Add --preserve-unused-functions

to keep otherwise pruned static / inline functions.

Closes: immunant#287

Author: chrysn

c2rust-transpile/src/c_ast/mod.rs

@@ -519,7 +519,7 @@ impl TypedAstContext {
         }
     }
 
-    pub fn prune_unused_decls(&mut self) {
+    pub fn prune_unused_decls(&mut self, preserve_unused_functions: bool) {
         // Starting from a set of root declarations, walk each one to find declarations it
         // depends on. Then walk each of those, recursively.
 
@@ -545,6 +545,13 @@ impl TypedAstContext {
                     to_walk.push(decl_id);
                     used.insert(decl_id);
                 }
+                CDeclKind::Function {
+                    body: Some(_),
+                    ..
+                } if preserve_unused_functions => {
+                    to_walk.push(decl_id);
+                    used.insert(decl_id);
+                }
                 CDeclKind::Variable {
                     is_defn: true,
                     is_externally_visible: true,

c2rust-transpile/src/lib.rs

@@ -109,6 +109,7 @@ pub struct TranspilerConfig {
     pub translate_const_macros: bool,
     pub translate_fn_macros: bool,
     pub disable_refactoring: bool,
+    pub preserve_unused_functions: bool,
     pub log_level: log::LevelFilter,
 
     // Options that control build files

c2rust-transpile/src/translator/mod.rs

@@ -530,7 +530,7 @@ pub fn translate(
 
         // Headers often pull in declarations that are unused;
         // we simplify the translator output by omitting those.
-        t.ast_context.prune_unused_decls();
+        t.ast_context.prune_unused_decls(tcfg.preserve_unused_functions);
 
         enum Name<'a> {
             VarName(&'a str),

c2rust/src/bin/c2rust-transpile.rs

@@ -89,6 +89,7 @@ fn main() {
         translate_const_macros: matches.is_present("translate-const-macros"),
         translate_fn_macros: matches.is_present("translate-fn-macros"),
         disable_refactoring: matches.is_present("disable-refactoring"),
+        preserve_unused_functions: matches.is_present("preserve-unused-functions"),
 
         use_c_loop_info: !matches.is_present("ignore-c-loop-info"),
         use_c_multiple_info: !matches.is_present("ignore-c-multiple-info"),

c2rust/src/transpile.yaml

@@ -172,6 +172,10 @@ args:
       long: disable-refactoring
       help: Disable running refactoring tool after translation
       takes_value: false
+  - preserve-unused-functions:
+      long: preserve-unused-functions
+      help: Include static and inline functions in translation
+      takes_value: false
   - log-level:
       long: log-level
       help: Logging level