From 5311af3bfc0f80f0e86bbb1f8b4066184aec8031 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@datawire.io>
Date: Sat, 31 Aug 2019 14:28:26 -0400
Subject: [PATCH] prelude_str.mk: Add a 'str.eq' function

---
 prelude.mk             |  1 +
 prelude_str.mk         |  4 ++++
 tests/prelude_str.bats | 26 ++++++++++++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/prelude.mk b/prelude.mk
index 8ce60a6536..acb2f6da59 100644
--- a/prelude.mk
+++ b/prelude.mk
@@ -16,6 +16,7 @@
 #  String support:
 #  - Variable: export NL
 #  - Variable:        SPACE
+#  - Function: str.eq
 #
 #  Path support:
 #  - Function: path.trimprefix
diff --git a/prelude_str.mk b/prelude_str.mk
index 9ac84b0e86..966fcd3e76 100644
--- a/prelude_str.mk
+++ b/prelude_str.mk
@@ -15,3 +15,7 @@ export NL
 define SPACE
  
 endef
+
+# Usage: $(call str.eq,STR1,STR2)
+# Evaluates to either $(TRUE) or $(FALSE)
+str.eq = $(if $(subst x$1,,x$2)$(subst x$2,,x$1),$(FALSE),$(TRUE))
diff --git a/tests/prelude_str.bats b/tests/prelude_str.bats
index 62be2f726c..59850e2ecd 100644
--- a/tests/prelude_str.bats
+++ b/tests/prelude_str.bats
@@ -11,3 +11,29 @@ load common
 	# Honestly, this checks `quote.shell` more than it does SPACE.
 	check_expr_eq strict '$(SPACE)' ' '
 }
+
+@test "prelude_str.mk: str.eq" {
+	cat >>Makefile <<-'__EOT__'
+		include build-aux/prelude.mk
+		test = $(info ("$1" == "$2") => $(if $(call str.eq,$1,$2),$$(TRUE),$$(FALSE)))
+		$(call test,foo,foo)
+		$(call test,foo,bar)
+		$(call test,bar,bar)
+		$(call test,f%,foo)
+		$(call test,foo,f%)
+		$(call test,f%,f%)
+		all: noop
+		noop: ; @true
+		.PHONY: noop
+	__EOT__
+
+	make >actual
+	printf '("%s" == "%s") => $(%s)\n' >expected \
+	       foo foo TRUE \
+	       foo bar FALSE \
+	       bar bar TRUE \
+	       f% foo FALSE \
+	       foo f% FALSE \
+	       f% f% TRUE
+	diff -u expected actual
+}