From e256f1b2aa7db0c2bd7d0ca54f4175f7e4d5718f Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Wed, 22 Dec 2021 16:16:10 +0200
Subject: [PATCH] checker,cgen: stabilise generic method handling (fix a source
 code ordering issue)

---
 vlib/v/ast/ast.v                             |  1 +
 vlib/v/checker/checker.v                     | 13 ++++++++--
 vlib/v/checker/fn.v                          |  2 ++
 vlib/v/gen/c/cgen.v                          |  4 +++
 vlib/v/gen/c/fn.v                            |  9 ++++++-
 vlib/v/tests/generics_method_ordering_test.v | 27 ++++++++++++++++++++
 6 files changed, 53 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/tests/generics_method_ordering_test.v

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 52ffb87f9b..3d82b6ea1c 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -488,6 +488,7 @@ pub mut:
 	return_type_pos   token.Position // `string` in `fn (u User) name() string` position
 	has_return        bool
 	should_be_skipped bool           // true, when -skip-unused could not find any usages of that function, starting from main + other known used functions
+	ninstances        int  // 0 for generic functions with no concrete instances
 	has_await         bool // 'true' if this function uses JS.await
 	//
 	comments      []Comment // comments *after* the header, but *before* `{`; used for InterfaceDecl
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index e80a05dce5..6e1ecfbfd1 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -291,7 +291,7 @@ pub fn (mut c Checker) check_files(ast_files []&ast.File) {
 	c.timers.start('checker_post_process_generic_fns')
 	last_file := c.file
 	// post process generic functions. must be done after all files have been
-	// checked, to eunsure all generic calls are processed as this information
+	// checked, to ensure all generic calls are processed as this information
 	// is needed when the generic type is auto inferred from the call argument
 	// Check more times if there are more new registered fn concrete types
 	for {
@@ -4831,7 +4831,11 @@ fn (mut c Checker) post_process_generic_fns() {
 	for i in 0 .. c.file.generic_fns.len {
 		mut node := c.file.generic_fns[i]
 		c.mod = node.mod
-		for concrete_types in c.table.fn_generic_types[node.name] {
+		gtypes := c.table.fn_generic_types[node.name]
+		$if trace_post_process_generic_fns ? {
+			eprintln('> post_process_generic_fns $node.mod | $node.name | $gtypes')
+		}
+		for concrete_types in gtypes {
 			c.table.cur_concrete_types = concrete_types
 			c.fn_decl(mut node)
 			if node.name == 'vweb.run' {
@@ -4843,6 +4847,11 @@ fn (mut c Checker) post_process_generic_fns() {
 			}
 		}
 		c.table.cur_concrete_types = []
+		$if trace_post_process_generic_fns ? {
+			if node.generic_names.len > 0 {
+				eprintln('       > fn_decl node.name: $node.name | generic_names: $node.generic_names | ninstances: $node.ninstances')
+			}
+		}
 	}
 }
 
diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 6a8fff321f..295b89c518 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -14,8 +14,10 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 		// have a chance to populate c.table.fn_generic_types with
 		// the correct concrete types.
 		c.file.generic_fns << node
+		c.need_recheck_generic_fns = true
 		return
 	}
+	node.ninstances++
 	// save all the state that fn_decl or inner  statements/expressions
 	// could potentially modify, since functions can be nested, due to
 	// anonymous function support, and ensure that it is restored, when
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 46580faa64..8a3b571dfc 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4855,6 +4855,10 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 			has_semicolon = true
 		}
 	} else if node.exprs.len >= 1 {
+		if node.types.len == 0 {
+			g.checker_bug('node.exprs.len == $node.exprs.len && node.types.len == 0',
+				node.pos)
+		}
 		// normal return
 		return_sym := g.table.sym(node.types[0])
 		expr0 := node.exprs[0]
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 2de86347b6..b4384b7c31 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -32,6 +32,12 @@ fn (mut g Gen) fn_decl(node ast.FnDecl) {
 	if node.should_be_skipped {
 		return
 	}
+	if node.ninstances == 0 && node.generic_names.len > 0 {
+		$if trace_generics ? {
+			eprintln('skipping generic fn with no concrete instances: $node.mod $node.name')
+		}
+		return
+	}
 	if !g.is_used_by_main(node) {
 		return
 	}
@@ -82,7 +88,8 @@ fn (mut g Gen) fn_decl(node ast.FnDecl) {
 	if node.is_main {
 		g.has_main = true
 	}
-	is_backtrace := node.name.starts_with('backtrace') // TODO PERF remove this from here
+	// TODO PERF remove this from here
+	is_backtrace := node.name.starts_with('backtrace')
 		&& node.name in ['backtrace_symbols', 'backtrace', 'backtrace_symbols_fd']
 	if is_backtrace {
 		g.write('\n#ifndef __cplusplus\n')
diff --git a/vlib/v/tests/generics_method_ordering_test.v b/vlib/v/tests/generics_method_ordering_test.v
new file mode 100644
index 0000000000..c3c1d678ca
--- /dev/null
+++ b/vlib/v/tests/generics_method_ordering_test.v
@@ -0,0 +1,27 @@
+struct Foo<T> {
+	x int
+}
+
+fn (f Foo<T>) pop() {
+	println('hey')
+}
+
+struct Bar<T> {
+	y int
+}
+
+// NB: Bar.foo before Bar.pop, should not cause a V compiler panic
+fn (b Bar<T>) foo() bool {
+	return true
+}
+
+fn (b Bar<T>) pop() {
+	println(b.foo())
+}
+
+// fn dummy() { println(Bar<int>{}) }
+
+fn test_foo() {
+	dump(Foo<int>{})
+	assert true
+}