Shasta extension for libbash

dash-bash-diffs.md

@@ -0,0 +1,36 @@
+# Differences between Dash and Bash frontends
+
+Shasta was designed for libdash, with libbash support added later.
+Both `json_to_ast` (for libdash) and `bash_to_shasta_ast` (for libbash) contain `to_ast_node(s)` functions,
+which each take a parsed, untyped AST and convert it to a shasta AST as defined in `ast_node`.
+Thr transformation is direct; bash is assumed to be a subset of dash. This is not strictly true, since
+both have some minor divergences from the POSIX spec, but is good enough.
+
+### The following fields of `AstNodes` are only used for Bash scripts:
+
+- `RedirectionNode` and `*RedirNode`: The `fd` field is either `('var', filename)` or `('fixed', fd)`.
+   Dash only uses the latter form; the first exists to support bashisms like `exec {fd} > log.txt`,
+   which open the file and assigns `fd` the new file descriptor.
+- `FileRedirNode`: 'ReadingString' subtype. Handles here-strings.
+- `BackgroundNode`: The `after_ampersand` field. Handles an edge case with heredocs.
+
+The pretty printer uses the various `nobraces` and `semicolon` fields to determine
+whether braces and semicolons are printed. In dash, this doesn't matter, but in bash
+they can lead to a syntax error. For example:
+
+```bash
+( { echo hi; echo bye } )
+```
+
+is invalid.
+
+### The following AstNodes are only used for Bash scripts:
+
+- `SelectNode`
+- `ArithNode`
+- `CondNode`
+- `ArithForNode`
+- `CoprocNode`
+- `TimeNode`
+- `SingleArgRedirNode`
+- `GroupNode`

pyproject.toml

@@ -14,6 +14,7 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Operating System :: POSIX",
 ]
+dependencies = ["libbash"]
 
 [project.urls]
 "Homepage" = "https://github.com/binpash/shasta"