Do not write to code file if header is missing

8 files changed, 167 insertions, 86 deletions

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/CodeWriter.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/CodeWriter.java
index a0b9005..81fd091 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/CodeWriter.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/CodeWriter.java
@@ -18,6 +18,7 @@ public class CodeWriter implements AutoCloseable {
     public static class InMemoryCodeWriterFile implements CodeWriterFile {
         private final Optional<String> originalContents;
         private final StringWriter stringWriter;
+        private boolean writerOpened;
 
         public InMemoryCodeWriterFile(
             Optional<String> originalContents,
@@ -25,6 +26,7 @@ public class CodeWriter implements AutoCloseable {
         ) {
             this.originalContents = originalContents;
             this.stringWriter = stringWriter;
+            this.writerOpened = false;
         }
 
         @Override
@@ -38,8 +40,13 @@ public class CodeWriter implements AutoCloseable {
 
         @Override
         public Writer openWriter() throws IOException {
+            this.writerOpened = true;
             return stringWriter;
         }
+
+        public boolean isWriterOpened() {
+            return writerOpened;
+        }
     }
 
     public record CustomAreas(
@@ -90,11 +97,16 @@ public class CodeWriter implements AutoCloseable {
         }
     }
 
-    public static CodeWriter file(
+    public interface Write {
+        void write(CodeWriter writer) throws IOException;
+    }
+
+    public static void writeTo(
         Path path,
-        String lineCommentStart
+        String lineCommentStart,
+        Write write
     ) throws IOException {
-        return file(
+        writeTo(
             new CodeWriterFile() {
                 @Override
                 public String readString() throws IOException {
@@ -107,20 +119,31 @@ public class CodeWriter implements AutoCloseable {
                     return new FileWriter(path.toFile());
                 }
             },
-            lineCommentStart
+            lineCommentStart,
+            write
         );
     }
 
-    public static CodeWriter file(
+    public static void writeTo(
         CodeWriterFile file,
-        String lineCommentStart
+        String lineCommentStart,
+        Write write
     ) throws IOException {
+        var originalContents = readFile(file);
+
+        var header = lineCommentStart + " Generated by hobgoblin.\n\n";
+        if (originalContents.isPresent() && !originalContents.get().startsWith(header)) {
+            return;
+        }
+
         var customAreaStart = lineCommentStart + " Custom area start: ";
         var customAreaEnd = lineCommentStart + " Custom area end: ";
+
         var customAreas = readCustomAreas(file, customAreaStart, customAreaEnd);
-        var writer = file.openWriter();
-        // TODO: warn if custom areas are unused?
-        return new CodeWriter(writer, lineCommentStart, customAreas);
+        try (var writer = file.openWriter()) {
+            // TODO: warn if custom areas are unused?
+            write.write(new CodeWriter(writer, header, customAreas));
+        }
     }
 
     private static CustomAreas readCustomAreas(
@@ -136,23 +159,30 @@ public class CodeWriter implements AutoCloseable {
         }
     }
 
+    private static Optional<String> readFile(CodeWriterFile file) throws IOException {
+        try {
+            return Optional.of(file.readString());
+        } catch (NoSuchFileException exception) {
+            return Optional.empty();
+        }
+    }
+
     private final Writer writer;
-    private final String lineCommentStart;
+    private final String header;
     private final CustomAreas customAreas;
     private int indent;
     private boolean pendingIndent;
 
-    public CodeWriter(Writer writer, String lineCommentStart, CustomAreas customAreas) {
+    public CodeWriter(Writer writer, String header, CustomAreas customAreas) {
         this.writer = writer;
-        this.lineCommentStart = lineCommentStart;
+        this.header = header;
         this.customAreas = customAreas;
         this.indent = 0;
         this.pendingIndent = false;
     }
 
     public void writeHeader() throws IOException {
-        writer.write(lineCommentStart);
-        writer.write(" Generated by hobgoblin.\n\n");
+        writer.write(header);
     }
 
     public void write(String value) throws IOException {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
index 1325149..d7f4bb0 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/java/JavaGenerator.java
@@ -29,9 +29,11 @@ public class JavaGenerator {
             var javaCompilationUnitPath = sourceRootDirectory
                 .resolve(javaCompilationUnit.packageName().parts().stream().map(JavaIdentifier::value).collect(Collectors.joining(File.separator)))
                 .resolve(javaCompilationUnit.typeDeclaration().name().value() + ".java");
-            try (var writer = JavaWriter.file(javaCompilationUnitPath)) {
-                writer.writeCompilationUnit(javaCompilationUnit);
-            }
+
+            JavaWriter.writeTo(
+                javaCompilationUnitPath,
+                writer -> writer.writeCompilationUnit(javaCompilationUnit)
+            );
         }
     }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rust/RustGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rust/RustGenerator.java
index 0a0290d..22b6d7d 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rust/RustGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rust/RustGenerator.java
@@ -27,9 +27,9 @@ public class RustGenerator {
                 .map(name -> name.value())
                 .collect(Collectors.joining(File.separator)) + ".rs"
         );
-        try (var writer = RustWriter.file(path)) {
+        RustWriter.writeTo(path, writer -> {
             writer.writeModule(rustModule);
-        }
+        });
     }
 
     public RustPath generateRustTypeExpression(Type type) {
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
index b593364..7af7e01 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriter.java
@@ -15,18 +15,24 @@ import static org.zwobble.hobgoblin.compiler.output.CodeWriter.writeWithSeparato
 public class JavaWriter implements AutoCloseable {
     private static final String LINE_COMMENT_START = "//";
 
