fix(format): preserve indentation on recipe continuation lines

internal/handler/format_test.go

@@ -0,0 +1,144 @@
+package handler
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatMakefileContinuations(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{
+			name:  "preserves extra indentation on a continuation line",
+			input: "target:\n\techo a \\\n\t\techo b\n",
+			want:  "target:\n\techo a \\\n\t\techo b\n",
+		},
+		{
+			name:  "preserves indentation across multiple continuations",
+			input: "target:\n\tdocker run \\\n\t\t--rm \\\n\t\t-v $(PWD):/src \\\n\t\timage\n",
+			want:  "target:\n\tdocker run \\\n\t\t--rm \\\n\t\t-v $(PWD):/src \\\n\t\timage\n",
+		},
+		{
+			name:  "preserves varying indentation depths within one logical line",
+			input: "target:\n\tcmd \\\n\t\t--one \\\n\t\t\t--two \\\n\t--three\n",
+			want:  "target:\n\tcmd \\\n\t\t--one \\\n\t\t\t--two \\\n\t--three\n",
+		},
+		{
+			name:  "handles several continued commands in one recipe",
+			input: "target:\n\tfirst \\\n\t\ta\n\tplain\n\tsecond \\\n\t\tb\n",
+			want:  "target:\n\tfirst \\\n\t\ta\n\tplain\n\tsecond \\\n\t\tb\n",
+		},
+		{
+			name:  "does not add indentation when the author used none",
+			input: "target:\n\techo a \\\n\techo b\n",
+			want:  "target:\n\techo a \\\n\techo b\n",
+		},
+		{
+			name:  "adds the missing tab but keeps space indentation on continuations",
+			input: "target:\n\techo a \\\n    echo b\n",
+			want:  "target:\n\techo a \\\n\t    echo b\n",
+		},
+		{
+			name:  "still normalises space indentation on non-continuation recipe lines",
+			input: "target:\n    echo a\n        echo b\n",
+			want:  "target:\n\techo a\n\techo b\n",
+		},
+		{
+			name:  "trims trailing whitespace after a continuation backslash",
+			input: "target:\n\techo a \\\n\t\techo b   \n",
+			want:  "target:\n\techo a \\\n\t\techo b\n",
+		},
+		{
+			name:  "escaped backslash does not start a continuation",
+			input: "target:\n\tprintf 'a\\\\\\\\'\n\t\techo b\n",
+			want:  "target:\n\tprintf 'a\\\\\\\\'\n\techo b\n",
+		},
+		{
+			name:  "odd run of backslashes does start a continuation",
+			input: "target:\n\tprintf 'a\\\\\\\\\\\n\t\techo b\n",
+			want:  "target:\n\tprintf 'a\\\\\\\\\\\n\t\techo b\n",
+		},
+		{
+			name:  "blank line ends the recipe and the continuation state",
+			input: "target:\n\techo a \\\n\t\techo b\n\nother:\n        echo c\n",
+			want:  "target:\n\techo a \\\n\t\techo b\n\nother:\n\techo c\n",
+		},
+		{
+			name:  "comment inside a recipe ends the continuation state",
+			input: "target:\n\techo a \\\n\t\techo b\n\t# note\n        echo c\n",
+			want:  "target:\n\techo a \\\n\t\techo b\n\t# note\n\techo c\n",
+		},
+		{
+			name:  "preserves indented heredoc bodies inside a continued command",
+			input: "target:\n\tcat <<-EOF \\\n\t\t  indented body \\\n\t\tEOF\n",
+			want:  "target:\n\tcat <<-EOF \\\n\t\t  indented body \\\n\t\tEOF\n",
+		},
+		{
+			name:  "leaves variable assignment continuations alone",
+			input: "SRCS = a.go \\\n\tb.go \\\n\tc.go\n",
+			want:  "SRCS = a.go \\\n\tb.go \\\n\tc.go\n",
+		},
+		{
+			name:  "preserves indentation on continued prerequisite lists",
+			input: "target: dep1 \\\n\t\tdep2\n\techo a\n",
+			want:  "target: dep1 \\\n\t\tdep2\n\techo a\n",
+		},
+		{
+			name:  "first recipe line after a continued prerequisite list is normalised",
+			input: "target: dep1 \\\n\t\tdep2\n        echo a\n",
+			want:  "target: dep1 \\\n\t\tdep2\n\techo a\n",
+		},
+		{
+			name:  "adds a final newline",
+			input: "target:\n\techo a \\\n\t\techo b",
+			want:  "target:\n\techo a \\\n\t\techo b\n",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, formatMakefile(tt.input))
+		})
+	}
+}
+
+func TestFormatMakefileIsIdempotent(t *testing.T) {
+	inputs := []string{
+		"target:\n\tdocker run \\\n\t\t--rm \\\n\t\timage\n",
+		"target:\n    echo a \\\n        echo b\n",
+		"SRCS = a.go \\\n\tb.go\n\nall: $(SRCS)\n\techo done\n",
+		"target:\n\tprintf 'a\\\\\\\\'\n        echo b\n",
+	}
+
+	for _, input := range inputs {
+		t.Run(input, func(t *testing.T) {
+			once := formatMakefile(input)
+			assert.Equal(t, once, formatMakefile(once))
+		})
+	}
+}
+
+func TestEndsWithContinuation(t *testing.T) {
+	tests := []struct {
+		line string
+		want bool
+	}{
+		{"echo a", false},
+		{`echo a \`, true},
+		{`echo a \\`, false},
+		{`echo a \\\`, true},
+		{`echo a \\\\`, false},
+		{`\`, true},
+		{"", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.line, func(t *testing.T) {
+			assert.Equal(t, tt.want, endsWithContinuation(tt.line))
+		})
+	}
+}

