From 40c6be70076365e0bc2b69e4368b7338a2e452a8 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 29 Dec 2019 14:01:22 +0000
Subject: [PATCH] Warnings: Introduce new `broken-var-ref' warning

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 README                       | 5 +++++
 generate                     | 5 +++++
 tests/filter/Dir.mk.expected | 2 ++
 tests/filter/Dir.sd.mk       | 2 ++
 tests/filter/stderr.expected | 1 +
 5 files changed, 15 insertions(+)

diff --git a/README b/README
index a44fb49..e303788 100644
--- a/README
+++ b/README
@@ -336,6 +336,11 @@ suppressed with the &:warn directive.  The warning tags are:
 	by more letters.  Note that &$FOO works differently to
 	raw make: it expands to $(sub_dir_FOO).
 
+    broken-var-ref
+        An attempt at variable expansion looking like $&...
+	You probably expected this to mean $(TOP_F)BAR but it
+	expands to $TOP_FBAR which make thinks means $(T)OP_FBAR.
+
     unknown-warning
 	&:warn was used to try to enable a warning that this version
 	of subdirmk does not understand.  (Note that an attempt to
diff --git a/generate b/generate
index bae0995..5106129 100755
--- a/generate
+++ b/generate
@@ -177,6 +177,7 @@ our @warn_ena_dfl = map { $_ => 1 } qw(
     local+global
     single-char-var
     unknown-warning
+    broken-var-ref
 );
 our %warn_ena = @warn_ena_dfl;
 
@@ -332,6 +333,10 @@ sub process_input_mk ($$$$) {
 		    wrn 'single-char-var',
 		    'possibly confusing unbracketed single-char $-expansion';
 		}
+		elsif (m{^$esc}) {
+		    wrn 'broken-var-ref',
+		    'broken $&... expansion; you probably meant &$';
+		}
 		elsif (m{^\(($esc)?([^()\$]+)\)} ||
 		       m{^\{($esc)?([^{}\$]+)\}}) {
 		    $note_varref->($2,!!$1);
diff --git a/tests/filter/Dir.mk.expected b/tests/filter/Dir.mk.expected
index 7eecb23..5205a3a 100644
--- a/tests/filter/Dir.mk.expected
+++ b/tests/filter/Dir.mk.expected
@@ -17,6 +17,8 @@ TOP_WARN += 3
 
 ${eval ${call  some-macro, 42, $$x, {  $(foreach something) } }}
 
+$TOP_FBAR
+
 # doctests:
 # Suffix in .
 
diff --git a/tests/filter/Dir.sd.mk b/tests/filter/Dir.sd.mk
index 1a4eb1f..c97ee0f 100644
--- a/tests/filter/Dir.sd.mk
+++ b/tests/filter/Dir.sd.mk
@@ -16,5 +16,7 @@ WARN += 3
 
 &${ some-macro, 42, $x, { &$- $(foreach something) } }
 
+$&FBAR
+
 # doctests:
 &:include &doctests.sd.mk
diff --git a/tests/filter/stderr.expected b/tests/filter/stderr.expected
index fe8b3f2..76e32dd 100644
--- a/tests/filter/stderr.expected
+++ b/tests/filter/stderr.expected
@@ -1,5 +1,6 @@
 subdirmk: warning (unknown-warning): ./Prefix.sd.mk:2: unknown warning many-requests-for-unknown-warning requested
 subdirmk: warning (single-char-var): ./Dir.sd.mk:8: possibly confusing unbracketed single-char $-expansion
+subdirmk: warning (broken-var-ref): ./Dir.sd.mk:19: broken $&... expansion; you probably meant &$
 subdirmk: warning (local+global): saw both WARN and &WARN
  saw WARN at ./Dir.sd.mk:6
  saw WARN at ./Dir.sd.mk:9
-- 
2.30.2