-    public static JavaWriter file(CodeWriter.CodeWriterFile file) throws IOException {
-        return new JavaWriter(CodeWriter.file(
-            file,
-            LINE_COMMENT_START
-        ));
+    public interface Write {
+        void write(JavaWriter writer) throws IOException;
     }
 
-    public static JavaWriter file(Path path) throws IOException {
-        return new JavaWriter(CodeWriter.file(
+    public static void writeTo(Path path, Write write) throws IOException {
+        CodeWriter.writeTo(
             path,
-            LINE_COMMENT_START
-        ));
+            LINE_COMMENT_START,
+            writer -> write.write(new JavaWriter(writer))
+        );
+    }
+
+    public static void writeTo(CodeWriter.CodeWriterFile file, Write write) throws IOException {
+        CodeWriter.writeTo(
+            file,
+            LINE_COMMENT_START,
+            writer -> write.write(new JavaWriter(writer))
+        );
     }
 
     private final CodeWriter writer;
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
index 2d7e9ed..d0552ad 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
@@ -15,18 +15,24 @@ import static org.zwobble.hobgoblin.compiler.output.CodeWriter.writeWithSeparato
 public class RustWriter implements AutoCloseable {
     private static final String LINE_COMMENT_START = "//";
 
-    public static RustWriter file(CodeWriter.CodeWriterFile file) throws IOException {
-        return new RustWriter(CodeWriter.file(
-            file,
-            LINE_COMMENT_START
-        ));
+    public interface Write {
+        void write(RustWriter writer) throws IOException;
     }
 
-    public static RustWriter file(Path path) throws IOException {
-        return new RustWriter(CodeWriter.file(
+    public static void writeTo(Path path, Write write) throws IOException {
+        CodeWriter.writeTo(
             path,
-            LINE_COMMENT_START
-        ));
+            LINE_COMMENT_START,
+            writer -> write.write(new RustWriter(writer))
+        );
+    }
+
+    public static void writeTo(CodeWriter.CodeWriterFile file, Write write) throws IOException {
+        CodeWriter.writeTo(
+            file,
+            LINE_COMMENT_START,
+            writer -> write.write(new RustWriter(writer))
+        );
     }
 
     private final CodeWriter writer;
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java
index b0ff40c..2b3ad6d 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java
@@ -14,17 +14,21 @@ public class CodeWriterTests {
     @Test
     public void whenFileDoesNotExistThenCustomAreasAreEmpty() throws IOException {
         var stringWriter = new StringWriter();
-        var codeWriter = CodeWriter.file(
-            new CodeWriter.InMemoryCodeWriterFile(Optional.empty(), stringWriter),
-            "//"
+        var file = new CodeWriter.InMemoryCodeWriterFile(Optional.empty(), stringWriter);
+
+        CodeWriter.writeTo(
+            file,
+            "//",
+            codeWriter -> {
+                codeWriter.writeHeader();
+                codeWriter.write("Before");
+                codeWriter.newLine();
+                codeWriter.writeCustomArea("body");
+                codeWriter.write("After");
+                codeWriter.newLine();
+            }
         );
 
-        codeWriter.writeHeader();
-        codeWriter.write("Before");
-        codeWriter.newLine();
-        codeWriter.writeCustomArea("body");
-        codeWriter.write("After");
-        codeWriter.newLine();
 
         assertThat(stringWriter.toString(), equalTo("""
             // Generated by hobgoblin.
@@ -39,21 +43,28 @@ public class CodeWriterTests {
     @Test
     public void whenExistingFileIsMissingCustomAreaThenCustomAreaIsEmpty() throws IOException {
         var stringWriter = new StringWriter();
-        var codeWriter = CodeWriter.file(
-            new CodeWriter.InMemoryCodeWriterFile(Optional.of(""), stringWriter),
-            "//"
-        );
+        var originalContents = """
+            // Generated by hobgoblin.
 
