From f6652f4f186d11df7b09965e16fc850516962d8e Mon Sep 17 00:00:00 2001
From: Youkichi Hosoi <youkichihosoi@google.com>
Date: Wed, 1 Apr 2020 05:07:24 +0900
Subject: [PATCH] strings.mk: Allow empty RHS values for inputs of
 collapse-pairs

This CL is to make the function collapse-pairs(), which is applied to
lists of "property=value" pairs, allow empty properties (i.e. lines of
the form "empty.prop=").
Currently, the function only allows empty properties at the end (see
https://android-review.googlesource.com/c/platform/build/+/722908).
So empty properties in the middle result in broken property files (e.g.
"a=b c= d=e" is transformed to "a=b c=d=e", in which the property "c",
which originally has no value, is interpreted as having the value "d=e",
whereas the property "d", which originally has the value "e", is missing
from the resulting property file).
This CL revises the function so as to keep empty properties in the
middle as is (e.g. it returns "a=b c= d=e" for the above example), while
preserving the behavior for well-formed lists like "a=b c= d e = f".

Bug: 152379493
Test: make
Change-Id: I35faeaedc3bc42e56e01201baf7ea6805a610439
---
 common/strings.mk | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/common/strings.mk b/common/strings.mk
index ce6d6fbe9f..ba20e272c0 100644
--- a/common/strings.mk
+++ b/common/strings.mk
@@ -88,7 +88,7 @@ $(word $(1),$(subst :,$(space),$(2)))
 endef
 
 ###########################################################
-## Convert "a=b c= d e = f" into "a=b c=d e=f"
+## Convert "a=b c= d e = f = g h=" into "a=b c=d e= f=g h="
 ##
 ## $(1): list to collapse
 ## $(2): if set, separator word; usually "=", ":", or ":="
@@ -96,11 +96,29 @@ endef
 ###########################################################
 
 define collapse-pairs
+$(strip \
 $(eval _cpSEP := $(strip $(if $(2),$(2),=)))\
-$(strip $(subst $(space)$(_cpSEP)$(space),$(_cpSEP),$(strip \
-    $(subst $(_cpSEP), $(_cpSEP) ,$(1)))$(space)))
+$(eval _cpLHS :=)\
+$(eval _cpRET :=)\
+$(foreach w,$(subst $(space)$(_cpSEP),$(_cpSEP),$(strip \
+            $(subst $(_cpSEP),$(space)$(_cpSEP)$(space),$(1)))),\
+  $(if $(findstring $(_cpSEP),$(w)),\
+    $(eval _cpRET += $(_cpLHS))$(eval _cpLHS := $(w)),\
+    $(eval _cpRET += $(_cpLHS)$(w))$(eval _cpLHS :=)))\
+$(if $(_cpLHS),$(_cpRET)$(space)$(_cpLHS),$(_cpRET))\
+$(eval _cpSEP :=)\
+$(eval _cpLHS :=)\
+$(eval _cpRET :=))
 endef
 
+# Sanity check for collapse-pairs.
+ifneq (a=b c=d e= f=g h=,$(call collapse-pairs,a=b c= d e = f = g h=))
+  $(error collapse-pairs sanity check failure)
+endif
+ifneq (a:=b c:=d e:=f g:=h,$(call collapse-pairs,a:=b c:= d e :=f g := h,:=))
+  $(error collapse-pairs sanity check failure)
+endif
+
 ###########################################################
 ## Given a list of pairs, if multiple pairs have the same
 ## first components, keep only the first pair.