[PR] Pdfbox 6251 usecmap cidrange precedence [pdfbox]

["pcorless (via GitHub)" <gi...@apache.org>]

pcorless opened a new pull request, #515:
URL: https://github.com/apache/pdfbox/pull/515

   # PDFBOX-6251: a CMap's own cid mappings lose to the ones it inherits via usecmap
   
   A CMap that starts with `usecmap` may redefine any code it inherits. It currently can't:
   `useCmap` merges the parent's `cidchar`/`cidrange` mappings into the same collections as the
   importing CMap's own, and since `usecmap` is read from the header, the parent's land in
   `codeToCid`/`codeToCidRanges` first. `toCID` scans the range list first-match, so an inherited
   range that covers a code beats the mapping the CMap declared for it.
   
   ```java
   new CMapParser().parsePredefined("ETenms-B5-H").toCID(0x41, 1);  // 13681, should be 34
   ```
   
   `ETenms-B5-H` exists only to do this override: it uses `ETen-B5-H`, then remaps 0x20-0x7E to the
   proportional latin CIDs 1-95 where the parent has the fullwidth forms at 13648+. Its parsed ranges
   hold both, inherited first:
   
   ```
   [0]   32..126 -> 13648   (from ETen-B5-H, always matches first)
   [226] 32..126 -> 1       (its own, never reached)
   ```
   
   **Scope:** 31 of the 92 bundled CMaps declare mappings of their own on top of a `usecmap`, and all
   31 are affected. Two are horizontal (`ETenms-B5-H`, `UniJIS-UCS2-HW-H`); the other 29 are `-V`
   variants whose own mappings select the vertical forms, so vertical CJK gets horizontal glyphs.
   
   **Symptom:** the wrong glyph, and usually the wrong width with it — `/W` is indexed by CID, so a
   wrong CID falls outside the array and the advance drops to `/DW` = 1000. Latin text renders as
   `J a v a S e r v e r`.
   
   ## Fix
   
   Inherited mappings move to `inheritedCodeToCid`/`inheritedCodeToCidRanges`, consulted only after
   the CMap's own: own map -> own ranges -> inherited map -> inherited ranges.
   
   A `usecmap` chain stays nearest-wins, which needs opposite insertion orders: the maps are keyed, so
   `putAll` is last-wins (deepest first, nearer on top); the range list is first-match, so the nearer
   CMap's ranges go in ahead.
   
   Three things fell out of it:
   
   - **`hasCIDMappings` has to count inherited mappings.** `Identity-V` declares none of its own, so
     once the inherited ones move it would report false and `toCID` would return 0 for every code.
   - **The maps are copied, not shared.** This kills a latent aliasing bug: the old
     `codeToCid.putIfAbsent(length, mappings)` stored the parent's inner map *by reference* when the
     importing CMap had no mapping of that length yet, so a later `addCIDMapping` wrote into the
     cached predefined parent and corrupted it for everyone after.
   - **CID 0 is a mapping, not a miss.** The private range scan returned 0 for both, which with two
     range lists would send a CMap's own `cidrange` to CID 0 through to the inherited mappings. It
     now returns -1 for "no range covers this"; public `toCID` still returns 0.
   
   ## Tests
   
   Seven added to `TestCMapParser`, `mvn -pl fontbox -am test` green (214):
   
   | Test | Covers |
   |---|---|
   | `testUseCmapOwnMappingsWin` | the case above, both `toCID` overloads |
   | `testUseCmapChainKeepsNearestMapping` | a two-level chain stays nearest-wins |
   | `testUseCmapOwnMappingsBeatInheritedRanges` | own cidchar and cidrange beat an inherited range |
   | `testUseCmapOnlyInheritedMappings` | `Identity-V`, everything inherited |
   | `testUseCmapDoesNotShareMappingsWithTheUsedCMap` | the used CMap isn't mutated |
   | `testUseCmapOwnRangeBeatsInheritedChar` | own cidrange beats an inherited cidchar |
   | `testUseCmapOwnMappingToCidZeroIsNotAFallthrough` | CID 0 is a mapping, not a miss |
   


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Re: [PR] PDFBOX-6251 usecmap cidrange precedence [pdfbox]

["asf-gitbox-commits (via GitHub)" <gi...@apache.org>]

asf-gitbox-commits closed pull request #515: PDFBOX-6251 usecmap cidrange precedence
URL: https://github.com/apache/pdfbox/pull/515


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