Don't show acquire warning for "hidden" components

Commit d7c92411dc1f4c6be098d1425f9c1c075e0c2154 introduced a warning for
non-existent files from components not mentioned in Components to hint
users at a mispelling or the disappearance of a component.

The debian-installer subcomponent isn't actively advertised in the
Release file through, so if apt ends up in acquiring a file which
doesn't exist for this component (like Translation files) apt would
produce a warning:

W: Skipping acquire of configured file
'main/debian-installer/i18n/Translation-en' as repository
'http://deb.debian.org/debian buster InRelease' doesn't have the
component 'main/debian-installer' (component misspelt in sources.list?)

We prevent this in the future by checking if any file exists from this
component which results in the warning to be produced still for the
intended cases and silence it on the d-i case.

This could potentially cause the warning not to be produced in cases it
should be if some marginal file remains, but as this message is just a
hint and the setup a bit pathological lets ignore it for now.

There is also the possibility of having no file present as they would
all be 0-length files and being a "hidden" component, but that would be
easy to workaround from the repository side and isn't really actively used
at the moment in the wild.

Closes: #879591

3 files changed, 58 insertions, 10 deletions

diff --git a/apt-pkg/acquire-item.cc b/apt-pkg/acquire-item.cc
index a366b8981..0126b0f63 100644
--- a/apt-pkg/acquire-item.cc
+++ b/apt-pkg/acquire-item.cc
@@ -39,6 +39,7 @@
 #include <random>
 #include <sstream>
 #include <string>
+#include <unordered_set>
 #include <vector>
 #include <errno.h>
 #include <stddef.h>
@@ -1511,7 +1512,7 @@ void pkgAcqMetaClearSig::QueueIndexes(bool const verify)			/*{{{*/
    // at this point the real Items are loaded in the fetcher
    ExpectedAdditionalItems = 0;
 
-   std::set<std::string> targetsSeen;
+   std::unordered_set<std::string> targetsSeen, componentsSeen;
    bool const hasReleaseFile = TransactionManager->MetaIndexParser != NULL;
    bool hasHashes = true;
    auto IndexTargets = TransactionManager->MetaIndexParser->GetIndexTargets();
@@ -1535,6 +1536,18 @@ void pkgAcqMetaClearSig::QueueIndexes(bool const verify)			/*{{{*/
 	 range_start = range_end;
       } while (range_start != IndexTargets.end());
    }
+   /* Collect all components for which files exist to prevent apt from warning users
+      about "hidden" components for which not all files exist like main/debian-installer
+      and Translation files */
+   if (hasReleaseFile == true)
+      for (auto const &Target : IndexTargets)
+	 if (TransactionManager->MetaIndexParser->Exists(Target.MetaKey))
+	 {
+	    auto component = Target.Option(IndexTarget::COMPONENT);
+	    if (component.empty() == false)
+	       componentsSeen.emplace(std::move(component));
+	 }
+
    for (auto&& Target: IndexTargets)
    {
       // if we have seen a target which is created-by a target this one here is declared a
@@ -1566,7 +1579,9 @@ void pkgAcqMetaClearSig::QueueIndexes(bool const verify)			/*{{{*/
 	 if (TransactionManager->MetaIndexParser->Exists(Target.MetaKey) == false)
 	 {
 	    auto const component = Target.Option(IndexTarget::COMPONENT);
-	    if (component.empty() == false && TransactionManager->MetaIndexParser->HasSupportForComponent(component) == false)
+	    if (component.empty() == false &&
+		componentsSeen.find(component) == std::end(componentsSeen) &&
+		TransactionManager->MetaIndexParser->HasSupportForComponent(component) == false)
 	    {
 	       new CleanupItem(Owner, TransactionManager, Target);
 	       _error->Warning(_("Skipping acquire of configured file '%s' as repository '%s' doesn't have the component '%s' (component misspelt in sources.list?)"),
diff --git a/test/integration/framework b/test/integration/framework
index f7c68859f..cfd621105 100644
--- a/test/integration/framework
+++ b/test/integration/framework
@@ -909,10 +909,17 @@ insertpackage() {
  If you find such a package installed on your system,
  something went horribly wrong! They are autogenerated
  und used only by testcases and serve no other purpose…}"
+	local SECTION="${8:-other}"
+
+	if [ "$SECTION" = "${SECTION#*/}" ]; then
+		DISTSECTION="main"
+	else
+		DISTSECTION="${SECTION%/*}"
+	fi
 	local ARCHS=""
 	for RELEASE in $(printf '%s' "$RELEASES" | tr ',' '\n'); do
 		if [ "$RELEASE" = 'installed' ]; then
-			insertinstalledpackage "$2" "$3" "$4" "$5" "$6" "$7"
+			insertinstalledpackage "$2" "$3" "$4" "$5" "$6" "$7" "$8"
 			continue
 		fi
 		for arch in $(getarchitecturesfromcommalist "$ARCH"); do
@@ -922,17 +929,17 @@ insertpackage() {
 				ARCHS="$arch"
 			fi
 			for BUILDARCH in $ARCHS; do
-				local PPATH="aptarchive/dists/${RELEASE}/main/binary-${BUILDARCH}"
+				local PPATH="aptarchive/dists/${RELEASE}/${DISTSECTION}/binary-${BUILDARCH}"
 				mkdir -p "$PPATH"
 				{
 					echo "Package: $NAME
 Priority: $PRIORITY
-Section: other
+Section: $SECTION
 Installed-Size: 42
 Maintainer: Joe Sixpack <joe@example.org>"
 					test "$arch" = 'none' || echo "Architecture: $arch"
 					echo "Version: $VERSION
-Filename: pool/main/${NAME}/${NAME}_${VERSION}_${arch}.deb"
+Filename: pool/${DISTSECTION}/${NAME}/${NAME}_${VERSION}_${arch}.deb"
 					test -z "$DEPENDENCIES" || printf "%b\n" "$DEPENDENCIES"
 					echo "Description: $(printf '%s' "$DESCRIPTION" | head -n 1)"
 					echo "Description-md5: $(printf '%s' "$DESCRIPTION" | md5sum | cut -d' ' -f 1)"
@@ -941,12 +948,12 @@ Filename: pool/main/${NAME}/${NAME}_${VERSION}_${arch}.deb"
 				} >> "${PPATH}/Packages"
 			done
 		done
-		mkdir -p "aptarchive/dists/${RELEASE}/main/source" "aptarchive/dists/${RELEASE}/main/i18n"
-		touch "aptarchive/dists/${RELEASE}/main/source/Sources"
+		mkdir -p "aptarchive/dists/${RELEASE}/${DISTSECTION}/source" "aptarchive/dists/${RELEASE}/${DISTSECTION}/i18n"
+		touch "aptarchive/dists/${RELEASE}/${DISTSECTION}/source/Sources"
 		echo "Package: $NAME
 Description-md5: $(printf '%s' "$DESCRIPTION" | md5sum | cut -d' ' -f 1)
 Description-en: $DESCRIPTION
-" >> "aptarchive/dists/${RELEASE}/main/i18n/Translation-en"
+" >> "aptarchive/dists/${RELEASE}/${DISTSECTION}/i18n/Translation-en"
 	done
 }
 