internal/handler/handler.go

@@ -870,28 +870,39 @@ func (h *Handler) Formatting(_ context.Context, params *lsp.DocumentFormattingPa
 func formatMakefile(text string) string {
 	lines := strings.Split(text, "\n")
 	inRecipe := false
+	continued := false
 
 	for i, line := range lines {
 		trimmed := strings.TrimSpace(line)
 
 		// Empty line ends recipe context.
 		if trimmed == "" {
 			inRecipe = false
+			continued = false
 			lines[i] = ""
 			continue
 		}
 
 		// Comment lines — just trim trailing whitespace.
 		if strings.HasPrefix(trimmed, "#") {
 			lines[i] = strings.TrimRight(line, " \t")
+			continued = false
 			continue
 		}
 
 		// Recipe lines — ensure tab prefix, trim trailing whitespace.
 		if inRecipe && (line[0] == '\t' || line[0] == ' ') {
-			// Normalize: ensure tab, trim trailing spaces.
-			content := strings.TrimLeft(line, " \t")
-			lines[i] = "\t" + strings.TrimRight(content, " \t")
+			if continued {
+				// Part of the previous logical line. Everything after the
+				// leading tab is passed to the shell verbatim, so preserve the
+				// author's indentation and only guarantee the tab.
+				lines[i] = "\t" + strings.TrimRight(strings.TrimPrefix(line, "\t"), " \t")
+			} else {
+				// Normalize: ensure tab, trim trailing spaces.
+				content := strings.TrimLeft(line, " \t")
+				lines[i] = "\t" + strings.TrimRight(content, " \t")
+			}
+			continued = endsWithContinuation(lines[i])
 			continue
 		}
 
@@ -904,6 +915,7 @@ func formatMakefile(text string) string {
 
 		// Trim trailing whitespace on all other lines.
 		lines[i] = strings.TrimRight(line, " \t")
+		continued = endsWithContinuation(lines[i])
 	}
 
 	result := strings.Join(lines, "\n")
@@ -921,6 +933,16 @@ func formatMakefile(text string) string {
 	return result
 }
 
+// endsWithContinuation reports whether the line ends in an unescaped backslash,
+// making the following line part of the same logical line.
+func endsWithContinuation(line string) bool {
+	backslashes := 0
+	for i := len(line) - 1; i >= 0 && line[i] == '\\'; i-- {
+		backslashes++
+	}
+	return backslashes%2 == 1
+}
+
 func isTargetLine(trimmed string) bool {
 	// A target line has a colon but no = before the colon.
 	colonIdx := strings.Index(trimmed, ":")