executor: expand args in build logs

Expand user,builtin and heading args before logging build steps.

Closes: #6327

Signed-off-by: flouthoc <[email protected]>

Author: flouthoc

imagebuildah/executor.go

@@ -600,7 +600,19 @@ func (b *Executor) buildStage(ctx context.Context, cleanupStages map[int]*StageE
 				prefix += ": "
 			}
 			suffix := "\n"
-			fmt.Fprintf(stageExecutor.executor.out, prefix+format+suffix, args...)
+			builtinArgs := argsMapToSlice(stage.Builder.BuiltinArgDefaults)
+			headingArgs := argsMapToSlice(stage.Builder.HeadingArgs)
+			userArgs := argsMapToSlice(stage.Builder.Args)
+			userArgs = append(builtinArgs, append(userArgs, headingArgs...)...)
+			argsCopy := args
+			for i, _ := range args {
+				argsCopy[i], err = imagebuilder.ProcessWord(args[i].(string), userArgs)
+				if err != nil {
+					argsCopy[i] = args[i]
+					fmt.Printf("while replacing arg variables with values for format in logging %q: %w\n", args[i], err)
+				}
+			}
+			fmt.Fprintf(stageExecutor.executor.out, prefix+format+suffix, argsCopy...)
 		}
 	}
 	b.stagesLock.Unlock()

tests/bud.bats

@@ -8844,3 +8844,42 @@ _EOF
   run_buildah build --layers ${contextdir}
   run_buildah build ${contextdir}
 }
+
+@test "bud build argument expansion in log" {
+  _prefetch alpine
+  target=build-arg-expand-log
+
+  # Test basic build argument expansion
+  run_buildah build $WITH_POLICY_JSON -t ${target} --build-arg foo=foovalue -f $BUDFILES/build-arg/Dockerfile $BUDFILES/build-arg
+  expect_output --substring "RUN echo foovalue"
+
+  # Test with a more complex build argument
+  run_buildah build $WITH_POLICY_JSON -t ${target}-complex --build-arg foo="/usr/local/bin" -f $BUDFILES/build-arg/Dockerfile $BUDFILES/build-arg
+  expect_output --substring "RUN echo /usr/local/bin"
+
+  # Test with multiple build arguments
+  contextdir=${TEST_SCRATCH_DIR}/build-arg-expansion
+  mkdir -p $contextdir
+
+  cat > $contextdir/Containerfile << _EOF
+FROM alpine
+ARG NEWROOT
+ARG PREFIX
+RUN mkdir \$NEWROOT
+RUN echo \$PREFIX/bin
+_EOF
+
+  run_buildah build $WITH_POLICY_JSON -t ${target}-multi --build-arg NEWROOT=/new-root-fs --build-arg PREFIX=/usr $contextdir
+  expect_output --substring "RUN mkdir /new-root-fs"
+  expect_output --substring "RUN echo /usr/bin"
+
+  # Test that unexpanded variables show as empty when no build-arg is provided
+  cat > $contextdir/Containerfile2 << _EOF
+FROM alpine
+ARG UNDEFINEDVAR
+RUN echo \$UNDEFINEDVAR
+_EOF
+
+  run_buildah build $WITH_POLICY_JSON -t ${target}-undefined -f $contextdir/Containerfile2 $contextdir
+  expect_output --substring "RUN echo "
+}