From 7878f0c514fe68bc4587aaf86d424c62213460af Mon Sep 17 00:00:00 2001
From: Tonis Tiigi <tonistiigi@gmail.com>
Date: Thu, 4 Feb 2021 23:27:09 -0800
Subject: [PATCH] bake: allow variables in user functions

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
---
 bake/hcl.go      | 19 ++++++++++---------
 bake/hcl_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/bake/hcl.go b/bake/hcl.go
index 704d244fb7ad..dbca9ce7ed02 100644
--- a/bake/hcl.go
+++ b/bake/hcl.go
@@ -167,15 +167,6 @@ func parseHCL(dt []byte, fn string) (_ *Config, err error) {
 		}
 	}
 
-	userFunctions, _, diags := userfunc.DecodeUserFunctions(file.Body, "function", func() *hcl.EvalContext {
-		return &hcl.EvalContext{
-			Functions: stdlibFunctions,
-		}
-	})
-	if diags.HasErrors() {
-		return nil, diags
-	}
-
 	var sc staticConfig
 
 	// Decode only variable blocks without interpolation.
@@ -189,6 +180,16 @@ func parseHCL(dt []byte, fn string) (_ *Config, err error) {
 		variables[variable.Name] = cty.StringVal(variable.Default)
 	}
 
+	userFunctions, _, diags := userfunc.DecodeUserFunctions(file.Body, "function", func() *hcl.EvalContext {
+		return &hcl.EvalContext{
+			Functions: stdlibFunctions,
+			Variables: variables,
+		}
+	})
+	if diags.HasErrors() {
+		return nil, diags
+	}
+
 	// Override default with values from environment.
 	for _, env := range os.Environ() {
 		parts := strings.SplitN(env, "=", 2)
diff --git a/bake/hcl_test.go b/bake/hcl_test.go
index 6cb53ea392c6..ebe74bb630f7 100644
--- a/bake/hcl_test.go
+++ b/bake/hcl_test.go
@@ -250,4 +250,36 @@ func TestParseHCL(t *testing.T) {
 		require.Error(t, err)
 		require.Contains(t, err.Error(), "docker-bake.hcl:7,17-37: Variables not allowed; Variables may not be used here.")
 	})
+
+	t.Run("WithVariablesInFunctions", func(t *testing.T) {
+		dt := []byte(`
+		variable "REPO" {
+			default = "user/repo"
+		}
+		function "tag" {
+			params = [tag]
+			result = ["${REPO}:${tag}"]
+		}
+
+		target "webapp" {
+			tags = tag("v1")
+		}
+		`)
+
+		c, err := ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "webapp")
+		require.Equal(t, []string{"user/repo:v1"}, c.Targets[0].Tags)
+
+		os.Setenv("REPO", "docker/buildx")
+
+		c, err = ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "webapp")
+		require.Equal(t, []string{"docker/buildx:v1"}, c.Targets[0].Tags)
+	})
 }