From dd046131f029dfe43a7b97a62ece9a932b6d8f24 Mon Sep 17 00:00:00 2001
From: Ben S George <73480087+AlbertEinsteinTG@users.noreply.github.com>
Date: Sun, 9 Aug 2026 12:16:20 +0000
Subject: [PATCH] fix(types): name the clashing service and make the error
 stable

CheckContainerNameUnicity tracked seen container names in a
utils.Set[string], which is a map[string]struct{}. Indexing it yields
the zero struct rather than the service that claimed the name, so the
%s verb rendered it as "{}". The format string also ended with an
unbalanced quote:

  services.a: container name "shared" is already in use by service {}"

Track container_name -> declaring service in a map[string]string and
print it with %q so both services are named. Iterate via ServiceNames()
instead of ranging over the map: Go randomises map iteration, so the
same project surfaced a different pair on each run, which made the
error unreproducible in bug reports and impossible to assert exactly.

  services.a: container name "shared" is already in use by service "b"

The existing test asserted a substring ending one word before the
broken segment, so neither defect was covered. It now asserts the
whole message, which the stable ordering makes possible.

Signed-off-by: Ben S George <73480087+AlbertEinsteinTG@users.noreply.github.com>
---
 loader/validate_test.go | 2 +-
 types/project.go        | 9 +++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/loader/validate_test.go b/loader/validate_test.go
index 2dda05eaf..1c5a738d3 100644
--- a/loader/validate_test.go
+++ b/loader/validate_test.go
@@ -277,7 +277,7 @@ func TestValidateContainerName(t *testing.T) {
 		},
 	}
 	err := project.CheckContainerNameUnicity()
-	assert.Assert(t, strings.Contains(err.Error(), `container name "mycontainer" is already in use by`))
+	assert.Assert(t, strings.Contains(err.Error(), `container name "mycontainer" is already in use by service "myservice`))
 }
 
 func TestValidateWatch(t *testing.T) {
diff --git a/types/project.go b/types/project.go
index 66365faed..d82acdea7 100644
--- a/types/project.go
+++ b/types/project.go
@@ -905,13 +905,14 @@ func (p *Project) WithServicesTransform(fn func(name string, s ServiceConfig) (S
 
 // CheckContainerNameUnicity validate project doesn't have services declaring the same container_name
 func (p *Project) CheckContainerNameUnicity() error {
-	names := utils.Set[string]{}
-	for name, s := range p.Services {
+	names := map[string]string{}
+	for _, name := range p.ServiceNames() {
+		s := p.Services[name]
 		if s.ContainerName != "" {
 			if existing, ok := names[s.ContainerName]; ok {
-				return fmt.Errorf(`services.%s: container name %q is already in use by service %s"`, name, s.ContainerName, existing)
+				return fmt.Errorf(`services.%s: container name %q is already in use by service %q`, name, s.ContainerName, existing)
 			}
-			names.Add(s.ContainerName)
+			names[s.ContainerName] = name
 		}
 	}
 	return nil