From 61928bd882f3b53ebd88862bc9bb40f2bb33ca0d Mon Sep 17 00:00:00 2001
From: Zackery Spytz <zspytz@gmail.com>
Date: Sat, 7 Dec 2019 21:08:11 -0700
Subject: [PATCH 1/4] Add support for C++20 "templated" lambdas

Such as `auto lambda = []<typename T>(std::vector<T> t){};`
---
 Source/CParse/parser.y | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/Source/CParse/parser.y b/Source/CParse/parser.y
index be5159a62..a8456826b 100644
--- a/Source/CParse/parser.y
+++ b/Source/CParse/parser.y
@@ -1713,7 +1713,7 @@ static String *add_qualifier_to_declarator(SwigType *type, SwigType *qualifier)
 %type <ptype>    type_specifier primitive_type_list ;
 %type <node>     fname stringtype;
 %type <node>     featattr;
-%type <node>     lambda_introducer lambda_body;
+%type <node>     lambda_introducer lambda_body lambda_template;
 %type <pl>       lambda_tail;
 %type <str>      virt_specifier_seq virt_specifier_seq_opt;
 
@@ -3420,17 +3420,17 @@ cpp_alternate_rettype : primitive_type { $$ = $1; }
    auto myFunc = [](int x, int y) throw() -> int { return x+y; };
    auto six = [](int x, int y) { return x+y; }(4, 2);
    ------------------------------------------------------------ */
-cpp_lambda_decl : storage_class AUTO idcolon EQUAL lambda_introducer LPAREN parms RPAREN cpp_const lambda_body lambda_tail {
+cpp_lambda_decl : storage_class AUTO idcolon EQUAL lambda_introducer lambda_template LPAREN parms RPAREN cpp_const lambda_body lambda_tail {
 		  $$ = new_node("lambda");
 		  Setattr($$,"name",$3);
 		  add_symbols($$);
 	        }
-                | storage_class AUTO idcolon EQUAL lambda_introducer LPAREN parms RPAREN cpp_const ARROW type lambda_body lambda_tail {
+                | storage_class AUTO idcolon EQUAL lambda_introducer lambda_template LPAREN parms RPAREN cpp_const ARROW type lambda_body lambda_tail {
 		  $$ = new_node("lambda");
 		  Setattr($$,"name",$3);
 		  add_symbols($$);
 		}
-                | storage_class AUTO idcolon EQUAL lambda_introducer lambda_body lambda_tail {
+                | storage_class AUTO idcolon EQUAL lambda_introducer lambda_template lambda_body lambda_tail {
 		  $$ = new_node("lambda");
 		  Setattr($$,"name",$3);
 		  add_symbols($$);
@@ -3442,7 +3442,12 @@ lambda_introducer : LBRACKET {
 		  $$ = 0;
 	        }
 		;
-
+lambda_template : LESSTHAN {
+		  skip_balanced('<','>');
+		  $$ = 0;
+              }
+              | empty { $$ = 0; }
+              ;
 lambda_body : LBRACE {
 		  skip_balanced('{','}');
 		  $$ = 0;

From e31de2aebba03425915dd9f399c60e9ec85a8ef4 Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Wed, 27 Jul 2022 09:30:30 +1200
Subject: [PATCH 2/4] Tidy up indentation

---
 Source/CParse/parser.y | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Source/CParse/parser.y b/Source/CParse/parser.y
index a8456826b..816264de6 100644
--- a/Source/CParse/parser.y
+++ b/Source/CParse/parser.y
@@ -3442,12 +3442,14 @@ lambda_introducer : LBRACKET {
 		  $$ = 0;
 	        }
 		;
+
 lambda_template : LESSTHAN {
 		  skip_balanced('<','>');
 		  $$ = 0;
-              }
-              | empty { $$ = 0; }
-              ;
+		}
+		| empty { $$ = 0; }
+		;
+
 lambda_body : LBRACE {
 		  skip_balanced('{','}');
 		  $$ = 0;

From 88f227b5da97bd30ab165a000530bb7468f96424 Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Wed, 27 Jul 2022 09:30:39 +1200
Subject: [PATCH 3/4] Add testcase

---
 Examples/test-suite/common.mk               |  1 +
 Examples/test-suite/cpp20_lambda_template.i | 12 ++++++++++++
 2 files changed, 13 insertions(+)
 create mode 100644 Examples/test-suite/cpp20_lambda_template.i

diff --git a/Examples/test-suite/common.mk b/Examples/test-suite/common.mk
index 838ea5d2a..6ca3aef22 100644
--- a/Examples/test-suite/common.mk
+++ b/Examples/test-suite/common.mk
@@ -649,6 +649,7 @@ CPP17_TEST_BROKEN = \
 
 # C++20 test cases.
 CPP20_TEST_CASES += \
+	cpp20_lambda_template \
 	cpp20_spaceship_operator \
 
 # Broken C++20 test cases.
diff --git a/Examples/test-suite/cpp20_lambda_template.i b/Examples/test-suite/cpp20_lambda_template.i
new file mode 100644
index 000000000..948364f42
--- /dev/null
+++ b/Examples/test-suite/cpp20_lambda_template.i
@@ -0,0 +1,12 @@
+%module cpp20_lambda_template
+
+// We just want to test that SWIG doesn't choke parsing this so suppress:
+// Warning 340: Lambda expressions and closures are not fully supported yet.
+%warnfilter(WARN_CPP11_LAMBDA);
+
+%include <std_vector.i>
+
+%inline %{
+#include <vector>
+auto templated_lambda = []<typename T>(std::vector<T> t){};
+%}

From 8182740b8e6f89c276d19b767853f89b74a3c569 Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Wed, 27 Jul 2022 09:34:16 +1200
Subject: [PATCH 4/4] Add documentation

---
 CHANGES.current             | 3 +++
 Doc/Manual/CPlusPlus20.html | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/CHANGES.current b/CHANGES.current
index 38c0b7011..fbf85ba3e 100644
--- a/CHANGES.current
+++ b/CHANGES.current
@@ -7,6 +7,9 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2022-07-27: ZackerySpytz, olly
+	    #1678 Support parsing C++20 templated lambdas.
+
 2022-07-27: ZackerySpytz, olly
 	    #1622 Add support for the C++20 spaceship operator (<=>).
 
diff --git a/Doc/Manual/CPlusPlus20.html b/Doc/Manual/CPlusPlus20.html
index 8db84bfd5..0f29a03b8 100644
--- a/Doc/Manual/CPlusPlus20.html
+++ b/Doc/Manual/CPlusPlus20.html
@@ -50,6 +50,14 @@ or attempts to automatically map it to a three-way comparison operator
 in any target languages that have one.
 </p>
 
+<H3><a name="CPlusPlus20_lambda_templates">10.2.2 Lambda templates</a></H3>
+
+<p>
+SWIG should parse lambda templates, but
+<a href="CPlusPlus11.html#CPlusPlus11_lambda_functions_and_expressions">like
+    non-templated lambdas they aren't currently wrapped</a>.
+</p>
+
 <H2><a name="CPlusPlus20_standard_library_changes">10.3 Standard library changes</a></H2>