-        codeWriter.writeHeader();
-        codeWriter.write("Before");
-        codeWriter.newLine();
-        codeWriter.writeCustomArea("body");
-        codeWriter.write("After");
-        codeWriter.newLine();
+            """;
+        var file = new CodeWriter.InMemoryCodeWriterFile(Optional.of(originalContents), stringWriter);
+
+        CodeWriter.writeTo(
+            file,
+            "//",
+            codeWriter -> {
+                codeWriter.writeHeader();
+                codeWriter.write("Before");
+                codeWriter.newLine();
+                codeWriter.writeCustomArea("body");
+                codeWriter.write("After");
+                codeWriter.newLine();
+            }
+        );
 
         assertThat(stringWriter.toString(), equalTo("""
             // Generated by hobgoblin.
-            
+
             Before
             // Custom area start: body
             // Custom area end: body
@@ -65,6 +76,8 @@ public class CodeWriterTests {
     public void whenExistingFileHasCustomAreasThenCustomAreaContentsArePreserved() throws IOException {
         var stringWriter = new StringWriter();
         var originalContents = """
+            // Generated by hobgoblin.
+
             // Custom area start: head
             Custom head.
             // Custom area end: head
@@ -72,18 +85,21 @@ public class CodeWriterTests {
             Custom body.
             // Custom area end: body
             """;
-        var codeWriter = CodeWriter.file(
-            new CodeWriter.InMemoryCodeWriterFile(Optional.of(originalContents), stringWriter),
-            "//"
-        );
+        var file = new CodeWriter.InMemoryCodeWriterFile(Optional.of(originalContents), stringWriter);
 
-        codeWriter.writeHeader();
-        codeWriter.writeCustomArea("head");
-        codeWriter.writeCustomArea("body");
+        CodeWriter.writeTo(
+            file,
+            "//",
+            codeWriter -> {
+                codeWriter.writeHeader();
+                codeWriter.writeCustomArea("head");
+                codeWriter.writeCustomArea("body");
+            }
+        );
 
         assertThat(stringWriter.toString(), equalTo("""
             // Generated by hobgoblin.
-            
+
             // Custom area start: head
             Custom head.
             // Custom area end: head
@@ -92,4 +108,31 @@ public class CodeWriterTests {
             // Custom area end: body
             """));
     }
+
+    @Test
+    public void whenExistingFileIsMissingHeaderThenNothingIsWritten() throws IOException {
+        var stringWriter = new StringWriter();
+        var originalContents = """
+            // Custom area start: head
+            Custom head.
+            // Custom area end: head
+            // Custom area start: body
+            Custom body.
+            // Custom area end: body
+            """;
+        var file = new CodeWriter.InMemoryCodeWriterFile(Optional.of(originalContents), stringWriter);
+
+        CodeWriter.writeTo(
+            file,
+            "//",
+            codeWriter -> {
+                codeWriter.writeHeader();
+                codeWriter.writeCustomArea("head");
+                codeWriter.writeCustomArea("body");
+            }
+        );
+
+        assertThat(stringWriter.toString(), equalTo(""));
+        assertThat(file.isWriterOpened(), equalTo(false));
+    }
 }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
index 2889032..9b16328 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/java/JavaWriterTests.java
@@ -1698,7 +1698,9 @@ public class JavaWriterTests {
         var string = write(
             writer -> writer.writeTypeDeclaration(java),
             """
-                public class Point {
+            // Generated by hobgoblin.
+
+            public class Point {
                 // Custom area start: Point body
                 // <custom area>
                 // Custom area end: Point body
@@ -1717,24 +1719,20 @@ public class JavaWriterTests {
 
     // == Doc comments ==
 
-    private String write(Write write) throws IOException {
+    private String write(JavaWriter.Write write) throws IOException {
         return write(write, Optional.empty());
     }
 
-    private String write(Write write, String originalContents) throws IOException {
+    private String write(JavaWriter.Write write, String originalContents) throws IOException {
         return write(write, Optional.of(originalContents));
     }
 
-    private String write(Write write, Optional<String> originalContents) throws IOException {
+    private String write(JavaWriter.Write write, Optional<String> originalContents) throws IOException {
         var stringWriter = new StringWriter();
-        var javaWriter = JavaWriter.file(
-            new CodeWriter.InMemoryCodeWriterFile(originalContents, stringWriter)
+        JavaWriter.writeTo(
+            new CodeWriter.InMemoryCodeWriterFile(originalContents, stringWriter),
+            write
         );
-        write.write(javaWriter);
         return stringWriter.toString();
     }
-
-    private interface Write {
-        void write(JavaWriter writer) throws IOException;
-    }
 }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
index e9edb72..4a81031 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
@@ -1204,24 +1204,20 @@ public class RustWriterTests {
         assertThat(string, equalTo("r#const"));
     }
 
-    private String write(Write write) throws IOException {
+    private String write(RustWriter.Write write) throws IOException {
         return write(write, Optional.empty());
     }
 
-    private String write(Write write, String originalContents) throws IOException {
+    private String write(RustWriter.Write write, String originalContents) throws IOException {
         return write(write, Optional.of(originalContents));
     }
 
-    private String write(Write write, Optional<String> originalContents) throws IOException {
+    private String write(RustWriter.Write write, Optional<String> originalContents) throws IOException {
         var stringWriter = new StringWriter();
-        var rustWriter = RustWriter.file(
-            new CodeWriter.InMemoryCodeWriterFile(originalContents, stringWriter)
+        RustWriter.writeTo(
+            new CodeWriter.InMemoryCodeWriterFile(originalContents, stringWriter),
+            write
         );
-        write.write(rustWriter);
         return stringWriter.toString();
     }
-
-    private interface Write {
-        void write(RustWriter writer) throws IOException;
-    }
 }