https://github.com/ccache/ccache/commit/2d720aed1843b47aafb2af8bfd15139228545e2b.patch
https://bugs.gentoo.org/751355

From 2d720aed1843b47aafb2af8bfd15139228545e2b Mon Sep 17 00:00:00 2001
From: Joel Rosdahl <joel@rosdahl.net>
Date: Wed, 16 Jun 2021 18:19:04 +0200
Subject: [PATCH] =?UTF-8?q?Don=E2=80=99t=20crash=20on=20relative=20PWD=20v?=
 =?UTF-8?q?alue?=
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Even though PWD “shall represent an absolute pathname of the current
working directory”[1], we shouldn’t crash if a user sets it to a
relative path.

[1]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03

Fixes #860.
---
 src/Util.cpp             |  2 +-
 test/run                 |  1 +
 test/suites/basedir.bash | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

--- a/src/Util.cpp
+++ b/src/Util.cpp
@@ -617,7 +617,7 @@ get_apparent_cwd(const std::string& actual_cwd)
   return actual_cwd;
 #else
   auto pwd = getenv("PWD");
-  if (!pwd) {
+  if (!pwd || !Util::is_absolute_path(pwd)) {
     return actual_cwd;
   }
 
--- a/test/run
+++ b/test/run
@@ -356,6 +356,7 @@ reset_environment() {
     unset TERM
     unset XDG_CACHE_HOME
     unset XDG_CONFIG_HOME
+    export PWD=$(pwd)
 
     export CCACHE_DETECT_SHEBANG=1
     export CCACHE_DIR=$ABS_TESTDIR/.ccache
--- a/test/suites/basedir.bash
+++ b/test/suites/basedir.bash
@@ -311,4 +311,36 @@ EOF
         expect_stat 'cache miss' 1
         expect_equal_content reference.stderr ccache.stderr
     fi
+
+    # -------------------------------------------------------------------------
+    TEST "Relative PWD"
+
+    cd dir1
+    CCACHE_BASEDIR="$(pwd)" PWD=. $CCACHE_COMPILE -I$(pwd)/include -c src/test.c
+    expect_stat 'cache hit (direct)' 0
+    expect_stat 'cache hit (preprocessed)' 0
+    expect_stat 'cache miss' 1
+
+    cd ../dir2
+    CCACHE_BASEDIR="$(pwd)" PWD=. $CCACHE_COMPILE -I$(pwd)/include -c src/test.c
+    expect_stat 'cache hit (direct)' 1
+    expect_stat 'cache hit (preprocessed)' 0
+    expect_stat 'cache miss' 1
+
+    # -------------------------------------------------------------------------
+    TEST "Unset PWD"
+
+    unset PWD
+
+    cd dir1
+    CCACHE_BASEDIR="$(pwd)" $CCACHE_COMPILE -I$(pwd)/include -c src/test.c
+    expect_stat 'cache hit (direct)' 0
+    expect_stat 'cache hit (preprocessed)' 0
+    expect_stat 'cache miss' 1
+
+    cd ../dir2
+    CCACHE_BASEDIR="$(pwd)" $CCACHE_COMPILE -I$(pwd)/include -c src/test.c
+    expect_stat 'cache hit (direct)' 1
+    expect_stat 'cache hit (preprocessed)' 0
+    expect_stat 'cache miss' 1
 }