@@ -991,6 +998,7 @@ insertinstalledpackage() {
  If you find such a package installed on your system,
  something went horribly wrong! They are autogenerated
  und used only by testcases and serve no other purpose…}"
+	local SECTION="${8:-other}"
 
 	local FILE='rootdir/var/lib/dpkg/status'
 	local INFO='rootdir/var/lib/dpkg/info'
@@ -998,7 +1006,7 @@ insertinstalledpackage() {
 		echo "Package: $NAME
 Status: $STATUS
 Priority: $PRIORITY
-Section: other
+Section: $SECTION
 Installed-Size: 42
 Maintainer: Joe Sixpack <joe@example.org>
 Version: $VERSION" >> "$FILE"
diff --git a/test/integration/test-bug-879591-dont-warn-for-hidden-but-good-components b/test/integration/test-bug-879591-dont-warn-for-hidden-but-good-components
new file mode 100755
index 000000000..6eb4e04a6
--- /dev/null
+++ b/test/integration/test-bug-879591-dont-warn-for-hidden-but-good-components
@@ -0,0 +1,25 @@
+#!/bin/sh
+set -e
+
+TESTDIR="$(readlink -f "$(dirname "$0")")"
+. "$TESTDIR/framework"
+setupenvironment
+configarchitecture 'amd64'
+
+insertpackage 'stable' 'foo' 'all' '1'
+insertpackage 'stable' 'bar' 'all' '1' '' '' '' 'main/debian-installer/others'
+insertpackage 'stable-backports' 'foo' 'all' '1+sb'
+insertpackage 'stable-backports' 'bar' 'all' '1+sb' '' '' '' 'main/debian-installer/others'
+
+find aptarchive/dists -path '*/debian-installer/i18n/Translation-en*' -delete
+
+setupaptarchive --no-update
+sed -i -e '/^Codename: / a\
+Components: main contrib' $(find ./aptarchive -name 'Release')
+signreleasefiles
+
+testsuccess aptget update
+
+sed -i -e 's# main\w*$# main main/debian-installer#' rootdir/etc/apt/sources.list.d/*
+
+testsuccess aptget update