From fbad48b5d95811b4bc9262736eb02c82a2d07d5e Mon Sep 17 00:00:00 2001
From: Subhomoy Haldar <hungrybluedev@gmail.com>
Date: Mon, 11 Jul 2022 23:38:53 +0530
Subject: [PATCH] v.builder: retain executable after `v run`, if the executable
 was already existing (#15021)

---
 vlib/v/builder/builder.v      |  6 ++++
 vlib/v/builder/builder_test.v | 55 +++++++++++++++++++++++++++++++++++
 vlib/v/builder/compile.v      |  6 ++--
 vlib/v/builder/rebuilding.v   |  2 +-
 4 files changed, 66 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/builder/builder_test.v

diff --git a/vlib/v/builder/builder.v b/vlib/v/builder/builder.v
index f3b0c86223..85db9e736c 100644
--- a/vlib/v/builder/builder.v
+++ b/vlib/v/builder/builder.v
@@ -41,6 +41,7 @@ pub mut:
 	mod_invalidates_mods  map[string][]string // changes in mod `os`, force invalidation of mods, that do `import os`
 	path_invalidates_mods map[string][]string // changes in a .v file from `os`, invalidates `os`
 	crun_cache_keys       []string // target executable + top level source files; filled in by Builder.should_rebuild
+	executable_exists     bool     // if the executable already exists, don't remove new executable after `v run`
 }
 
 pub fn new_builder(pref &pref.Preferences) Builder {
@@ -67,6 +68,10 @@ pub fn new_builder(pref &pref.Preferences) Builder {
 	if pref.show_callgraph || pref.show_depgraph {
 		dotgraph.start_digraph()
 	}
+	mut executable_name := pref.out_name
+	$if windows {
+		executable_name += '.exe'
+	}
 	return Builder{
 		pref: pref
 		table: table
@@ -74,6 +79,7 @@ pub fn new_builder(pref &pref.Preferences) Builder {
 		transformer: transformer.new_transformer_with_table(table, pref)
 		compiled_dir: compiled_dir
 		cached_msvc: msvc
+		executable_exists: os.is_file(executable_name)
 	}
 }
 
diff --git a/vlib/v/builder/builder_test.v b/vlib/v/builder/builder_test.v
new file mode 100644
index 0000000000..354f6f1e1f
--- /dev/null
+++ b/vlib/v/builder/builder_test.v
@@ -0,0 +1,55 @@
+module main
+
+import os
+import arrays
+
+const test_path = 'v_run_check'
+
+fn arrays_are_equivalent(a []string, b []string) bool {
+	if a.len != b.len {
+		return false
+	}
+	for item in a {
+		if item !in b {
+			return false
+		}
+	}
+	return true
+}
+
+fn test_conditional_executable_removal() ? {
+	// Setup the sample project
+	dir := os.join_path(os.temp_dir(), test_path)
+
+	os.rmdir_all(dir) or {}
+	os.mkdir(dir) or {}
+
+	defer {
+		os.rmdir_all(dir) or {}
+	}
+
+	os.chdir(dir)?
+	os.execute_or_exit('${os.quoted_path(@VEXE)} init')
+
+	mut executable := test_path
+	$if windows {
+		executable += '.exe'
+	}
+
+	original_file_list := os.ls(dir)?
+	new_file_list := arrays.concat(original_file_list, executable)
+
+	assert os.execute('${os.quoted_path(@VEXE)} run .').output == 'Hello World!\n'
+
+	assert arrays_are_equivalent(os.ls(dir)?, original_file_list)
+
+	assert os.execute('${os.quoted_path(@VEXE)} .').output == ''
+
+	assert os.execute('./$executable').output == 'Hello World!\n'
+
+	assert arrays_are_equivalent(os.ls(dir)?, new_file_list)
+
+	assert os.execute('${os.quoted_path(@VEXE)} run .').output == 'Hello World!\n'
+
+	assert arrays_are_equivalent(os.ls(dir)?, new_file_list)
+}
diff --git a/vlib/v/builder/compile.v b/vlib/v/builder/compile.v
index 828e397704..a470854522 100644
--- a/vlib/v/builder/compile.v
+++ b/vlib/v/builder/compile.v
@@ -144,8 +144,10 @@ fn (mut v Builder) cleanup_run_executable_after_exit(exefile string) {
 		v.pref.vrun_elog('keeping executable: $exefile , because -keepc was passed')
 		return
 	}
-	v.pref.vrun_elog('remove run executable: $exefile')
-	os.rm(exefile) or {}
+	if !v.executable_exists {
+		v.pref.vrun_elog('remove run executable: $exefile')
+		os.rm(exefile) or {}
+	}
 }
 
 // 'strings' => 'VROOT/vlib/strings'
diff --git a/vlib/v/builder/rebuilding.v b/vlib/v/builder/rebuilding.v
index 44a5773c00..076b958e32 100644
--- a/vlib/v/builder/rebuilding.v
+++ b/vlib/v/builder/rebuilding.v
@@ -259,7 +259,7 @@ fn (mut b Builder) handle_usecache(vexe string) {
 pub fn (mut b Builder) should_rebuild() bool {
 	mut exe_name := b.pref.out_name
 	$if windows {
-		exe_name = exe_name + '.exe'
+		exe_name += '.exe'
 	}
 	if !os.is_file(exe_name) {
 		return true