顯式將環境狀態附加到SCons生成器依賴項MD5指紋

Question

我修改了我的SCons Builder操作使用subprocess.Popen()而不是env.Execute()。但我仍然需要對env的內容添加一些md5-sum依賴項檢查，以便重建和緩存新的目標文件。我如何附加到SCons內部MD5哈希？

Answer 1

假設你有一個使用環境變量建設者：

# Just an example. The point is that the output of this function 
# depends upon an environment variable 
def bld_func(target, source, env): 
    with open(str(target[0]), 'w') as f: 
     f.write(' '.join(str(t) for t in target) + '\n') 
     f.write(' '.join(str(s) for s in source) + '\n') 
     f.write(env.subst('$MY_VAR') + '\n') 
bld = Builder(action=bld_func) 

和調用SConstruct它：

env = Environment() 
env['BUILDERS']['BLD'] = bld 
env.BLD('output.txt', 'input.txt', MY_VAR=ARGUMENTS['MY_VAR']) 

此構建不會，如果你更改值重新執行MY_VAR的：

$ scons -Q MY_VAR=cc output.txt 
bld_func(["output.txt"], ["input.txt"]) 
$ scons -Q MY_VAR=gcc output.txt 
scons: `output.txt' is up to date. 

但是，你可以添加一個字符串與值的依賴：

env.Depends('output.txt', env.Value(env.subst('$MY_VAR'))) 

邏輯的地方把這樣的關係在一個發射器：

def bld_emitter(target, source, env): 
    env.Depends(target, env.Value(env.subst('$MY_VAR'))) 
    return target, source 
bld = Builder(action=bld_func, emitter=bld_emitter) 

完全SConstruct：

# Create a builder that depends upon an environment variable 
def bld_func(target, source, env): 
    with open(str(target[0]), 'w') as f: 
     f.write(' '.join(str(t) for t in target) + '\n') 
     f.write(' '.join(str(s) for s in source) + '\n') 
     f.write(env.subst('$MY_VAR') + '\n') 
def bld_emitter(target, source, env): 
    env.Depends(target, env.Value(env.subst('$MY_VAR'))) 
    return target, source 
bld = Builder(action=bld_func, emitter=bld_emitter) 

# Attach it to an environment 
env = Environment() 
env['BUILDERS']['BLD'] = bld 

# Invoke the builder 
env.BLD('output.txt', 'input.txt', MY_VAR=ARGUMENTS['MY_VAR']) 

輸出示例：

$ scons -Q MY_VAR=cc output.txt 
bld_func(["output.txt"], ["input.txt"]) 
$ scons -Q MY_VAR=gcc output.txt 
bld_func(["output.txt"], ["input.txt"]) 
$ scons -Q MY_VAR=gcc output.txt 
scons: `output.txt' is up to date.