOld) {
                         warn(
-                            "Git input '%s' specifies a NAR hash '%s' that is only correct if Git filters are applied.\n"
-                            "This is pre-Nix 2.20 behavior; in Nix 2.20 and later, Git filters are not applied.\n"
+                            "Git input '%s' specifies a NAR hash '%s' that was created by Nix < 2.20.\n"
+                            "Nix >= 2.20 does not apply Git filters and `export-ignore` by default, which changes the NAR hash.\n"
                             "Please update the NAR hash to '%s'.",
                             input.to_string(),
                             expectedNarHash->to_string(HashFormat::SRI, true),
-                            narHashNoFilters.to_string(HashFormat::SRI, true));
+                            narHashNew.to_string(HashFormat::SRI, true));
                         accessor = accessor2;
                     }
                 }

tests/functional/fetchGit.sh

@@ -318,23 +318,27 @@ git init "$eol"
 git -C "$eol" config user.email "foobar@example.com"
 git -C "$eol" config user.name "Foobar"
 printf "Hello\nWorld\n" > "$eol/crlf"
-git -C "$eol" add crlf
+printf "ignore me" > "$eol/ignored"
+git -C "$eol" add crlf ignored
 git -C "$eol" commit -a -m Initial
-printf "crlf text eol=crlf\n" > "$eol/.gitattributes"
+printf "crlf text eol=crlf\nignored export-ignore\n" > "$eol/.gitattributes"
 git -C "$eol" add .gitattributes
 git -C "$eol" commit -a -m 'Apply gitattributes'
 
 rev="$(git -C "$eol" rev-parse HEAD)"
 
 export _NIX_TEST_BARF_ON_UNCACHEABLE=1
 
+oldHash="sha256-OizkFa+lIZbi+DCfbH8AYzsJ+BRmW0u/a7KKuzXADEU="
+newHash="sha256-hKHmbBsoVwqPNkL0MXL0RAtbOCqK6tP4xpX2tKR6GPI="
+
 expectStderr 0 nix eval --expr \
-    "assert builtins.readFile \"\${builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"sha256-kxXTCbD8wCYT9qNDKzl9bNKO8++pKY2QwAhqSqENP5k=\"; }}/crlf\" == \"Hello\r\nWorld\r\n\"; true" \
-    | grepQuiet "Please update the NAR hash to 'sha256-LDLvcwdcwCxnuPTxSQ6gLAyopB20lD0bOQoQB3i2hsA='"
+    "let tree = builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"$oldHash\"; }; in assert builtins.readFile \"\${tree}/crlf\" == \"Hello\r\nWorld\r\n\"; assert !builtins.pathExists \"\${tree}/ignored\"; true" \
+    | grepQuiet "Please update the NAR hash to '$newHash'"
 
 nix eval --expr \
-    "assert builtins.readFile \"\${builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"sha256-LDLvcwdcwCxnuPTxSQ6gLAyopB20lD0bOQoQB3i2hsA=\"; }}/crlf\" == \"Hello\nWorld\n\"; true"
+    "let tree = builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"$newHash\"; }; in assert builtins.readFile \"\${tree}/crlf\" == \"Hello\nWorld\n\"; assert builtins.pathExists \"\${tree}/ignored\"; true"
 
 expectStderr 102 nix eval --expr \
-    "assert builtins.readFile \"\${builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"sha256-DLDvcwdcwCxnuPTxSQ6gLAyopB20lD0bOQoQB3i2hsA=\"; }}/crlf\" == \"Hello\nWorld\n\"; true" \
+    "builtins.fetchTree { type = \"git\"; url = \"file://$eol\"; rev = \"$rev\"; narHash = \"sha256-DLDvcwdcwCxnuPTxSQ6gLAyopB20lD0bOQoQB3i2hsA=\"; }" \
     | grepQuiet "NAR hash mismatch"