From df724f5827e2b96d53a708d642ee52798506915c Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Sat, 12 Oct 2024 10:33:24 +0200
Subject: [PATCH] loader: don't panic when main package is not named 'main'

This can in fact happen in practice, so return an actual error message
instead.
---
 errors_test.go                 | 1 +
 loader/loader.go               | 8 ++++++--
 testdata/errors/invalidmain.go | 6 ++++++
 3 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 testdata/errors/invalidmain.go

diff --git a/errors_test.go b/errors_test.go
index 62d5af2cb..5045840ff 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -24,6 +24,7 @@ func TestErrors(t *testing.T) {
 		{name: "cgo"},
 		{name: "compiler"},
 		{name: "interp"},
+		{name: "invalidmain"},
 		{name: "linker-flashoverflow", target: "cortex-m-qemu"},
 		{name: "linker-ramoverflow", target: "cortex-m-qemu"},
 		{name: "linker-undefined", target: "darwin/arm64"},
diff --git a/loader/loader.go b/loader/loader.go
index d10485707..6786ee533 100644
--- a/loader/loader.go
+++ b/loader/loader.go
@@ -418,8 +418,12 @@ func (p *Package) Check() error {
 	packageName := p.ImportPath
 	if p == p.program.MainPkg() {
 		if p.Name != "main" {
-			// Sanity check. Should not ever trigger.
-			panic("expected main package to have name 'main'")
+			return Errors{p, []error{
+				scanner.Error{
+					Pos: p.program.fset.Position(p.Files[0].Name.Pos()),
+					Msg: fmt.Sprintf("expected main package to have name \"main\", not %#v", p.Name),
+				},
+			}}
 		}
 		packageName = "main"
 	}
diff --git a/testdata/errors/invalidmain.go b/testdata/errors/invalidmain.go
new file mode 100644
index 000000000..a86e32c8d
--- /dev/null
+++ b/testdata/errors/invalidmain.go
@@ -0,0 +1,6 @@
+// some comment to move the first line
+
+package foobar
+
+// ERROR: # command-line-arguments
+// ERROR: invalidmain.go:3:9: expected main package to have name "main", not "foobar"