From 8564df51e5c13b3cc1ecad0c2e0d6c0a633d46f1 Mon Sep 17 00:00:00 2001
From: Rangi42 <sylvie.oukaour+rangi42@gmail.com>
Date: Sun, 24 Aug 2025 16:52:20 -0400
Subject: [PATCH] `-Wexport-undefined` warning for exporting undefined symbols

---
 contrib/bash_compl/_rgbasm.bash | 1 +
 contrib/zsh_compl/_rgbasm       | 1 +
 include/asm/warning.hpp         | 1 +
 man/rgbasm.1                    | 4 ++++
 src/asm/symbol.cpp              | 4 +++-
 src/asm/warning.cpp             | 1 +
 test/asm/export.asm             | 3 +++
 test/asm/export.err             | 9 +++++++++
 8 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/contrib/bash_compl/_rgbasm.bash b/contrib/bash_compl/_rgbasm.bash
index 7ee09752..5377ef00 100755
--- a/contrib/bash_compl/_rgbasm.bash
+++ b/contrib/bash_compl/_rgbasm.bash
@@ -184,6 +184,7 @@ _rgbasm_completions() {
 				empty-data-directive
 				empty-macro-arg
 				empty-strrpl
+				export-undefined
 				large-constant
 				macro-shift
 				nested-comment
diff --git a/contrib/zsh_compl/_rgbasm b/contrib/zsh_compl/_rgbasm
index 8347401c..d65bc88d 100644
--- a/contrib/zsh_compl/_rgbasm
+++ b/contrib/zsh_compl/_rgbasm
@@ -16,6 +16,7 @@ _rgbasm_warnings() {
 		'empty-data-directive:Warn on arg-less d[bwl] in ROM'
 		'empty-macro-arg:Warn on empty macro arg'
 		'empty-strrpl:Warn on calling STRRPL with empty pattern'
+		'export-undefined:Warn on EXPORT of an undefined symbol'
 		'large-constant:Warn on constants too large for a signed 32-bit int'
 		'macro-shift:Warn when shifting macro args part their limits'
 		'nested-comment:Warn on "/*" inside block comments'
diff --git a/include/asm/warning.hpp b/include/asm/warning.hpp
index 56e2cfff..f2f37c73 100644
--- a/include/asm/warning.hpp
+++ b/include/asm/warning.hpp
@@ -23,6 +23,7 @@ enum WarningID {
 	WARNING_EMPTY_DATA_DIRECTIVE, // `db`, `dw` or `dl` directive without data in ROM
 	WARNING_EMPTY_MACRO_ARG,      // Empty macro argument
 	WARNING_EMPTY_STRRPL,         // Empty second argument in `STRRPL`
+	WARNING_EXPORT_UNDEFINED,     // `EXPORT` of an undefined symbol
 	WARNING_LARGE_CONSTANT,       // Constants too large
 	WARNING_MACRO_SHIFT,          // `SHIFT` past available arguments in macro
 	WARNING_NESTED_COMMENT,       // Comment-start delimiter in a block comment
diff --git a/man/rgbasm.1 b/man/rgbasm.1
index ea8acafe..85977395 100644
--- a/man/rgbasm.1
+++ b/man/rgbasm.1
@@ -394,6 +394,10 @@ Warn when
 is called with an empty string as its second argument (the substring to replace).
 This warning is enabled by
 .Fl Wall .
+.It Fl Wexport-undefined
+Warn when exporting an undefined symbol.
+This warning is enabled by
+.Fl Wall .
 .It Fl Wno-large-constant
 Warn when a constant too large to fit in a signed 32-bit integer is encountered.
 .It Fl Wmacro-shift
diff --git a/src/asm/symbol.cpp b/src/asm/symbol.cpp
index 1211f09c..f95af7ca 100644
--- a/src/asm/symbol.cpp
+++ b/src/asm/symbol.cpp
@@ -611,7 +611,7 @@ void sym_Export(std::string const &symName) {
 	if (symName.starts_with('!')) {
 		// LCOV_EXCL_START
 		// The parser does not accept anonymous labels for an `EXPORT` directive
-		error("Anonymous labels cannot be exported");
+		error("Cannot export anonymous label");
 		return;
 		// LCOV_EXCL_STOP
 	}
@@ -620,8 +620,10 @@ void sym_Export(std::string const &symName) {
 
 	// If the symbol doesn't exist, create a ref that can be purged
 	if (!sym) {
+		warning(WARNING_EXPORT_UNDEFINED, "Exporting an undefined symbol `%s`", symName.c_str());
 		sym = sym_Ref(symName);
 	}
+
 	sym->isExported = true;
 }
 
diff --git a/src/asm/warning.cpp b/src/asm/warning.cpp
index ae523bc6..a3772004 100644
--- a/src/asm/warning.cpp
+++ b/src/asm/warning.cpp
@@ -30,6 +30,7 @@ Diagnostics<WarningLevel, WarningID> warnings = {
         {"empty-data-directive", LEVEL_ALL       },
         {"empty-macro-arg",      LEVEL_EXTRA     },
         {"empty-strrpl",         LEVEL_ALL       },
+        {"export-undefined",     LEVEL_ALL       },
         {"large-constant",       LEVEL_DEFAULT   },
         {"macro-shift",          LEVEL_EXTRA     },
         {"nested-comment",       LEVEL_DEFAULT   },
diff --git a/test/asm/export.asm b/test/asm/export.asm
index ce66d3b4..7d9dd54d 100644
--- a/test/asm/export.asm
+++ b/test/asm/export.asm
@@ -16,3 +16,6 @@ EXPORT REDEF variable = 1234
 DEF equs_sym EQUS "hello"
 EXPORT equs_sym ; exports undefined symbol `hello` due to EQUS expansion
 EXPORT DEF string EQUS "goodbye" ; invalid syntax
+
+PURGE equ_sym
+EXPORT equ_sym
diff --git a/test/asm/export.err b/test/asm/export.err
index 516e8e07..7f1b85ff 100644
--- a/test/asm/export.err
+++ b/test/asm/export.err
@@ -1,3 +1,12 @@
+warning: Exporting an undefined symbol `undefined` [-Wexport-undefined]
+    at export.asm(1)
+warning: Exporting an undefined symbol `hello` [-Wexport-undefined]
+    at export.asm(17)
+    while expanding symbol `equs_sym`
 error: syntax error, unexpected EQUS
     at export.asm(18)
+warning: Purging an exported symbol `equ_sym` [-Wpurge]
+    at export.asm(20)
+warning: Exporting an undefined symbol `equ_sym` [-Wexport-undefined]
+    at export.asm(21)
 Assembly aborted with 1 error!