Fix bug where MSVC linker flags were not handled properly

Clang and GCC's `-Wl` argument can be used to pass arguments to the linker.
MSVC, however, does not recognize this option and instead uses a
/link flag at the end of all other arguments for this purpose. This commit
makes use of "/link" with MSVC when LDFLAGS are used.

Author: camio

src/run.rs

@@ -73,16 +73,16 @@ pub fn run(language: Language, program: &str) -> Result<Assert, Box<dyn Error>>
     if msvc {
         command = compiler.to_command();
 
-        command_add_compiler_flags(&mut command, &variables);
+        command_add_compiler_flags(&mut command, &variables, msvc);
         command_add_output_file(&mut command, &output_path, msvc, compiler.is_like_clang());
         command.arg(input_path.clone());
-        command.envs(variables.clone());
+        command_add_linker_flags_msvc(&mut command, &variables);
     } else {
         command = Command::new(compiler.path());
 
         command.arg(input_path.clone()); // the input must come first
         command.args(compiler.args());
-        command_add_compiler_flags(&mut command, &variables);
+        command_add_compiler_flags(&mut command, &variables, msvc);
         command_add_output_file(&mut command, &output_path, msvc, compiler.is_like_clang());
     }
 
@@ -159,31 +159,48 @@ fn command_add_output_file(command: &mut Command, output_path: &PathBuf, msvc: b
     }
 }
 
-fn command_add_compiler_flags(command: &mut Command, variables: &HashMap<String, String>) {
-    let get_env_flags = |env_name: &str| -> Vec<String> {
-        variables
-            .get(env_name)
-            .map(|e| e.to_string())
-            .ok_or_else(|| env::var(env_name))
-            .unwrap_or_default()
-            .split_ascii_whitespace()
-            .map(|slice| slice.to_string())
-            .collect()
-    };
-
-    command.args(get_env_flags("CFLAGS"));
-    command.args(get_env_flags("CPPFLAGS"));
-    command.args(get_env_flags("CXXFLAGS"));
-
-    for linker_argument in get_env_flags("LDFLAGS") {
-        command.arg(format!("-Wl,{}", linker_argument));
+fn get_env_flags(variables: &HashMap<String, String>, env_name: &str) -> Vec<String> {
+    variables
+        .get(env_name)
+        .map(|e| e.to_string())
+        .ok_or_else(|| env::var(env_name))
+        .unwrap_or_default()
+        .split_ascii_whitespace()
+        .map(|slice| slice.to_string())
+        .collect()
+}
+
+fn command_add_compiler_flags(
+    command: &mut Command,
+    variables: &HashMap<String, String>,
+    msvc: bool,
+) {
+    command.args(get_env_flags(variables, "CFLAGS"));
+    command.args(get_env_flags(variables, "CPPFLAGS"));
+    command.args(get_env_flags(variables, "CXXFLAGS"));
+
+    if !msvc {
+        for linker_argument in get_env_flags(variables, "LDFLAGS") {
+            command.arg(format!("-Wl,{}", linker_argument));
+        }
+    }
+}
+
+fn command_add_linker_flags_msvc(command: &mut Command, variables: &HashMap<String, String>) {
+    let linker_flags = get_env_flags(variables, "LDFLAGS");
+    if !linker_flags.is_empty() {
+        command.arg("/link");
+        for linker_argument in linker_flags {
+            command.arg(linker_argument);
+        }
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::predicates::*;
+    use std::env::{remove_var, set_var};
 
     #[test]
     fn test_run_c() {
@@ -203,6 +220,62 @@ mod tests {
         .success()
         .stdout(predicate::eq("Hello, World!\n").normalize());
     }
+    #[test]
+    fn test_run_c_ldflags() {
+        let host = target_lexicon::HOST.to_string();
+        let msvc = host.contains("msvc");
+        if msvc {
+            // Use a linker flag to set the stack size and run a program that
+            // outputs its stack size. If the linker flags aren't set
+            // properly, the program will output the wrong value.
+
+            set_var("INLINE_C_RS_LDFLAGS", "/STACK:0x40000");
+            run(
+                Language::C,
+                r#"
+                #include <Windows.h>
+
+                #include <stdio.h>
+
+                int main() {
+                    ULONG_PTR stack_low_limit, stack_high_limit;
+                    GetCurrentThreadStackLimits(&stack_low_limit, &stack_high_limit);
+                    printf("%#llx", stack_high_limit-stack_low_limit);
+
+                    return 0;
+                }
+            "#,
+            )
+            .unwrap()
+            .success()
+            .stdout(predicate::eq("0x40000").normalize());
+
+            remove_var("INLINE_C_RS_LDFLAGS");
+        } else {
+            // Introduces a symbol using linker flags and builds a program that
+            // ODR uses that symbol. If the linker flags aren't set properly,
+            // there will be a linker error.
+
+            set_var("INLINE_C_RS_LDFLAGS", "--defsym MY_SYMBOL=0x0");
+            run(
+                Language::C,
+                r#"
+                #include <stdio.h>
+
+                extern void* MY_SYMBOL;
+
+                int main() {
+                    printf("%p", MY_SYMBOL);
+                    return 0;
+                }
+            "#,
+            )
+            .unwrap()
+            .success();
+
+            remove_var("INLINE_C_RS_LDFLAGS");
+        }
+    }
 
     #[test]
     fn test_run_cxx() {