LibPDF: Allow and skip comments in PostScriptCalculatorFunction

The PDF spec doesn't explicitly mention supporting comments here, but other implementations (I checked Preview.app and PDFium) seem to allow and skip them, so follow suit.
SerenityOS · Feb 25, 2025 · 137fc03 · 137fc03
1 parent 4f74c82
commit 137fc03
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Showing 2 changed files with 61 additions and 4 deletions.
diff --git a/Tests/LibPDF/TestPDF.cpp b/Tests/LibPDF/TestPDF.cpp
@@ -312,6 +312,42 @@ TEST_CASE(postscript)
     check_evaluate("{ pop }"sv, { 8.0f, 1.0f, 0.5f }, { 8.0f, 1.0f });
     check_evaluate("{ 3 1 roll }"sv, { 0.5f, 1.0f, 2.0f }, { 2.0f, 0.5f, 1.0f });
     check_evaluate("{ 3 -1 roll }"sv, { 0.5f, 1.0f, 2.0f }, { 1.0f, 2.0f, 0.5f });
+
+    // Comments
+    check_evaluate(R"(
+    % comment
+    {
+        % comment
+        1
+
+        % comment
+        {
+            % comment
+            1
+            % comment
+        }
+        % comment
+        if
+
+        % comment
+        {
+            % comment
+            1
+            % comment
+        }
+        % comment
+        {
+            % comment
+            0
+            % comment
+        }
+        ifelse
+
+        % comment
+    }
+    % comment
+    )"sv,
+        {}, { 1.0f });
 }
 
 TEST_CASE(render)

diff --git a/Userland/Libraries/LibPDF/Function.cpp b/Userland/Libraries/LibPDF/Function.cpp
@@ -512,6 +512,7 @@ class PostScriptCalculatorFunction final : public Function {
         Vector<Token> if_false;
     };
 
+    static bool skip_whitespace_and_comments(Reader&);
     static PDFErrorOr<Vector<Token>> parse_postscript_calculator_function(Reader&, Vector<NonnullOwnPtr<IfElse>>&);
 
     struct Stack {
@@ -639,22 +640,42 @@ Optional<PostScriptCalculatorFunction::OperatorType> PostScriptCalculatorFunctio
     return {};
 }
 
+bool PostScriptCalculatorFunction::skip_whitespace_and_comments(Reader& reader)
+{
+    bool did_skip = false;
+    while (!reader.done()) {
+        if (reader.consume_whitespace()) {
+            did_skip = true;
+            continue;
+        }
+        if (reader.matches('%')) {
+            did_skip = true;
+            reader.consume();
+            while (!reader.consume_eol())
+                reader.consume();
+            continue;
+        }
+        break;
+    }
+    return did_skip;
+}
+
 PDFErrorOr<Vector<PostScriptCalculatorFunction::Token>>
 PostScriptCalculatorFunction::parse_postscript_calculator_function(Reader& reader, Vector<NonnullOwnPtr<IfElse>>& if_elses)
 {
     // Assumes valid syntax.
-    reader.consume_whitespace();
+    skip_whitespace_and_comments(reader);
     if (!reader.consume('{'))
         return Error { Error::Type::MalformedPDF, "PostScript expected '{'" };
 
     Vector<PostScriptCalculatorFunction::Token> tokens;
     while (!reader.matches('}')) {
-        if (reader.consume_whitespace())
+        if (skip_whitespace_and_comments(reader))
             continue;
 
         if (reader.matches('{')) {
             auto if_true = TRY(parse_postscript_calculator_function(reader, if_elses));
-            reader.consume_whitespace();
+            skip_whitespace_and_comments(reader);
             if (reader.matches("if")) {
                 reader.consume(2);
                 tokens.append({ OperatorType::If, (int)if_elses.size() });
@@ -664,7 +685,7 @@ PostScriptCalculatorFunction::parse_postscript_calculator_function(Reader& reade
 
             VERIFY(reader.matches('{'));
             auto if_false = TRY(parse_postscript_calculator_function(reader, if_elses));
-            reader.consume_whitespace();
+            skip_whitespace_and_comments(reader);
 
             if (reader.matches("ifelse")) {
                 reader.consume(6);