From 8ce8973e58272cd80ff658488744429851e16197 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81kos=20Tak=C3=A1cs?= <takacs.akos@it-sziget.hu>
Date: Sun, 20 Mar 2022 17:48:57 +0100
Subject: [PATCH] Fix required env vars ignored except the last one
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During the variable substitution, if a missing variable was followed
by an existing one, the empty "outerErr" variable overwrote the previous
non-empty variable.

Unlike with Docker Compose v1, the first found error did not guarantee
that an actual error would be thrown.

Example which would have run before the fix even though var1 is not defined:

```yaml
services:
  bash:
    image: bash:5.0.18-alpine3.15
    environment:
      var12: "_ ${var1:?Error1} _ ${var2:?Error2} _ "
    command:
      - env
```

```bash
```

This change also means that, if multiple variables are missing in one string, the first one will be reported by Docker Compose

Signed-off-by: Ákos Takács <takacs.akos@it-sziget.hu>
---
 interpolation/interpolation_test.go | 1 +
 template/template.go                | 9 ++++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/interpolation/interpolation_test.go b/interpolation/interpolation_test.go
index b67eee40..85027311 100644
--- a/interpolation/interpolation_test.go
+++ b/interpolation/interpolation_test.go
@@ -114,6 +114,7 @@ func TestValidUnexistentInterpolation(t *testing.T) {
 		{test: "{{{ ${FOO:?foo_} }}}", errMsg: "foo_"},
 		{test: "{{{ ${FOO:?foo-bar-value} }}}", errMsg: "foo-bar-value"},
 		{test: "{{{ ${FOO:?foo} ${BAR:-DEFAULT_VALUE} }}}", errMsg: "foo"},
+		{test: "${FOO:?foo} ${BAR:?bar}", errMsg: "foo"},
 		{test: "{{{ ${BAR} }}}", expected: "{{{  }}}"},
 		{test: "${FOO:?baz} }}}", errMsg: "baz"},
 		{test: "${FOO?baz} }}}", errMsg: "baz"},
diff --git a/template/template.go b/template/template.go
index 1e497ab3..7056a13a 100644
--- a/template/template.go
+++ b/template/template.go
@@ -62,6 +62,7 @@ type SubstituteFunc func(string, Mapping) (string, bool, error)
 // It accepts additional substitute function.
 func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, subsFuncs ...SubstituteFunc) (string, error) {
 	var outerErr error
+	var returnErr error
 
 	result := pattern.ReplaceAllStringFunc(template, func(substring string) string {
 		_, subsFunc := getSubstitutionFunctionForTemplate(substring)
@@ -91,6 +92,9 @@ func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, su
 
 		if substitution == "" {
 			outerErr = &InvalidTemplateError{Template: template}
+			if returnErr == nil {
+				returnErr = outerErr
+			}
 			return ""
 		}
 
@@ -101,6 +105,9 @@ func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, su
 			)
 			value, applied, outerErr = subsFunc(substitution, mapping)
 			if outerErr != nil {
+				if returnErr == nil {
+					returnErr = outerErr
+				}
 				return ""
 			}
 			if applied {
@@ -119,7 +126,7 @@ func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, su
 		return value
 	})
 
-	return result, outerErr
+	return result, returnErr
 }
 
 func getSubstitutionFunctionForTemplate(template string) (string, SubstituteFunc) {