Stop throwing NPE on Type3 char proc metrics when no glyph bbox is declared

[bundolee]

Problem

Type3CharProcParser.getAscent() and getDescent() return primitive double, but the backing ascent / descent fields are Double and legitimately stay null.

A char proc whose first operator is d0 specifies the glyph width only (ISO 32000-1, 9.6.5.3) and declares no glyph bounding box, so parse() returns early with both fields unset:

nextToken();
if (getToken().type == Token.Type.TT_KEYWORD && getToken().getValue().equals(D0)) {
    return;                     // ascent / descent stay null
}

Reading either metric for such a glyph throws NullPointerException while unboxing:

java.lang.NullPointerException: Cannot invoke "java.lang.Double.doubleValue()" because "this.ascent" is null
	at org.verapdf.pd.font.type3.Type3CharProcParser.getAscent(Type3CharProcParser.java:96)
	at org.verapdf.pd.font.type3.PDType3Font.getAscentFromProgram(PDType3Font.java:166)

A single d0 glyph anywhere in a Type 3 font is enough to trigger it.

Fix

Both getters shipped in v1.31.48, so their descriptors are left alone to stay binary compatible:

Method	Behaviour
double getAscent() / double getDescent()	Unchanged signature. Substitute 0 for an undefined metric instead of throwing. Deprecated.
Double getAscentOrNull() / Double getDescentOrNull()	New. Distinguish "no glyph bounding box" from a real 0.

PDType3Font.getAscentFromProgram / getDescentFromProgram now read the nullable accessors. Without that the unboxing NPE would simply move up one frame — those methods are declared Double and already return null when the char proc cannot be parsed.

The consumer in wcag-validation ChunkParser already guards with if (glyphAscent != null) before aggregating, so no change is needed there.

Why the nullable accessors matter

0 keeps the deprecated path running, but it is not a correct metric. Ascent and descent are aggregated by maximum and minimum across the glyphs of a font, so a 0 descent wins the minimum comparison against the real negative descents of the surrounding glyphs and silently flattens the text line box — a quality regression that is harder to notice than a crash. d0 genuinely means "no bounding box", so null is the accurate value for callers that can handle it.

Deriving a substitute from /FontDescriptor or /FontBBox was considered and rejected: it invents information the char proc does not declare, and the affected documents are exactly the ones whose font metadata is unreliable.

Tests

Adds Type3CharProcParserTest:

Case	Expectation
d1 char proc	width, ascent and descent all reported
d0 char proc	width reported, nullable accessors return null
d0 and d1 via deprecated getters	0 for undefined, real value otherwise; never throws
bbox not terminated by d1	IOException, metrics cleared

The d0 case reproduces the NullPointerException against the original getters (verified by reverting: 2 errors) and passes with this change.

Full module suite: 375 tests, 0 failures, 0 errors.

Summary by CodeRabbit

• Bug Fixes

  • Corrected Type 3 font metric handling when character procedures define width without a bounding box.
  • Preserved undefined ascent and descent values instead of treating them as valid zero metrics.
  • Improved handling of malformed character procedures by clearing invalid metrics after parsing errors.

• API Updates

  • Added nullable accessors for ascent and descent metrics.
  • Deprecated legacy metric accessors, which now return zero when values are undefined.

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Reviewing files that changed from the base of the PR and between 27afc43 and 3b4ebbe.

📒 Files selected for processing (3)

• src/main/java/org/verapdf/pd/font/type3/PDType3Font.java
• src/main/java/org/verapdf/pd/font/type3/Type3CharProcParser.java
• src/test/java/org/verapdf/pd/font/type3/Type3CharProcParserTest.java

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📝 Walkthrough

Walkthrough

Type3CharProcParser now distinguishes undefined ascent and descent from zero for d0 procedures. PDType3Font uses nullable metrics, and tests cover d0, d1, and corrupted procedures.

Changes

Type3 character metrics

Layer / File(s)	Summary
Nullable metrics and parser validation src/main/java/org/verapdf/pd/font/type3/Type3CharProcParser.java, src/test/java/org/verapdf/pd/font/type3/Type3CharProcParserTest.java	The parser adds nullable ascent and descent getters. Deprecated primitive getters return 0 for undefined metrics. Tests validate d0, d1, and parse-error behavior.
Font metric integration src/main/java/org/verapdf/pd/font/type3/PDType3Font.java	Font metric extraction now uses nullable ascent and descent getters.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 3b4eb

The fix prevents crashes for Type 3 glyphs without bounding boxes while preserving accurate undefined metrics for callers that support them. No actionable merge-blocking risk remains after normal checks and review.

Suggested reviewers: lonelymidoriya

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: preventing NullPointerException failures for Type3 character procedures without a declared glyph bounding box.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@src/main/java/org/verapdf/pd/font/type3/Type3CharProcParser.java`:
- Line 101: Restore primitive double return types for getAscent() and
getDescent() in Type3CharProcParser to preserve the existing JVM method
descriptors; if nullable values must remain supported, expose them through
separate methods, or explicitly classify this change as a breaking API release.

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ℹ️ Review info

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📒 Files selected for processing (2)

• src/main/java/org/verapdf/pd/font/type3/Type3CharProcParser.java
• src/test/java/org/verapdf/pd/font/type3/Type3CharProcParserTest.java

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