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Dafny string literals with surrogate characters compiled to invalid Go strings #1980

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robin-aws opened this issue Apr 6, 2022 · 2 comments · Fixed by #2926
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Dafny string literals with surrogate characters compiled to invalid Go strings #1980

robin-aws opened this issue Apr 6, 2022 · 2 comments · Fixed by #2926
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kind: bug Crashes, unsoundness, incorrect output, etc. If possible, add a `part:` label lang: golang Dafny's transpiler to Go and its runtime part: code-generation Support for transpiling Dafny to another language. If relevant, add a `lang:` tag

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@robin-aws
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Dafny string literals are translated literally to Go literals, but \uXXXX in Dafny is interpreted as a UTF-16 code point, whereas Go will interpret the same escape sequences as Unicode scalar values, which excludes surrogates.

method Foo() {
  // Mathematical Sans-Serif Bold Italic Small Psi - represented as a surrogate of U+1D7C1
  var s := "\uD835\uDFC1";
}
$ dafny /compile:3 /compileTarget:go src/Scratch.dfy 

Dafny program verifier finished with 0 verified, 0 errors
Wrote textual form of target program to Scratch-go/src/Scratch.go
Additional target code written to Scratch-go/src/dafny/dafny.go
Additional target code written to Scratch-go/src/System_/System_.go
# command-line-arguments
src/Scratch-go/src/Scratch.go:46:37: escape is invalid Unicode code point U+D835
src/Scratch-go/src/Scratch.go:46:43: escape is invalid Unicode code point U+DFC1
@robin-aws robin-aws added kind: bug Crashes, unsoundness, incorrect output, etc. If possible, add a `part:` label part: code-generation Support for transpiling Dafny to another language. If relevant, add a `lang:` tag lang: golang Dafny's transpiler to Go and its runtime labels Apr 6, 2022
@robin-aws
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See also #413

@robin-aws robin-aws self-assigned this Jul 8, 2022
@robin-aws robin-aws mentioned this issue Sep 27, 2022
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@robin-aws
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Note that this really depends on the proper, deeper fix proposed in dafny-lang/rfcs#13, because another case is a string with invalid uses of surrogate characters that cannot be losslessly expressed as a Go string.

This was referenced Oct 25, 2022
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robin-aws added a commit that referenced this issue Nov 3, 2022
@robin-aws @cpitclaudel
fix: Handle UTF-16 escapes and invalid surrogate sequences in Python …
c81c3ca 
…and Go (#2926)

Fixes #1980. Fixes #2925.

Should fix the root cause of #2934, but I'm not claiming the complete
fix, as attempting to include unescaped, non-ASCII characters in a Dafny
source file is revealing platform-specific headaches in the integration
test runner I'd like to address in a separate PR.

Printing non-ASCII characters, especially invalid UTF-16 sequences, is
still inconsistent across backends, but at least should not crash after
this change. Again this is difficult to test effectively across
platforms in our testing architecture.

<small>By submitting this pull request, I confirm that my contribution
is made under the terms of the [MIT
license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>

Co-authored-by: Clément Pit-Claudel <[email protected]>
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fix: Handle UTF-16 escapes and invalid surrogate sequences in Python and Go robin-aws/dafny
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